I noted in an earlier post that one of the potential conflicts of quantum mechanics and general relativity is the potential of a point-like particle with rest mass to blow up into a singularity, since there is infinite density in a point-like particle with rest mass.
But, if fundamental particles are given volume, this problem disappears. If that volume is on the order of the Planck mass or greater, the distortion of the space-time continuum resulting from any given fundamental particle is far below the limits of experimental methods to detect, and that if the fundamental particles are sphere-like and have a radius on the order of 10^-41 meters, that you reach a size where the time dialation effects of gravity fields in general relativity could conceivably explain CP violation in quantum mechanics.
There are also other quite different disconnect between general relativity and quantum mechanics.
General relativity's equations observes locality, at least in "small" areas of space-time. Quantum mechanics does not, at least in the case of entangled quanta that were once interacting in a way that synchronized their quantum states.
Further, quantum mechanics can get from point A to point B over paths that would seem impossible by any path if a classical particle with a fixed mass and momentum and original location with values for those equal something in the middle of the range that were the fundamental particle is smeared by the uncertainty principle would lie (this is called quantum tunnelling, and while it isn't strictly an instance of non-locality, it is non-intuitive for similar reasons).
Reconciling these aspects is not easy, although the quantum mechanical effects usually become virtually invisible at the scales and in the circumstances where general relativity applies to deviate from special relativity in four dimensional Minkowski space, where the equations of quantum mechanics in the Standard Model are defined.
True non-locality requires either a rethinking of the meaning of causality in the context of Feynman diagram connected particles, or a concept a bit like fate or destiny for a quantum particle.
Entanglement experiements involve the separation of space of two particles that were once in contact, the triggering of the collapse of the wave function on one of them in a way that reveals its state, and the measurement of the collapsed wave function of the other, which always corresponds correctly to its entangled twin, even though the wave functions of neither quantum was collapsed when they were together as tested by proofs of wave-like behavior between the common point of origin and the point of wave function collapse.
I may be wrong (and need to check), but my understanding is that entangled prticles don't necessary have collapsed wave functions at the same time, the second one collapsed is simply observed to have a state corresponding to the state of the first one collapsed when the second collapse eventually happens.
One way for this to happen is for a chain of causality to ride backwards in time along the particle whose wave function collapses first to the point of entanglement and then forward in time again to the entangled particle at the point when it collapses, passing continuously through space-time at no more than the speed of light, but involving causation that counterintuitively involves backward motion in time.
Another way for this to happen is for the entangled particles upon separating and while they are in a wave-like uncollapsed state to have an already defined but unexpressed collapse state that they are destined to take whenever a collapse happens in either case, if this "collapse destiny property" is set at the moment of entanglement, even though it isn't expressed until much later. Indeed, perhaps every quantum particle has a destined collapse state at the moment it comes into being as an uncollapsed quantum entity, that expresses when that collapse actually takes place. This destiny would be fundamentally and theoretically impossible for an observer to determine, not just experimentally impossible to determine, until the wave function of at least one of the entangled particles collapsed.
Note that this "destiny" concept is not deterministic in the overall sense. A particles collapse state is deterministic as of the time of collapse, but an exactly equivalent randomness to the conventional description takes place at the time that the particle becomes wave-like and uncollapsed. Quantum mechanics is just as random as it is under the conventional explanation, but the dice are rolled sooner and each quanta makes its way to the point of its ultimate wave function collapse with an invisible property that describes what will happen at that point - thus a uncollapsed wave function state of a quantum particle contains more information than is conventionally attributed to it. It carries a secret set of instructions about what to do when it arrives at its destination with it that is never revealed unless a co-conspirator rats out this information to the observer.
Similarly, maybe while every W boson acts exactly the same, a W boson's decay products are randomly determined when it is born, rather than when it decays. But, this does pose a problem, because the decay products of a W boson or an energetic photon that spontaneously gives rise to a particle and its antiparticle, must observe mass energy conservation, and the energy of a boson can change before it decays into something else or is absorbed. Hence, a quanta's destiny, if there is one, can be fixed no earlier than at the last time that it interacts with another quanta, rather than at its birth, and if this is the destiny rule, then the existence or non-existence of gravitons matters a great deal, as gravity could in theory change a particle's destiny by imparting momentum to it that make it possible to decay to a higher energy set of products and thus change the options in its desinty. Otherwise, gravitationally induced momentum shouldn't play a part in matter-energy conservation in decay products, yet surely, momentum of one kind shouldn't act differently than momentum of another under the equivalence principle.
Since this hidden destiny property of quanta doesn't manifest physically at all during the uncollapsed wave-like state of a quanta, it also shouldn't impact quantum mechanical phenomena like quantum tunnelling which are necessary to make such common devices as transistors work.
As long as this exact information doesn't have any impact on how the wave function propogates, this secret destiny idea could resolve epistomological and mathematical issues with non-locality without actually changing anything about how quanta behave in the physical world and might help improve our intuition about how to describe precisely what it is that triggers wave function collapse. This interpretation would also circumvent the ugliness of the many worlds interpretation of quantum mechanics, while not resorting to the full fledged pilot waves of Bohmian interpretations.
I'm sure that there are many ways that what I am saying could be wrong or ruled about empirically in quantum mechanics, but if that is the case then there must be some detail of it that I am misformed about and misunderstand, which as I am a layman, coulud certainly be the case. Also, like other "interpretations" of quantum mechanics this doesn't in and of itself change anything about what the equations predict in the real world.
But, this interpretation, if it works, might make it easier to mathematically formulate an integration of quantum mechanics and general relativity that does not require true non-locality, or true backwards in time causality.
It is also worth noting that while the working excellently fit to the data theory of quantum mechanics is that it is truly stochastic, that if the seemingly random results were actually the function of a highly sensitive to initial conditions chaotic function (e.g. the nth root of the moduli of location in a Klein-Kaluza suppressed dimension of space-time of a scale much less than 10^-41 meters at the place where "the dice are rolled") that it could appear perfectly random while actually being deterministic. Since the experimental results that we are currently capable of generating aren't any different under either scenario, this isn't very interesting. But, if some other aspect of the theory suggested a topology of space-time that would motivate this kind of deterministic function, it might become attractive as a means of unifying equations into some deeper theory.
Friday, August 12, 2011
Wednesday, August 10, 2011
Issues Worth Examining
Usually I discuss new findings in science. Today, I'll identify a number of issues that science has, nearly has, and may have the tools to answer, but have not yet been resolved.
1. Is there any archaeological evidence of Sumerian or Egyptian cultural influence to the north of the Aegean and Anatolia and the Mediterranean Coast?
We know that the area north of the Aegean and Anatolia, particularly the Balkans, was a stopping off point for the further Neolithic settlement of Europe by farmers and herders the earliest of which is the Linear Pottery Culture (LBK). There is a "fan" of population genetic influence (e.g. Y-DNA haplogroup E) that appears to be North African in origin that extends well into the Balkans. There are multiple eras when this could have arrived: early Neolithic, during the Greek silver and golden ages, during the Roman era, during the Byzantine era, as part of Slavic expansion, or under the Ottoman Empire. But, population movements in the region after the LBK and prior to any potential Greek influence are obscure.
The Egyptian and Sumerian empires are not known to have ever extended beyond Southern Anatolia and perhaps a few fringe Aegean islands in recorded history.
There are some suggestive cave paintings in the Caspian Sea that would seem to show Egyptian style boats at a time when the Egyptians would have had that kind of boat. There is some evidence of fairly sophisticated canal system connecting the Black and Caspian Seas at some point in history. There have also been some suggestions of a Sumerian linguistic influence on some or all Uralic languages.
As one of the earliest loci of Indo-European language speakers, these traces would have to be quite early. Also, Egyptian record keeping and Sumerian records, to my knowledge, do not document these kinds of expeditions, but these records were hardly comprehensive, particularly in the earlier eras.
Finding such a link, or definitively ruling it out, would be helpful either way in piecing together chains of causation in prehistory.
2. The sporadic v. familial model in evaluating the etiology of IQ.
Considerable research has been devoted to the causes of mental retardation, particularly where it arises without a family history of it, and considerable research has been devoted to establishing that IQ, in general, has a strong hereditary component that can be discerned from familial similarities in IQ at different degrees of relatedness.
One area that probably deserves more research is to examine "sporadic" instances of high IQ. In other words, what can we learn about the nature of IQ from looking genetically and from a nurture perspective at very high IQ people with much lower IQ parents. Are these mostly cases of parents who had good genes that were suppressed by bad environments that were not shared by the child? Are these cases of new mutations in the child that were not present in the parent? Are these cases of recessive genes that did not express in either parent? Are these casees of exceptionally good parenting choices? Are these cases of inaccurately assigned paternity? Or what?
3. Where does South Asian Y-DNA haplogroup T come from?
Areas more or less similar to the proto-Dravidian area of South Asia, and also certain tribal groups in Eastern South Asia, have high concentrations of Y-DNA haplogroup T. What kind detailed subtyping of these haplogroups tell us about where they fit in the phylogeny of Y-DNA haplogroup T and whether these Y-DNA types are autochronous or have some specific geographic origin elsewhere? What can study of these haplogroups tell us about time that this haplogroup emerged in that location?
It does not appear to have origins in Pakistan and is centered on the Eastern side of South Asia with a stark discontinuity between it and the Northwest. If it is part of either an Ancesteral North Indian or Ancestral South Indian genetic package at all, it is a part of the Ancestral South Indian genetic package that is not associated with Harappan or Indo-Aryan influence. Yet, ASI is often seen as indigeneous to the subcontinent, while Y-DNA haplogroup T has clear affinities to the European/West Asian/Northern and Eastern African region (i.e. "Western influence.") It could be that autosomal analysis is conflating Western influence via Harappan and Indo-Aryan populations and Western influence associated with Y-DNA haplogroup T associated with a separate, distinct and earlier migration, since the two Western influences may be closer genetically to each other than they ANI and ASI are to each other.
My intuition is that detailed study will show origins of the South Asian subtypes in phylogenies rooted in Southern Egypt, Sudan, Ethiopia and Somolia, and that an appropriately chosen mutation rate aging methodology will be consistent with the South Asian Neolithic and proto-Dravidian language, suggesting that migrants from South Asia were instrumental in this historical events. But, population genetics can shed much better light on the question. Detailed phylogenies of Y-DNA haplogroup T have been done, but they did not extend to South Asian samples, so study of those samples is a final step necessary to prove or disprove the hypothesis that Y-DNA haplogroup T men were instrumental in the formative period of Dravidan culture.
4. What distinguishes socioeconomically successful people who are similar in IQ, have only a high school education and have similar socioeconomic status to begin with?
A junior high school or high school teacher in a low income neighborhood has a great many students of the same socioeconomic status, and whatever environmental influences out there impact IQ have already transpired for the most part. These teachers have the hand that they have been dealt and so do their students at that point.
Lots of studies show education and IQ as pivotal for success in low socioeconomic status kids. But, what about the kids for whom earning a college degree is not a realistic option given their mediocre academic performance to date, even if they are able to stick it out and graduate from high school?
What choices and factors distinguish the winners and losers in life, in terms of socioeconomic success, once these parameters are set?
Insufficient good research looks at this issue which is a practical concern to a very large numbers of teachers, mentors, and kids. Good research on this point could provide an empirical basis to enhance middle school and high school curriculums for a group of students who often simply receive a watered down version of a college preparatory curriculum directed towards an educational trajectory that they are very unlikely to follow with success.
A great deal of effort has been devoted to researching how to improve academic performance, but despite study after study that shows that very little consistently improves academic performance in a consistent way once variables like socioeconomic class and past academic performance and IQ are controlled for, despite herculean efforts to find approaches that do, perhaps at least a little more research should be devoted not to improving the academic performance of these academically mediocre kids, but to accept for a moment that some kids, indeed a great many kids, are going to be academically mediocre, and to figure out in a way that accepts this as a given, what their best options in life are and what choices are most important to their lifetime prosperity.
Also, to the extent that there are inborn personality traits that have an impact on this result (something shown in high IQ individuals already by the Termain study, for example), what can we say about optimal approaches for kids with different personalities profiles?
Perhaps some of these lessons can be replicated.
5. What distinguishes misdemeanor recidivists?
Felony recidivism is heavily studied.
Misdemeanor recidivision (and misdemeanor sentencing in general) is not. We need more basic information about who misdemeanor recividists are, how differential treatment of them in the criminal justice system can impact crime rates and criminal justice system resources, how authorized sentences differ from imposed sentences by offense type, offender type, and aggravating circumstances, and how discretion in the criminal justice system is exercised both in bond matters and plea bargaining and sentencing in misdemeanor criminal matters.
1. Is there any archaeological evidence of Sumerian or Egyptian cultural influence to the north of the Aegean and Anatolia and the Mediterranean Coast?
We know that the area north of the Aegean and Anatolia, particularly the Balkans, was a stopping off point for the further Neolithic settlement of Europe by farmers and herders the earliest of which is the Linear Pottery Culture (LBK). There is a "fan" of population genetic influence (e.g. Y-DNA haplogroup E) that appears to be North African in origin that extends well into the Balkans. There are multiple eras when this could have arrived: early Neolithic, during the Greek silver and golden ages, during the Roman era, during the Byzantine era, as part of Slavic expansion, or under the Ottoman Empire. But, population movements in the region after the LBK and prior to any potential Greek influence are obscure.
The Egyptian and Sumerian empires are not known to have ever extended beyond Southern Anatolia and perhaps a few fringe Aegean islands in recorded history.
There are some suggestive cave paintings in the Caspian Sea that would seem to show Egyptian style boats at a time when the Egyptians would have had that kind of boat. There is some evidence of fairly sophisticated canal system connecting the Black and Caspian Seas at some point in history. There have also been some suggestions of a Sumerian linguistic influence on some or all Uralic languages.
As one of the earliest loci of Indo-European language speakers, these traces would have to be quite early. Also, Egyptian record keeping and Sumerian records, to my knowledge, do not document these kinds of expeditions, but these records were hardly comprehensive, particularly in the earlier eras.
Finding such a link, or definitively ruling it out, would be helpful either way in piecing together chains of causation in prehistory.
2. The sporadic v. familial model in evaluating the etiology of IQ.
Considerable research has been devoted to the causes of mental retardation, particularly where it arises without a family history of it, and considerable research has been devoted to establishing that IQ, in general, has a strong hereditary component that can be discerned from familial similarities in IQ at different degrees of relatedness.
One area that probably deserves more research is to examine "sporadic" instances of high IQ. In other words, what can we learn about the nature of IQ from looking genetically and from a nurture perspective at very high IQ people with much lower IQ parents. Are these mostly cases of parents who had good genes that were suppressed by bad environments that were not shared by the child? Are these cases of new mutations in the child that were not present in the parent? Are these cases of recessive genes that did not express in either parent? Are these casees of exceptionally good parenting choices? Are these cases of inaccurately assigned paternity? Or what?
3. Where does South Asian Y-DNA haplogroup T come from?
Areas more or less similar to the proto-Dravidian area of South Asia, and also certain tribal groups in Eastern South Asia, have high concentrations of Y-DNA haplogroup T. What kind detailed subtyping of these haplogroups tell us about where they fit in the phylogeny of Y-DNA haplogroup T and whether these Y-DNA types are autochronous or have some specific geographic origin elsewhere? What can study of these haplogroups tell us about time that this haplogroup emerged in that location?
It does not appear to have origins in Pakistan and is centered on the Eastern side of South Asia with a stark discontinuity between it and the Northwest. If it is part of either an Ancesteral North Indian or Ancestral South Indian genetic package at all, it is a part of the Ancestral South Indian genetic package that is not associated with Harappan or Indo-Aryan influence. Yet, ASI is often seen as indigeneous to the subcontinent, while Y-DNA haplogroup T has clear affinities to the European/West Asian/Northern and Eastern African region (i.e. "Western influence.") It could be that autosomal analysis is conflating Western influence via Harappan and Indo-Aryan populations and Western influence associated with Y-DNA haplogroup T associated with a separate, distinct and earlier migration, since the two Western influences may be closer genetically to each other than they ANI and ASI are to each other.
My intuition is that detailed study will show origins of the South Asian subtypes in phylogenies rooted in Southern Egypt, Sudan, Ethiopia and Somolia, and that an appropriately chosen mutation rate aging methodology will be consistent with the South Asian Neolithic and proto-Dravidian language, suggesting that migrants from South Asia were instrumental in this historical events. But, population genetics can shed much better light on the question. Detailed phylogenies of Y-DNA haplogroup T have been done, but they did not extend to South Asian samples, so study of those samples is a final step necessary to prove or disprove the hypothesis that Y-DNA haplogroup T men were instrumental in the formative period of Dravidan culture.
4. What distinguishes socioeconomically successful people who are similar in IQ, have only a high school education and have similar socioeconomic status to begin with?
A junior high school or high school teacher in a low income neighborhood has a great many students of the same socioeconomic status, and whatever environmental influences out there impact IQ have already transpired for the most part. These teachers have the hand that they have been dealt and so do their students at that point.
Lots of studies show education and IQ as pivotal for success in low socioeconomic status kids. But, what about the kids for whom earning a college degree is not a realistic option given their mediocre academic performance to date, even if they are able to stick it out and graduate from high school?
What choices and factors distinguish the winners and losers in life, in terms of socioeconomic success, once these parameters are set?
Insufficient good research looks at this issue which is a practical concern to a very large numbers of teachers, mentors, and kids. Good research on this point could provide an empirical basis to enhance middle school and high school curriculums for a group of students who often simply receive a watered down version of a college preparatory curriculum directed towards an educational trajectory that they are very unlikely to follow with success.
A great deal of effort has been devoted to researching how to improve academic performance, but despite study after study that shows that very little consistently improves academic performance in a consistent way once variables like socioeconomic class and past academic performance and IQ are controlled for, despite herculean efforts to find approaches that do, perhaps at least a little more research should be devoted not to improving the academic performance of these academically mediocre kids, but to accept for a moment that some kids, indeed a great many kids, are going to be academically mediocre, and to figure out in a way that accepts this as a given, what their best options in life are and what choices are most important to their lifetime prosperity.
Also, to the extent that there are inborn personality traits that have an impact on this result (something shown in high IQ individuals already by the Termain study, for example), what can we say about optimal approaches for kids with different personalities profiles?
Perhaps some of these lessons can be replicated.
5. What distinguishes misdemeanor recidivists?
Felony recidivism is heavily studied.
Misdemeanor recidivision (and misdemeanor sentencing in general) is not. We need more basic information about who misdemeanor recividists are, how differential treatment of them in the criminal justice system can impact crime rates and criminal justice system resources, how authorized sentences differ from imposed sentences by offense type, offender type, and aggravating circumstances, and how discretion in the criminal justice system is exercised both in bond matters and plea bargaining and sentencing in misdemeanor criminal matters.
Tuesday, August 9, 2011
Rare Gene Variants And Genetic Conditions
An important class of genetic conditions are caused by myriad rare genetic mutations that may emerge for the first time when the person who has it is born, or may be limited to small extended lineages or fairly small populations, rather than to all of humanity.
A small number of rare genetic mutations are produced in each new generation. Advanced parental age and environmental exposures and stresses can increase their frequency, the absence of these factors can reduce their frequency.
The most harmful of these rare genetic mutations are never passed on in the gene pool because they produce miscarriages or cognenital defects that cause someone to die before reproducing or to be infertile or both. Others appear where they are mostly harmless, for example in an inactivated gene or one triggered by environmental conditions that are absent (e.g. a gene that weakens ability to handle thin oxygen at high altitude in someone who lives on a flat Pacific island), and are passed on from generation to generation as little more than evolutionarily neutral ancestry informative markers.
Certain genes are more sensitive to disruption than others. The most sensitive genes code intricate biological processes that call upon many genes to work together to function properly which can be interrupted by defects in that biological system at a great many different points. Thus, interruptions to the same system at any of these different points is going to appear phenotypically as a similar syndrome associated with the overall complex biological system's failure to work properly due to some rare genetic variant.
Autism and schizophrenia are two of many conditions that seem to fit the profile of having overwhelmingly genetic causes that act on the same or interrelated groups of biological systems in a personn causing phenomenologically similar symptoms, but in which the specific mutations that cause the syndrome vary almost as widely as the number of extended families that have cases of it.
These genetic syndromes (as noted by my source linked above) adhere to "the “Anna Karenina principle”, based on Tolstoy’s famous opening line:
“Happy families are all alike; every unhappy family is unhappy in its own way”, people without these syndromes are are alike in the relevant genes (or least exhibit a handful of common variations in those genes); people with these syndromes all differ from this fixed standard in their own way.
These conditions can be among the most severely impairing of genetic conditions, because they rely for a substantial share of their prevalance on new mutations at each generation rather than Mendelin inheritance from parents. They don't have to be fitness enhancing to endure.
In contrast, genetic conditions whose prevalance relies on the precisely same mutation being passed on from parent to child need to either be genetic fitness neutral, or genetic fitness enhancing (at least at a long run multi-generational, extended familiy level of analysis), or the genetic fitness disadvantage nature of the mutation will cause its frequency in the population to decline unless other unrelated genetic fitness boosts cause the individual's population to expand notwithstanding its other faults.
The prevalance of these conditions is a product of mutation rates per generation and the proportion of the genome that constitutes a target area that would induce these conditions if a random mutation of some type arose there. The larger the group of genes required to code a biological function, the more vulnerable it is to this kind of condition. Given the extremely complexity of the brain relative to that of the brains of most other animals, and relative to many other parts of our bodies, it isn't too surprising that many of these rare gene variant disruptions of complex systems conditions give rise to mental health conditions.
Even if every known sufferer from autism and schizophrenia and everyone who was a potential carrier of those conditions was removed from a sufficiently control population, that control population would develop new autistic and schizophrenic individuals in the very next generation and would in not many generations after that have the same prevalance of autism and schizophrenia as the source populations if environmental factors that impact mutation rates were held constant between the source and control populations.
Spontaneous v. Familial Inheritance As A Matter of Degree
Of course, Mendelin inheritance models and sponanteous rare genetic variant models are merely ideal types. Every Mendelin inherited genetic variant started at some point as a spontaneously arising rare genetic mutation. Every rare genetic variant that is passed on to at least one child has a Mendelin inheritance element.
Rare genetic variants that are dominant in expression get noticed and classified by the conditions they give rise to, and have negative fitness effects, are going to have predominantly sporadic rather than familial prevalance patterns even though they are genetic.
Recessive rare genetic variants considered
Rare genetic variants that are recessive in expression are invisible until (1) inbreeding causes someone to have two copies of the recessive gene, probably many generations later, (2) someone who has already inherited a recessive gene from a parent spontaneously has a germline mutation in the same gene from another parent (either the same, or a functionally equivalent version), or (3) two independent lineages each have mutations in the same gene (possibly many generations apart from each other) in a manner that are recessive in effect and admixture of those lineages gives rise to an individual who expresses the recessive gene variant's effect.
Given the fairly modest number of mutations per generation (IIRC about 2500) out of 3 billion genetic bases in an individual's genome, method (1), or method (3) with different versions of the recessive mutation that have the same effect, are likely to be much more common than the alternatives and from the point of view of an individual born with a recessive genetic condition it is almost always going to look like a predominantly Mendelin inheritance based genetic condition.
The odds of one novel germ line mutation from a father and one novel germline mutation from a mother of the same recessive mutation in the same gene arising at the same time in the same individual is almost nil unless it is the product of intentional manipulation or a highly targeted environmental effect (e.g. lateral gene transfer as a result of a shared germ line retroviral infection, or an environmental effect that only impacts the very end point of a chromosome for chemical geometry reasons of some kind). There is some circumstantial evidence that a retrovirus carried by a seasonal germ vector like lice may account for the seasons variation in schizophrenia (and perhaps also autism) prevalence.
Also, recessive conditions, as a result, are likely to start somewhere and see their prevalance slowly grow in a particular reproductive population due to population expansion and founder effects, or due to major selective advantages associated with them, rather than having the more random, generally global prevalance one expects in syndroms caused by rare genetic variants that influence complex biological systems that have themselves reached fixation or near fixation on a species or population.
Tell Tale Symptoms Of New Mutation Rare Gene Variant Syndromes
Strongly hereditary conditions that show similar prevalance in all global populations, like schizophrenia, are more likely to be dominant genetic conditions caused to a great extent by new rare gene variant mutations in large complex biological systems, while strongly hereditary conditions that show major frequency variations between different populations are more likely to be associated with Mendelin recessive genes.
Rare gene variants that are fitness enhancing in almost all circumstances, in contrast, whether dominant additive, or recessive, such as new mutations that enhance intelligence, should have strongly familial inheritance patterns. Every time one of these arises, it should tend to stay in the genome and should tend to stall on the road to fixation only if it interfers with some other fitness enhancing gene (perhaps either gene individually changes brain chemistry in a positive way but the presence of both genes at the same time has no effect or a negative effect) or has other negative side effects (e.g. an enhancement of connective tissue development that fosters brain connectivity but also increases the risk at any given point in life of developing connective tissue cancer, a scenario that has been proposed as a hypothetical basis for the fairly rapid spread of one of the breast cancer risk genes).
A small number of rare genetic mutations are produced in each new generation. Advanced parental age and environmental exposures and stresses can increase their frequency, the absence of these factors can reduce their frequency.
The most harmful of these rare genetic mutations are never passed on in the gene pool because they produce miscarriages or cognenital defects that cause someone to die before reproducing or to be infertile or both. Others appear where they are mostly harmless, for example in an inactivated gene or one triggered by environmental conditions that are absent (e.g. a gene that weakens ability to handle thin oxygen at high altitude in someone who lives on a flat Pacific island), and are passed on from generation to generation as little more than evolutionarily neutral ancestry informative markers.
Certain genes are more sensitive to disruption than others. The most sensitive genes code intricate biological processes that call upon many genes to work together to function properly which can be interrupted by defects in that biological system at a great many different points. Thus, interruptions to the same system at any of these different points is going to appear phenotypically as a similar syndrome associated with the overall complex biological system's failure to work properly due to some rare genetic variant.
Autism and schizophrenia are two of many conditions that seem to fit the profile of having overwhelmingly genetic causes that act on the same or interrelated groups of biological systems in a personn causing phenomenologically similar symptoms, but in which the specific mutations that cause the syndrome vary almost as widely as the number of extended families that have cases of it.
These genetic syndromes (as noted by my source linked above) adhere to "the “Anna Karenina principle”, based on Tolstoy’s famous opening line:
“Happy families are all alike; every unhappy family is unhappy in its own way”, people without these syndromes are are alike in the relevant genes (or least exhibit a handful of common variations in those genes); people with these syndromes all differ from this fixed standard in their own way.
These conditions can be among the most severely impairing of genetic conditions, because they rely for a substantial share of their prevalance on new mutations at each generation rather than Mendelin inheritance from parents. They don't have to be fitness enhancing to endure.
In contrast, genetic conditions whose prevalance relies on the precisely same mutation being passed on from parent to child need to either be genetic fitness neutral, or genetic fitness enhancing (at least at a long run multi-generational, extended familiy level of analysis), or the genetic fitness disadvantage nature of the mutation will cause its frequency in the population to decline unless other unrelated genetic fitness boosts cause the individual's population to expand notwithstanding its other faults.
The prevalance of these conditions is a product of mutation rates per generation and the proportion of the genome that constitutes a target area that would induce these conditions if a random mutation of some type arose there. The larger the group of genes required to code a biological function, the more vulnerable it is to this kind of condition. Given the extremely complexity of the brain relative to that of the brains of most other animals, and relative to many other parts of our bodies, it isn't too surprising that many of these rare gene variant disruptions of complex systems conditions give rise to mental health conditions.
Even if every known sufferer from autism and schizophrenia and everyone who was a potential carrier of those conditions was removed from a sufficiently control population, that control population would develop new autistic and schizophrenic individuals in the very next generation and would in not many generations after that have the same prevalance of autism and schizophrenia as the source populations if environmental factors that impact mutation rates were held constant between the source and control populations.
Spontaneous v. Familial Inheritance As A Matter of Degree
Of course, Mendelin inheritance models and sponanteous rare genetic variant models are merely ideal types. Every Mendelin inherited genetic variant started at some point as a spontaneously arising rare genetic mutation. Every rare genetic variant that is passed on to at least one child has a Mendelin inheritance element.
Rare genetic variants that are dominant in expression get noticed and classified by the conditions they give rise to, and have negative fitness effects, are going to have predominantly sporadic rather than familial prevalance patterns even though they are genetic.
Recessive rare genetic variants considered
Rare genetic variants that are recessive in expression are invisible until (1) inbreeding causes someone to have two copies of the recessive gene, probably many generations later, (2) someone who has already inherited a recessive gene from a parent spontaneously has a germline mutation in the same gene from another parent (either the same, or a functionally equivalent version), or (3) two independent lineages each have mutations in the same gene (possibly many generations apart from each other) in a manner that are recessive in effect and admixture of those lineages gives rise to an individual who expresses the recessive gene variant's effect.
Given the fairly modest number of mutations per generation (IIRC about 2500) out of 3 billion genetic bases in an individual's genome, method (1), or method (3) with different versions of the recessive mutation that have the same effect, are likely to be much more common than the alternatives and from the point of view of an individual born with a recessive genetic condition it is almost always going to look like a predominantly Mendelin inheritance based genetic condition.
The odds of one novel germ line mutation from a father and one novel germline mutation from a mother of the same recessive mutation in the same gene arising at the same time in the same individual is almost nil unless it is the product of intentional manipulation or a highly targeted environmental effect (e.g. lateral gene transfer as a result of a shared germ line retroviral infection, or an environmental effect that only impacts the very end point of a chromosome for chemical geometry reasons of some kind). There is some circumstantial evidence that a retrovirus carried by a seasonal germ vector like lice may account for the seasons variation in schizophrenia (and perhaps also autism) prevalence.
Also, recessive conditions, as a result, are likely to start somewhere and see their prevalance slowly grow in a particular reproductive population due to population expansion and founder effects, or due to major selective advantages associated with them, rather than having the more random, generally global prevalance one expects in syndroms caused by rare genetic variants that influence complex biological systems that have themselves reached fixation or near fixation on a species or population.
Tell Tale Symptoms Of New Mutation Rare Gene Variant Syndromes
Strongly hereditary conditions that show similar prevalance in all global populations, like schizophrenia, are more likely to be dominant genetic conditions caused to a great extent by new rare gene variant mutations in large complex biological systems, while strongly hereditary conditions that show major frequency variations between different populations are more likely to be associated with Mendelin recessive genes.
Rare gene variants that are fitness enhancing in almost all circumstances, in contrast, whether dominant additive, or recessive, such as new mutations that enhance intelligence, should have strongly familial inheritance patterns. Every time one of these arises, it should tend to stay in the genome and should tend to stall on the road to fixation only if it interfers with some other fitness enhancing gene (perhaps either gene individually changes brain chemistry in a positive way but the presence of both genes at the same time has no effect or a negative effect) or has other negative side effects (e.g. an enhancement of connective tissue development that fosters brain connectivity but also increases the risk at any given point in life of developing connective tissue cancer, a scenario that has been proposed as a hypothetical basis for the fairly rapid spread of one of the breast cancer risk genes).
Schizophrenia Causation Better Understood
About 80% of schizophrenia cases are estimated to be hereditary. The other 20% of cases are sporadic, not having an apparent familial cause.
A new study suggests that at least half of sporadic cases are attributable to genetic mutations that arise for the first time in them and are not present in their parents, something that tends to have an elevated frequency in children with older fathers (the risk factor is called advanced paternal age).
Thus, at least 90% of schizophrenia cases are genetic, even though just 80% are hereditary. Evidence has also pointed to seasonal tick infections around the start of a pregnancy, low vitamin D levels during pregnancy, and rare recessive genes of inbred individuals as possible causes of sporadic schizophrenia.
This combined pattern of causes make schizophrenia makes its causes better understood than almost any other mental health condition, which is appropriate because schizophrenia is quite common, with about 2.2 million Americans affected.
A new study suggests that at least half of sporadic cases are attributable to genetic mutations that arise for the first time in them and are not present in their parents, something that tends to have an elevated frequency in children with older fathers (the risk factor is called advanced paternal age).
Thus, at least 90% of schizophrenia cases are genetic, even though just 80% are hereditary. Evidence has also pointed to seasonal tick infections around the start of a pregnancy, low vitamin D levels during pregnancy, and rare recessive genes of inbred individuals as possible causes of sporadic schizophrenia.
This combined pattern of causes make schizophrenia makes its causes better understood than almost any other mental health condition, which is appropriate because schizophrenia is quite common, with about 2.2 million Americans affected.
Lost Civilizations
No amount of searching will unearth ancient astronauts or ancient cultures with anything close to the level of technology that we enjoy today. But, there is still something stirring about the search for lost civilizations. Making sense of the Sumerians and the Minoans. Unraveling the origins of the first civilizations we can identify from the historic period in the prehistoric Neolithic cultures that came before them. Piecing together the family tree of the languages we know of in history, some themselves lost, to connect them into a larger whole. Tracing the migrations of man from Africa to points across the globe to discern how the peoples that inhabit it now came to be. Looking at history on the scale of millenia. Identifying the sources of are archaetypical myths, giving them the context from the times that they originated. Unearthing the substrates in our contemporary languages and cultures to reveal their mixed origins. Learning the details of the process by which we became farmers and herders. Determining if the cultures that died were victims of war, of changing climate, or of the collapse of their own organizing principles.
Part of it is an act of overcoming demons and ghosts and myths of the past by gaining a better understanding of where they came from in the first place, of piercing back beyond the veils of our oldest layers of myth and legend and religious doctrine. Nothing demystifies the Biblical Philistines, for example, more than being able to figure out that they were real people, being able to determine when they arrived and where and from whom, being able to understand that larger forces that drove their exile, and being able to make sense of their culture from the perspective of disinterested outsiders rather than warring Levantine factions.
Where did we come up with tales like Atlantis and Lemuria? Were Sumerian and Egyptian myths original, arising with writing, or were they much older oral traditions? How much older?
We live in an era where it seems we have a genuine capacity to answer some of those questions with new methodologies and technologies, and when the evidence has not irrevocably been erased.
Tracing our ancient history in detail also sheds light on who were are as a species on a grand scale. What are we capable of? What drives the rise and fall of empires? What causes new languages to form and old ones to die? What are the cyclical trends of deep history? What are the trends where progress seems inevitable? To the extent that we can determine definitively what happend in pre-history, can we at least model it well enough to determine the processes and forces that shaped it? What factors drove history? Which factors were merely secondary?
We know which cultures survived. We don't know nearly as well which cultures did not, or why they succumbed to that cultures of others. Can we put the myriad bits and pieces we understand about our deep past into a coherent narrative? Can we tell a Genesis story that has more than oral tradition and old books of uncertain veracity to back them up? We have the broad outlines of that story, but filling in the detail breathes life into it, makes it real.
Part of it is an act of overcoming demons and ghosts and myths of the past by gaining a better understanding of where they came from in the first place, of piercing back beyond the veils of our oldest layers of myth and legend and religious doctrine. Nothing demystifies the Biblical Philistines, for example, more than being able to figure out that they were real people, being able to determine when they arrived and where and from whom, being able to understand that larger forces that drove their exile, and being able to make sense of their culture from the perspective of disinterested outsiders rather than warring Levantine factions.
Where did we come up with tales like Atlantis and Lemuria? Were Sumerian and Egyptian myths original, arising with writing, or were they much older oral traditions? How much older?
We live in an era where it seems we have a genuine capacity to answer some of those questions with new methodologies and technologies, and when the evidence has not irrevocably been erased.
Tracing our ancient history in detail also sheds light on who were are as a species on a grand scale. What are we capable of? What drives the rise and fall of empires? What causes new languages to form and old ones to die? What are the cyclical trends of deep history? What are the trends where progress seems inevitable? To the extent that we can determine definitively what happend in pre-history, can we at least model it well enough to determine the processes and forces that shaped it? What factors drove history? Which factors were merely secondary?
We know which cultures survived. We don't know nearly as well which cultures did not, or why they succumbed to that cultures of others. Can we put the myriad bits and pieces we understand about our deep past into a coherent narrative? Can we tell a Genesis story that has more than oral tradition and old books of uncertain veracity to back them up? We have the broad outlines of that story, but filling in the detail breathes life into it, makes it real.
Monday, August 8, 2011
Comma Before Because
Language log has a post regarding the fact that you can put a comma before the word "because" in literate formal written English, notwithstanding the belief of some grammar instructors that you may not.
But, I'm wondering if the real problem isn't the inaccuracy of the rule, but a misstatement of what the putative rule really says. It is one thing to say that the word "because" does not necessarily require a comma simply because it is present in a sentence, which may be the true rule, and another to say that it can never carry a comma even if another grammatical rule calls for it, which the examples cited in the rebuttal of the rule seem to imply (for example, the commas following ordinal introductions to sentences in Alice in Wonderland).
But, I'm wondering if the real problem isn't the inaccuracy of the rule, but a misstatement of what the putative rule really says. It is one thing to say that the word "because" does not necessarily require a comma simply because it is present in a sentence, which may be the true rule, and another to say that it can never carry a comma even if another grammatical rule calls for it, which the examples cited in the rebuttal of the rule seem to imply (for example, the commas following ordinal introductions to sentences in Alice in Wonderland).
The Weak Force and Mass Musings
Known Facts
* There is only one force that interacts only with particles with rest mass (all fermions and W bosons and Z bosons) and does not interact with particles without rest mass (photons and gluons). It is the weak force. Of course, one could argue that it only interacts with left handed and not right handed versions of those particles. But, still, there is not entire class of particles which does not have weak force interactions.
The weak force is also the only fundamental force that changes the rest mass of a particle thought its interactions.
The weak force causes particles with greater rest mass to decay into particles with lower rest mass more often than it gives rise to particles with greater rest mass from lower rest mass (of course, in all cases subject to total mass-energy conservation). And, in general, the greater a particle's rest mass, the more rapidly is decays.
The mass of the W and Z bosons was accurately predicted from theory using a unified electroweak theory and empirically proven physical constants that do not involve the strong force or gravity.
* The strong force does not interact with leptons, W bosons and Z bosons which have rest mass. It does interact with gluons which lack rest mass.
The strong force appears to play a significant role in the mass of composite particles that have color force charge, as illustrated, for example, by models of the mass of glueball in low energy QCD. I don't understand QCD well enough to know if the role of the strong force in establishing mass of strong force interacting particles is entirely a product of binding energy or has some additional component as well. For example, about 90% of the mass in the nucleons is due to the strong interaction between quarks and gluons, and the mass of the quarks and/or EM interaction between the quarks contribute the remaining [mass] according to QCD calculations of proton mass from first principles. (Spelled out in greater detail here and here.) Indeed, since the vast majority of the mass in the universe that is neither dark matter nor dark energy comes from protons and neutrons, and 90% of the mass in protons and neutrons comes from strong interactions, strong interactions account for the vast amount of ordinary matter rest mass in the universe.
Quarks, which have color charge, are much heavier than leptons, although the W and Z bosons are quite heavy in the absence of color charge.
* It is true that both of the particles that lack rest mass (the photon and gluon) also lack electromagnetic charge. But, the converse is not true. Neither the massive neutrinos nor the Z boson have an electromagnetic charge, but each of them do have a rest mass.
The electromagentic charge neutral baryon called the neutron, and the electromagnetic charge neutral Z boson, are both heavier than their charged counterparts the proton and the W boson.
Also, while the photon does not have an electromagnetic charge of its own, it does participate in electromagnetic interactions as its carrier boson, despite its lack of rest mass.
* Gravity influences the course taken by photons that have no rest mass as well as particles that do have rest mass. Conversely, energy as well as rest mass can induce gravity in the stress-energy tensor.
More speculative points linking the weak force and mass
* The Standard Model Higgs is really a Higgs triplet. But, two of the members of the Higgs triplet are "eaten" by the W and Z bosons which are the carrier bosons of the weak force. Given the central role that the hypothetical Higgs boson plays in the creation of inertia mass, this is an interesting fact.
* The Higgs boson, which is presumed to be quite massive, is also presumed to experience weak force decay that can be observed. It is also presumed to lack spin and electromagnetic charge and color charge.
* Composite particles in which a significant share of the particle's rest mass is attributable to binding energy appear to behave no differently in terms of inertial or gravitational mass than fundamental particles of the same mass.
This is suggestive of the idea of rest mass as a quantity that could be the product of multiple kinds of interactions.
It is also suggestive of the idea that mass could be generated mostly, or entirely, by the binding interactions between massless or extremely light preons, or alternatively, from weak force interactions between fundamental particles.
* There is considerable intuition among particle physics researchers that there is some deep relationship between the masses of the fermions and the entries in the CKM and PMNS matrixes. It seems likely that a single underlying principle, if there is one, explains both of these sets of constants in the Standard Model from some more fundamental theory. The relationship seems to be one in some way linked through the square root of rest mass rather than rest mass itself. We normally think about mass as driving transition matrixes, but we could also imagine transition matrixes driving masses. Indeed, if the two are bound up in some master equation, asking which one drives which may be a nonsense question.
* Z boson interactions do not themselves appear to produce changes in the rest mass of the particles that emit or absorb Z bosons, although Z boson decay does involve products that differ in rest mass from the rest mass of the Z boson.
* One of the predominant weak force interactions in nature is beta decay (the other is neutrino oscillation). In its most typical form it involves a bottom quark emitting a W- boson and becoming an up quark. The W- boson in the typical case (and sometimes the only case permitted by mass-energy conservation) then typically, in turn, decays into an electron and anti-neutrino of the electron neutrino type. The rest mass of the bottom quark is not precisely the same as the rest mass of the up quark plus the rest mass of the electron plus the rest mass of the electron anti-neutrino, but the mass gap between the source and the products in beta decay is very slight.
The rest mass gap in weak force interactions higher generation particles of the same types of fermions is much greater.
* Rest mass is not the only factor at work in the rate of weak force decay of composite particles. Their decay rates are also related to spin (with higher spin particles decaying more rapidly) and perhaps to electromagnetic charge also (with higher charge particles decaying more rapidly).
* CP violations in the weak force are associated with high rest mass fundamental particles that participate in the weak force interaction.
* While we think of the weak force as being weaker than the strong force, weak force driven top quark decay involving the highest mass fundamental particle happens before the strong force has an opportunity to hadronize the top quark, even though the weak force boson is massive and hence slower than the massless gluon which presumably moves at the speed of light.
* All particles with rest mass except up and down quarks in protons and neutrons that are bound into atomic nuclei, and electrons, are unstable. Even electron neutrinos and electron anti-neutrinos oscillate rather than maintaining a stable ground state.
* The theorized graviton, would have spin-2, no rest mass, no electrical charge and no color charge. If the rest mass/weak force hypothesis holds true, this boson would not have weak force interactions either.
* All quarks and charged leptons are believed to have "Dirac mass" related to Higgs field interactions, while there is some speculation that neutrinos might derive their mass from anthor source called "Majorana mass" or from a combination of the two kinds of mass. See, e.g. here. The non-detection of neutrinoless double beta decay to date, however, subject to increasingly stringent experimental limits, casts doubt on the existence of Majorana mass as a physical proces.
* We infer neutrino mass from its weak force oscillations, not necessarily from its direct detection.
* There is only one force that interacts only with particles with rest mass (all fermions and W bosons and Z bosons) and does not interact with particles without rest mass (photons and gluons). It is the weak force. Of course, one could argue that it only interacts with left handed and not right handed versions of those particles. But, still, there is not entire class of particles which does not have weak force interactions.
The weak force is also the only fundamental force that changes the rest mass of a particle thought its interactions.
The weak force causes particles with greater rest mass to decay into particles with lower rest mass more often than it gives rise to particles with greater rest mass from lower rest mass (of course, in all cases subject to total mass-energy conservation). And, in general, the greater a particle's rest mass, the more rapidly is decays.
The mass of the W and Z bosons was accurately predicted from theory using a unified electroweak theory and empirically proven physical constants that do not involve the strong force or gravity.
* The strong force does not interact with leptons, W bosons and Z bosons which have rest mass. It does interact with gluons which lack rest mass.
The strong force appears to play a significant role in the mass of composite particles that have color force charge, as illustrated, for example, by models of the mass of glueball in low energy QCD. I don't understand QCD well enough to know if the role of the strong force in establishing mass of strong force interacting particles is entirely a product of binding energy or has some additional component as well. For example, about 90% of the mass in the nucleons is due to the strong interaction between quarks and gluons, and the mass of the quarks and/or EM interaction between the quarks contribute the remaining [mass] according to QCD calculations of proton mass from first principles. (Spelled out in greater detail here and here.) Indeed, since the vast majority of the mass in the universe that is neither dark matter nor dark energy comes from protons and neutrons, and 90% of the mass in protons and neutrons comes from strong interactions, strong interactions account for the vast amount of ordinary matter rest mass in the universe.
Quarks, which have color charge, are much heavier than leptons, although the W and Z bosons are quite heavy in the absence of color charge.
* It is true that both of the particles that lack rest mass (the photon and gluon) also lack electromagnetic charge. But, the converse is not true. Neither the massive neutrinos nor the Z boson have an electromagnetic charge, but each of them do have a rest mass.
The electromagentic charge neutral baryon called the neutron, and the electromagnetic charge neutral Z boson, are both heavier than their charged counterparts the proton and the W boson.
Also, while the photon does not have an electromagnetic charge of its own, it does participate in electromagnetic interactions as its carrier boson, despite its lack of rest mass.
* Gravity influences the course taken by photons that have no rest mass as well as particles that do have rest mass. Conversely, energy as well as rest mass can induce gravity in the stress-energy tensor.
More speculative points linking the weak force and mass
* The Standard Model Higgs is really a Higgs triplet. But, two of the members of the Higgs triplet are "eaten" by the W and Z bosons which are the carrier bosons of the weak force. Given the central role that the hypothetical Higgs boson plays in the creation of inertia mass, this is an interesting fact.
* The Higgs boson, which is presumed to be quite massive, is also presumed to experience weak force decay that can be observed. It is also presumed to lack spin and electromagnetic charge and color charge.
* Composite particles in which a significant share of the particle's rest mass is attributable to binding energy appear to behave no differently in terms of inertial or gravitational mass than fundamental particles of the same mass.
This is suggestive of the idea of rest mass as a quantity that could be the product of multiple kinds of interactions.
It is also suggestive of the idea that mass could be generated mostly, or entirely, by the binding interactions between massless or extremely light preons, or alternatively, from weak force interactions between fundamental particles.
* There is considerable intuition among particle physics researchers that there is some deep relationship between the masses of the fermions and the entries in the CKM and PMNS matrixes. It seems likely that a single underlying principle, if there is one, explains both of these sets of constants in the Standard Model from some more fundamental theory. The relationship seems to be one in some way linked through the square root of rest mass rather than rest mass itself. We normally think about mass as driving transition matrixes, but we could also imagine transition matrixes driving masses. Indeed, if the two are bound up in some master equation, asking which one drives which may be a nonsense question.
* Z boson interactions do not themselves appear to produce changes in the rest mass of the particles that emit or absorb Z bosons, although Z boson decay does involve products that differ in rest mass from the rest mass of the Z boson.
* One of the predominant weak force interactions in nature is beta decay (the other is neutrino oscillation). In its most typical form it involves a bottom quark emitting a W- boson and becoming an up quark. The W- boson in the typical case (and sometimes the only case permitted by mass-energy conservation) then typically, in turn, decays into an electron and anti-neutrino of the electron neutrino type. The rest mass of the bottom quark is not precisely the same as the rest mass of the up quark plus the rest mass of the electron plus the rest mass of the electron anti-neutrino, but the mass gap between the source and the products in beta decay is very slight.
The rest mass gap in weak force interactions higher generation particles of the same types of fermions is much greater.
* Rest mass is not the only factor at work in the rate of weak force decay of composite particles. Their decay rates are also related to spin (with higher spin particles decaying more rapidly) and perhaps to electromagnetic charge also (with higher charge particles decaying more rapidly).
* CP violations in the weak force are associated with high rest mass fundamental particles that participate in the weak force interaction.
* While we think of the weak force as being weaker than the strong force, weak force driven top quark decay involving the highest mass fundamental particle happens before the strong force has an opportunity to hadronize the top quark, even though the weak force boson is massive and hence slower than the massless gluon which presumably moves at the speed of light.
* All particles with rest mass except up and down quarks in protons and neutrons that are bound into atomic nuclei, and electrons, are unstable. Even electron neutrinos and electron anti-neutrinos oscillate rather than maintaining a stable ground state.
* The theorized graviton, would have spin-2, no rest mass, no electrical charge and no color charge. If the rest mass/weak force hypothesis holds true, this boson would not have weak force interactions either.
* All quarks and charged leptons are believed to have "Dirac mass" related to Higgs field interactions, while there is some speculation that neutrinos might derive their mass from anthor source called "Majorana mass" or from a combination of the two kinds of mass. See, e.g. here. The non-detection of neutrinoless double beta decay to date, however, subject to increasingly stringent experimental limits, casts doubt on the existence of Majorana mass as a physical proces.
* We infer neutrino mass from its weak force oscillations, not necessarily from its direct detection.
Thursday, August 4, 2011
A Conjucture Regarding CP Violation And Quantum Gravity
The most clear experimental deviations from the old school three generational Standard Model are (1) neutrinos have mass, (2) we are close to ruling out a Standard Model Higgs boson, and (3) there are excessive CP violations in certain weak force interactions (i.e. this interactions do not proceed at equivalent rates forward and backward). No other Standard Model deviations are quite so definitive. Indications of a fourth generation heavy neutrino are tentative. Muon anomalous magnetic moment measurements are clouded by great uncertainty in numerical estimates of the QCD determination of one component of that calculation. Apparent CPT violations in top-antitop pairs are probably a fluke.
The Problem: Experimentally Measured CP Violations In A Nutshell
The CP violations that have been observed fit a very narrow profile. They don't happen in forces mediated by photons or gluons (the subject of a previous speculation at my other blog before this one was established), or in gravity. So far as I can tell, they have never been observed in Z boson decay of the weak force either. They have only been observed in decay chains that involve mesons with bottom or strange quarks in them decaying through W+ or W- bosons of the weak force. Top quarks almost always decay to bottom quarks, and bottom quark meson decays have been observed to show CP violation. There are probably both bottom quark and strange quark contributions to decays of mesons with bottom quarks and strange quarks in them. Charm quarks often decay to strange quarks, and neutral kaon mesons, which have strange quarks in them as part of a linear combination of two other meson types, in turn show CP violation in their decays.
It is a relatively easy thing to insert a complex numbered CP violating parameter into the CKM matrix of the Standard Model, in which the square of the matrix entries govern weak force charged flavor changing current probabilities, to capture the CP violations in neutral kaon meson decay. The current version of the Standard Model does that, but the predicted CP violation from that parameter is not big enough to account for CP violations from mesons that include bottom quarks decaying through charged weak force currents.
This is harder to fix, because if the probabilities in the CKM matrix are to add up to 100%, there are only so many degrees of freedom in the matrix and there are no parameters left to account for the excess CP violations in bottom quarks. Hence, the attractiveness of any kind of beyond the standard model theory, even one that adds a simple fourth generation of particles, thereby turning the CKM matrix into a four by four instead of a three by three matrix, that provides an additional degree of freedom or two to fit the excess CP violation seen in the decays of mesons including bottom quarks that decay via charged weak force currents.
SUSY and Technicolor theories provide other ways to add degrees of freedom but have their own problems.
A Quantum Mechanics and General Relativity Paradox
Experimental evidence to date (which recently tightened the limits on quarks not being point-like by a factor of three to four this year or last, although the limits are still far above the Planck scale of ca. 10^-35 meters proposed by many theorists to be their true size), have not found any evidence that Standard Model fundamental particles are not point-like, and have found no direct evidence of any internal structure in Standard Model fundamental particles. The ability of W boson decays to turn into almost any left handed parity fundamental particle is also a poor fit to a composite model of these particles. But, a point-like particle model poses all sorts of mathematical problems.
Classical general relativity in non-discrete space-time is not consistent with any model for the other three fundamental forces that assumes that point-like particles have mass or energy. Taken to its logical extreme (as cosmologists are a bit more comfortable doing than I am comfortable with), any amount of mass or energy in a mere point has infinite density that would give rise to a black hole singularity with an event horizon larger than the point, and would not allow bosons of any kind to escape it causing the strong force, weak force and electromagnetism to cease to function.
There is a bit of paradox here, however, in how you do the math. If you look at gravity alone, you end up with a singularity. However, if you look at the scales where the strong force, weak force and electromagnetic are observed (the first two operate at short range over a very narrow distance scale, the latter is a long range force proportionate to distance squared in the classical limit just like Newtonian gravity), with the coupling constants of each of those respective forces relative to their masses, and look at the ratio of those forces to gravity, gravity is vanishingly small and disappears from the equation.
Point-like particles moving randomly would also have a vanishingly small probability of every bumping into a force carrying boson in a geometric heuristic of quantum field theory Feynman diagram interactions which is contrary to reality.
The strong force falls off to zero at very short distances and grows to infinity at long distances, in almost the opposite of the long range electromagnetic force and gravity. The weak force is so weird it barely qualifies as a force in the conventional sense of the word - it has so much particle nature switching going on in addition to doing work pushing or pulling anything.
Of course, while quantum field theorists often talk about fundamental particles as being point-like for sake of convenience, quantum mechanics itself, with its famous uncertainty principle that makes it fundamentally and not just practically impossible to know a particle's momentum and location at the same time, in addition to contradicting Newtonian clockwork universe deterministic mechanics, also implies that even fundamental particles are in some profound way smeared at different densities over a volume of space-time (an infinite one in the extreme low density limit) rather than being truly point-like.
Quantum gravity theories overcome the singularity problem in one of two ways. Either they assume that at some scale space-time is discrete (and not necessarily perfectly local) rather than continuous and local (i.e. points in space-time can't be described with a real number coordinate system in any of its frames of reference) that reduces to general relativity in the classical scale limit, or at the quantum level, gravity is simply one more non-Abelian gauge field mediated by boson called a spin-2 graviton that is exchanged in a manner quite similar to the gluons of the strong force that interacts with mass rather than color charge and reduces to general relativity in the classical scale limit.
String theory assumes that while there are just one or two fundamental particles that manifest in all of the other fundamental particles (strings, open or closed) that those fundamental particles are not points, but instead have at least length and possibly area, in addition to retaining the uncertainty principle concept of ordinary quantum mechanics that smears fundamental particles at varying densities over a space-time region, so it has three different fixes to the gravitational singularity addressing this issue simultaneously.
Approximations And The Conjecture
Still, assume that at even very short distances that gravity behaves semi-classically in a manner analytically similar to general relativity, and that while they are fundamental that particles are sufficiently not point-like to prevent them from creating black hole singularities. The Standard Model and anything resembling it still creates lumps of very high matter-energy density interrupted by big gaps of very low matter-energy density in every case, rather than the much more homogeneous matter-energy distributions assumed for mathematical convenience in astronomy applications of general relativity. (Special relativity is built into quantum mechanics already.)
Also, assume that we are thinking about general relativity effects from a reference frame of an observer inside the fundamental particle who has the same angular momentum and linear momentum as the particle.
What does general relativity say in general about the effects of high mass-energy distributions in systems where all of the matter is at rest relative to the observer?
It says that time passes more slowly in a gravity field to the extent of that gravity field's strength according to a well defined formula. Per Wikipedia:
Now, one thing that the flavor changing charged weak force currents of meson decay in mesons involving heavy quarks where CP violations is observed have in common is that the rest mass of the particles on one side of the interaction is much greater than the rest mass of the particles on other other side of the interaction.
Thus, for our observer who follows a path along a Feynman diagram from the source heavy quark to any one of the particles the result from its decay, time is going to pass more slowly before our observer starts riding a W boson than our observer does at the other end of that W boson interaction.
So, if weak interactions proceed at the same speed from the perspective of an observer in the particle or any of the particles it couples to at either end of the interaction, from the perspective of an outside observer time will be passing more slowly at the heavy end than at the light end giving rise to different interaction speeds in different directions of the interaction.
Intuitively, it makes sense that orders of magnitude heavier mass densities are going to lead to genuine CP violations and that the heavier the heaviest particle involved in the interaction, the more pronounced the CP violation will be.
It also suggests that we ought to be able to fit that model and the known rest masses of the particles involved in the decay chains of CP violating flavor changing weak force currents to the rest mass data and the time dialation effects implied for symmetric stationary masses in general relativity to infer the mass densities at each end of the interaction, or at least the curve of possible mass density differences at each end of the interaction and infer from that a semi-classical fundamental particle radius for the particles that participate in CP violating weak force interactions, addressing these in a manner mechanically quite different than the usual arbitrary empirically determined CKM matrix component approach. These semi-classical particle radii will necessarily change less markedly than mass between the particles in this model and it may very well be possible to assign a single radius to all Standard Model fermions (and even all massive Standard Model particles including the W and Z), at least as a first order approximation, by choosing points on the mass difference-radius size cover for the interactions that show CP violations that intersect. One could also try arbitrarily using the Planck length of 1.616*10^-35 meters.
Or, one could use the Compton wavelength of the particle (which is Planck's constant divided by the speed of light divided by the particle's rest mass) (for example, about 2.5 times 10^-12 meters for an electron) to see if those would fit the data. The Compton wavelength already sets the approximate effective range of a Standard Model force and its cross-section of interaction, and dovetails with the non-CP violating nature of the electromagnetic force, which makes it particularly attractive to consider as a possible radius size (perhaps adjusted by a fixed constant as is done in the case of the Bohr radius of an electron and its classical electron radius). Using Compton wavelength, which varies porportionate to 1/mass should still cause density to increase markedly with higher generation particles whose masses increase dramatically with each higher generation of a type of fermion (although I haven't done the back of napkin calculations to confirm that yet, and would have to dig up the time dialation formula - still, the calculation of that part would be elementary - it is fitting the different time rates into the weak interaction calculations that would be a bit more subtle, although probably not beyond even my abilities with a few weeks to work on it). This would further reify the heuristic intuition associated with using a Compton wavelength to determine the cross-section of interaction of a particle in the Standard Model (on the notion that this quantified the probability that it will bump into a boson in the same space near its path).
Putting Compton wavelength into the equation for r, once gets t0=tf(1-2GM^2/hc)^-2. Simplified, that is: t0=tf(1-KM^2)^-2, for K=2G/hc. I'll have to save putting particle masses appropriately converted from electron volt units, etc. (to four significant digits 1 MeV/c^2=5.914 x 10^-7 kilograms; c=2.998*10^8 meters/second; h=6.626*10^-34 kilograms*meters^2/second; the reduced Plancks constant which is h divided by 2pi, which is natural for some quantum mechanics applications, is 1.055*10^-34 kilograms*meters^2/second, and G=6.734*10^-11 meters^3/(kilogram*seconds^2); and K with ordinary non-reduced Planck's constant is 2.131*10^-24 for masses in MeV/c^2) into this equation and comparing them to observed forward v. backward rate ratios in the flavor changing weak force currents that show CP violations for a future post, or an update to this post.
For example, using Compton's wavelength, time dialation for a bottom quark which is 4200 MeV/c^2 would be about (1-3.759*10^-17)^-2=a reduction on the order of 10^-9 (almost nil). This is more like 5700 MeV/c^2 for some of the decaying B mesons that have been shown to exhibit strong CP violation.
Using Planck's length, time dialation for a bottom quark would be determined for r=1.616*10^-35 and r0=3.722*10^-30, for a total (1-4.341*10^-6)^-2=2*10^-6.
Clearly, the length would have to be much smaller to make that kind of difference. A fundamental particle scale on the order of 10^-41 meters would be necessary to get gravitational GR effects at the levels needed to fit the CP violations we observe. But, since we already have some thin evidence that space is continuous at the sub-Planck length scale, that isn't necessarily a death blow to this idea.
Benefits Of This Approach
This would give us the first directly experimentally motivated estimate of the length scale of fundamental particles or discrete distance scales, which surely shouldn't be truly point-like in a sensible theory, as opposed to merely theoretically motivated dimensional analysis used to calculate a Planck length.
This approach would also eliminate the need to add any new particles or forces or dimensions to the Standard Model to explain the observed CP violation, although it might add a new Standard Model constant to each massive particle in the Standard Model to determine its semi-classical radius if the Compton wavelength or Planck length or some other single length for all fundamental particles in the Standard Model with rest mass doesn't provide the correct time dialation effect to fit the observed CP violations.
It would also point the way towards a more general semi-classical approach to integrating general relativity and quantum mechanics at tiny length scales which is consistent with the observation made this year that by one measure at least, space-time appears to be continuous rather than discrete at a scale well below the Planck scale. String theorists could call it the characteristic string scale, and loop quantum gravity theorists could shrug and bear it. In other words, perhaps general relativity is already perfect at arbitrarily small scales and we simply need to fix a detail about particle size in quantum mechanics.
This approach would almost necessarily work to fit the data (it has a deterministic rule to fit constants with potentially many degrees of freedom, if necessary, in fundamental particle semi-classical radii), and if it found that the Compton wavelength of a single radius worked, would add no more than one constant to the Standard Model while removing the constants associated with the CP violating parameters of the CKM matrix, producing a net wash or reduction in the number of arbitary parameters of the Standard Model with better theoretical motivation.
Of course, if the radii are all over the place for different particles, or there is not consistency between different CP violations for the some particles for some reason, this approach might not deserve to be adopted.
The Problem: Experimentally Measured CP Violations In A Nutshell
The CP violations that have been observed fit a very narrow profile. They don't happen in forces mediated by photons or gluons (the subject of a previous speculation at my other blog before this one was established), or in gravity. So far as I can tell, they have never been observed in Z boson decay of the weak force either. They have only been observed in decay chains that involve mesons with bottom or strange quarks in them decaying through W+ or W- bosons of the weak force. Top quarks almost always decay to bottom quarks, and bottom quark meson decays have been observed to show CP violation. There are probably both bottom quark and strange quark contributions to decays of mesons with bottom quarks and strange quarks in them. Charm quarks often decay to strange quarks, and neutral kaon mesons, which have strange quarks in them as part of a linear combination of two other meson types, in turn show CP violation in their decays.
It is a relatively easy thing to insert a complex numbered CP violating parameter into the CKM matrix of the Standard Model, in which the square of the matrix entries govern weak force charged flavor changing current probabilities, to capture the CP violations in neutral kaon meson decay. The current version of the Standard Model does that, but the predicted CP violation from that parameter is not big enough to account for CP violations from mesons that include bottom quarks decaying through charged weak force currents.
This is harder to fix, because if the probabilities in the CKM matrix are to add up to 100%, there are only so many degrees of freedom in the matrix and there are no parameters left to account for the excess CP violations in bottom quarks. Hence, the attractiveness of any kind of beyond the standard model theory, even one that adds a simple fourth generation of particles, thereby turning the CKM matrix into a four by four instead of a three by three matrix, that provides an additional degree of freedom or two to fit the excess CP violation seen in the decays of mesons including bottom quarks that decay via charged weak force currents.
SUSY and Technicolor theories provide other ways to add degrees of freedom but have their own problems.
A Quantum Mechanics and General Relativity Paradox
Experimental evidence to date (which recently tightened the limits on quarks not being point-like by a factor of three to four this year or last, although the limits are still far above the Planck scale of ca. 10^-35 meters proposed by many theorists to be their true size), have not found any evidence that Standard Model fundamental particles are not point-like, and have found no direct evidence of any internal structure in Standard Model fundamental particles. The ability of W boson decays to turn into almost any left handed parity fundamental particle is also a poor fit to a composite model of these particles. But, a point-like particle model poses all sorts of mathematical problems.
Classical general relativity in non-discrete space-time is not consistent with any model for the other three fundamental forces that assumes that point-like particles have mass or energy. Taken to its logical extreme (as cosmologists are a bit more comfortable doing than I am comfortable with), any amount of mass or energy in a mere point has infinite density that would give rise to a black hole singularity with an event horizon larger than the point, and would not allow bosons of any kind to escape it causing the strong force, weak force and electromagnetism to cease to function.
There is a bit of paradox here, however, in how you do the math. If you look at gravity alone, you end up with a singularity. However, if you look at the scales where the strong force, weak force and electromagnetic are observed (the first two operate at short range over a very narrow distance scale, the latter is a long range force proportionate to distance squared in the classical limit just like Newtonian gravity), with the coupling constants of each of those respective forces relative to their masses, and look at the ratio of those forces to gravity, gravity is vanishingly small and disappears from the equation.
Point-like particles moving randomly would also have a vanishingly small probability of every bumping into a force carrying boson in a geometric heuristic of quantum field theory Feynman diagram interactions which is contrary to reality.
The strong force falls off to zero at very short distances and grows to infinity at long distances, in almost the opposite of the long range electromagnetic force and gravity. The weak force is so weird it barely qualifies as a force in the conventional sense of the word - it has so much particle nature switching going on in addition to doing work pushing or pulling anything.
Of course, while quantum field theorists often talk about fundamental particles as being point-like for sake of convenience, quantum mechanics itself, with its famous uncertainty principle that makes it fundamentally and not just practically impossible to know a particle's momentum and location at the same time, in addition to contradicting Newtonian clockwork universe deterministic mechanics, also implies that even fundamental particles are in some profound way smeared at different densities over a volume of space-time (an infinite one in the extreme low density limit) rather than being truly point-like.
Quantum gravity theories overcome the singularity problem in one of two ways. Either they assume that at some scale space-time is discrete (and not necessarily perfectly local) rather than continuous and local (i.e. points in space-time can't be described with a real number coordinate system in any of its frames of reference) that reduces to general relativity in the classical scale limit, or at the quantum level, gravity is simply one more non-Abelian gauge field mediated by boson called a spin-2 graviton that is exchanged in a manner quite similar to the gluons of the strong force that interacts with mass rather than color charge and reduces to general relativity in the classical scale limit.
String theory assumes that while there are just one or two fundamental particles that manifest in all of the other fundamental particles (strings, open or closed) that those fundamental particles are not points, but instead have at least length and possibly area, in addition to retaining the uncertainty principle concept of ordinary quantum mechanics that smears fundamental particles at varying densities over a space-time region, so it has three different fixes to the gravitational singularity addressing this issue simultaneously.
Approximations And The Conjecture
Still, assume that at even very short distances that gravity behaves semi-classically in a manner analytically similar to general relativity, and that while they are fundamental that particles are sufficiently not point-like to prevent them from creating black hole singularities. The Standard Model and anything resembling it still creates lumps of very high matter-energy density interrupted by big gaps of very low matter-energy density in every case, rather than the much more homogeneous matter-energy distributions assumed for mathematical convenience in astronomy applications of general relativity. (Special relativity is built into quantum mechanics already.)
Also, assume that we are thinking about general relativity effects from a reference frame of an observer inside the fundamental particle who has the same angular momentum and linear momentum as the particle.
What does general relativity say in general about the effects of high mass-energy distributions in systems where all of the matter is at rest relative to the observer?
It says that time passes more slowly in a gravity field to the extent of that gravity field's strength according to a well defined formula. Per Wikipedia:
A common equation used to determine gravitational time dilation is derived from the Schwarzschild metric, which describes spacetime in the vicinity of a non-rotating massive spherically-symmetric object. The equation is:
t0=tf(1-2GM/rc^2)^-2=tf(1-r/r0)^-2
where
* t0 is the proper time between events A and B for a slow-ticking observer within the gravitational field,
* tf is the coordinate time between events A and B for a fast-ticking observer at an arbitrarily large distance from the massive object (this assumes the fast-ticking observer is using Schwarzschild coordinates, a coordinate system where a clock at infinite distance from the massive sphere would tick at one second per second of coordinate time, while closer clocks would tick at less than that rate),
* G is the gravitational constant,
* M is the mass of the object creating the gravitational field,
* r is the radial coordinate of the observer (which is analogous to the classical distance from the center of the object, but is actually a Schwarzschild coordinate),
* c is the speed of light, and
* r0 = 2GM/c^2 is the Schwarzschild radius of M. If a mass collapses so that its surface lies at less than this radial coordinate (or in other words covers an area of less than 4Ï€G2M2/c^4), then the object exists within a black hole.
Now, one thing that the flavor changing charged weak force currents of meson decay in mesons involving heavy quarks where CP violations is observed have in common is that the rest mass of the particles on one side of the interaction is much greater than the rest mass of the particles on other other side of the interaction.
Thus, for our observer who follows a path along a Feynman diagram from the source heavy quark to any one of the particles the result from its decay, time is going to pass more slowly before our observer starts riding a W boson than our observer does at the other end of that W boson interaction.
So, if weak interactions proceed at the same speed from the perspective of an observer in the particle or any of the particles it couples to at either end of the interaction, from the perspective of an outside observer time will be passing more slowly at the heavy end than at the light end giving rise to different interaction speeds in different directions of the interaction.
Intuitively, it makes sense that orders of magnitude heavier mass densities are going to lead to genuine CP violations and that the heavier the heaviest particle involved in the interaction, the more pronounced the CP violation will be.
It also suggests that we ought to be able to fit that model and the known rest masses of the particles involved in the decay chains of CP violating flavor changing weak force currents to the rest mass data and the time dialation effects implied for symmetric stationary masses in general relativity to infer the mass densities at each end of the interaction, or at least the curve of possible mass density differences at each end of the interaction and infer from that a semi-classical fundamental particle radius for the particles that participate in CP violating weak force interactions, addressing these in a manner mechanically quite different than the usual arbitrary empirically determined CKM matrix component approach. These semi-classical particle radii will necessarily change less markedly than mass between the particles in this model and it may very well be possible to assign a single radius to all Standard Model fermions (and even all massive Standard Model particles including the W and Z), at least as a first order approximation, by choosing points on the mass difference-radius size cover for the interactions that show CP violations that intersect. One could also try arbitrarily using the Planck length of 1.616*10^-35 meters.
Or, one could use the Compton wavelength of the particle (which is Planck's constant divided by the speed of light divided by the particle's rest mass) (for example, about 2.5 times 10^-12 meters for an electron) to see if those would fit the data. The Compton wavelength already sets the approximate effective range of a Standard Model force and its cross-section of interaction, and dovetails with the non-CP violating nature of the electromagnetic force, which makes it particularly attractive to consider as a possible radius size (perhaps adjusted by a fixed constant as is done in the case of the Bohr radius of an electron and its classical electron radius). Using Compton wavelength, which varies porportionate to 1/mass should still cause density to increase markedly with higher generation particles whose masses increase dramatically with each higher generation of a type of fermion (although I haven't done the back of napkin calculations to confirm that yet, and would have to dig up the time dialation formula - still, the calculation of that part would be elementary - it is fitting the different time rates into the weak interaction calculations that would be a bit more subtle, although probably not beyond even my abilities with a few weeks to work on it). This would further reify the heuristic intuition associated with using a Compton wavelength to determine the cross-section of interaction of a particle in the Standard Model (on the notion that this quantified the probability that it will bump into a boson in the same space near its path).
Putting Compton wavelength into the equation for r, once gets t0=tf(1-2GM^2/hc)^-2. Simplified, that is: t0=tf(1-KM^2)^-2, for K=2G/hc. I'll have to save putting particle masses appropriately converted from electron volt units, etc. (to four significant digits 1 MeV/c^2=5.914 x 10^-7 kilograms; c=2.998*10^8 meters/second; h=6.626*10^-34 kilograms*meters^2/second; the reduced Plancks constant which is h divided by 2pi, which is natural for some quantum mechanics applications, is 1.055*10^-34 kilograms*meters^2/second, and G=6.734*10^-11 meters^3/(kilogram*seconds^2); and K with ordinary non-reduced Planck's constant is 2.131*10^-24 for masses in MeV/c^2) into this equation and comparing them to observed forward v. backward rate ratios in the flavor changing weak force currents that show CP violations for a future post, or an update to this post.
For example, using Compton's wavelength, time dialation for a bottom quark which is 4200 MeV/c^2 would be about (1-3.759*10^-17)^-2=a reduction on the order of 10^-9 (almost nil). This is more like 5700 MeV/c^2 for some of the decaying B mesons that have been shown to exhibit strong CP violation.
Using Planck's length, time dialation for a bottom quark would be determined for r=1.616*10^-35 and r0=3.722*10^-30, for a total (1-4.341*10^-6)^-2=2*10^-6.
Clearly, the length would have to be much smaller to make that kind of difference. A fundamental particle scale on the order of 10^-41 meters would be necessary to get gravitational GR effects at the levels needed to fit the CP violations we observe. But, since we already have some thin evidence that space is continuous at the sub-Planck length scale, that isn't necessarily a death blow to this idea.
Benefits Of This Approach
This would give us the first directly experimentally motivated estimate of the length scale of fundamental particles or discrete distance scales, which surely shouldn't be truly point-like in a sensible theory, as opposed to merely theoretically motivated dimensional analysis used to calculate a Planck length.
This approach would also eliminate the need to add any new particles or forces or dimensions to the Standard Model to explain the observed CP violation, although it might add a new Standard Model constant to each massive particle in the Standard Model to determine its semi-classical radius if the Compton wavelength or Planck length or some other single length for all fundamental particles in the Standard Model with rest mass doesn't provide the correct time dialation effect to fit the observed CP violations.
It would also point the way towards a more general semi-classical approach to integrating general relativity and quantum mechanics at tiny length scales which is consistent with the observation made this year that by one measure at least, space-time appears to be continuous rather than discrete at a scale well below the Planck scale. String theorists could call it the characteristic string scale, and loop quantum gravity theorists could shrug and bear it. In other words, perhaps general relativity is already perfect at arbitrarily small scales and we simply need to fix a detail about particle size in quantum mechanics.
This approach would almost necessarily work to fit the data (it has a deterministic rule to fit constants with potentially many degrees of freedom, if necessary, in fundamental particle semi-classical radii), and if it found that the Compton wavelength of a single radius worked, would add no more than one constant to the Standard Model while removing the constants associated with the CP violating parameters of the CKM matrix, producing a net wash or reduction in the number of arbitary parameters of the Standard Model with better theoretical motivation.
Of course, if the radii are all over the place for different particles, or there is not consistency between different CP violations for the some particles for some reason, this approach might not deserve to be adopted.
Wednesday, August 3, 2011
Flavor-changing neutral currents and Z boson interactions recapped
This is a background post that includes experimental data current as of results from March 2011 from the DZero experiment. It looked for "flavour-changing neutral current decays of top quark pairs, where about 30,000 of the latter have been produced in something like 300 quadrillion 1.96 TeV proton-antiproton collisions" and came up empty handed. Instead, "top quarks decay almost exclusively into bottom quarks and W bosons" without forming mesons (two quark composite particles) or baryons (three quark composite particles).
The bottom line is that the W bosons, which are charged weak force carryiing particles (they come in charge +1 and charge -1 versions and are antiparticles of each other) can change flavor (e.g. when a charm quark emits a W boson, it could turn into a down quark). But, the roughly 1/8th heavier charge zero version of the W boson called the Z boson (sometimes written with a superscript zero) does not play a part in flavor changing interactions. The starting and ending point of Z boson interactions have the same flavor. If a charm quark emits a Z boson it will remain a Z boson. If a Z boson did bring about a flavor changing interaction we would call it a flavor changing neutral current (FCNC).
There are some speculative theories about why this doesn't happen, such as the GIM mechanism (an acronymn of the surnames of the theorists who came up with it and simultaneously predicted the charm quark). But, whatever the reason, we have been smashing atoms since we discovered the Z boson in 1983 and we still haven't caught Z bosons engaged in flavor changing interactions, 28 years later. There are some multi-step processes that involve W bosons that superficially look like a flavor changing Z boson interaction would, but the theory of electroweak interactions is exceedingly precise on this point, so our ability to separate this background from the signal of a FCNC, and if FCNC's exist they must be exceedingly rare.
In other words, the only thing that can turn a particle into another particle of a different flavor as it interacts with it is a W boson. Strong nuclear force interactions (via gluons), electromagnetic interactions (via photons) and gravity (via gravitons or the geometry of space-time) don't do this trick. Neither does the Z boson. Also, it is worth noting that neither the W boson nor the Z boson change strong nuclear force color charge. W bosons do change the charge of the particles that they interact with by a factor of one plus or minus, and do convert energy into rest mass, and convert rest mass into energy (although W boson interactions conserve combined mass-energy).
What does a Z boson do? It is emitted from or absorbed by a quark or lepton. And, it decays into a fermion and its antiparticle in very precise proportions, an exact formula for which neatly matches the experimental data, although these proportions are constrained by the amount of matter-energy the Z boson has to start with (a low energy Z boson can't create higher mass pairs when it decays). Thus, "a quark or a lepton emits or absorbs a neutral Z boson. For example: e => e +Z
Like the W boson, the Z boson also decays rapidly, for example [if it has enough mass-energy]:
Z => b + anti-b."
But, a muon cannot emit a Z boson and as a result become an electron. The emission or absorbsion of a Z boson does not change the flavor of the emitting or absorbing particle.
This is worked out with more rigor than a blog post can here.
In contrast, "W bosons can decay to a lepton and neutrino or to an up-type or down type quark." Up-type quarks always decay into down-type quarks via the W boson and down-type quarks always decay into up-type quarks via the W boson. Neutrino oscillation is also a W boson driven process in the Standard Model.
Implications
The lack of FCNCs turns out to be a big deal because a large class of theories that otherwise reproduce the Standard Model in places where it has been experimentally confirmed, and extend it in places where experimental data provided no data or suggests a possible deviation from the Standard Model, have flavor-changing neutral currents that aren't found in reality. This law of physics, like the observed absence of proton decay and the observed absence of magnetic monopoles, rules out many otherwise plausible theoretical models.
The experiments don't demand that the number of FCNC interactions be zero, but they are consistent with zero (as are proton decay rates and the number of observed magnetic monopoles which have never been observed in very large data sets), and it is tempting to assume that they are exactly zero rather than very small but not quite zero in frequency, without powerful experimental motivations from some other line of evidence for doing otherwise.
Weak force interaction data also rule out fourth or higher generation particles in which neutrinos have a mass less than half of the Z boson. If such particles existed, the weak force decay rules would predict that we would have seen some of them by now. This means that a fourth generation neutrino, if one exists, is on the order of one thousand times as heavy as a third generation neutrino (if not heavier).
In electroweak unification theory, a more fundamental neutrally charged W boson and a neutrally charged B boson linearly combine to give rise to the Z and the photon, according to a two by two matrix based on the sines and cosines of what is called the the mixing angle theta sub W, a feature of the theory that explains why the photon and Z have different masses than the W+ and W- bosons in the amount seen experimentally. The W and Z also subsume two of the three predicted Standard Model Higgs bosons, leaving only one of them bare of other particles.
The bottom line is that the W bosons, which are charged weak force carryiing particles (they come in charge +1 and charge -1 versions and are antiparticles of each other) can change flavor (e.g. when a charm quark emits a W boson, it could turn into a down quark). But, the roughly 1/8th heavier charge zero version of the W boson called the Z boson (sometimes written with a superscript zero) does not play a part in flavor changing interactions. The starting and ending point of Z boson interactions have the same flavor. If a charm quark emits a Z boson it will remain a Z boson. If a Z boson did bring about a flavor changing interaction we would call it a flavor changing neutral current (FCNC).
There are some speculative theories about why this doesn't happen, such as the GIM mechanism (an acronymn of the surnames of the theorists who came up with it and simultaneously predicted the charm quark). But, whatever the reason, we have been smashing atoms since we discovered the Z boson in 1983 and we still haven't caught Z bosons engaged in flavor changing interactions, 28 years later. There are some multi-step processes that involve W bosons that superficially look like a flavor changing Z boson interaction would, but the theory of electroweak interactions is exceedingly precise on this point, so our ability to separate this background from the signal of a FCNC, and if FCNC's exist they must be exceedingly rare.
In other words, the only thing that can turn a particle into another particle of a different flavor as it interacts with it is a W boson. Strong nuclear force interactions (via gluons), electromagnetic interactions (via photons) and gravity (via gravitons or the geometry of space-time) don't do this trick. Neither does the Z boson. Also, it is worth noting that neither the W boson nor the Z boson change strong nuclear force color charge. W bosons do change the charge of the particles that they interact with by a factor of one plus or minus, and do convert energy into rest mass, and convert rest mass into energy (although W boson interactions conserve combined mass-energy).
What does a Z boson do? It is emitted from or absorbed by a quark or lepton. And, it decays into a fermion and its antiparticle in very precise proportions, an exact formula for which neatly matches the experimental data, although these proportions are constrained by the amount of matter-energy the Z boson has to start with (a low energy Z boson can't create higher mass pairs when it decays). Thus, "a quark or a lepton emits or absorbs a neutral Z boson. For example: e => e +Z
Like the W boson, the Z boson also decays rapidly, for example [if it has enough mass-energy]:
Z => b + anti-b."
But, a muon cannot emit a Z boson and as a result become an electron. The emission or absorbsion of a Z boson does not change the flavor of the emitting or absorbing particle.
This is worked out with more rigor than a blog post can here.
In contrast, "W bosons can decay to a lepton and neutrino or to an up-type or down type quark." Up-type quarks always decay into down-type quarks via the W boson and down-type quarks always decay into up-type quarks via the W boson. Neutrino oscillation is also a W boson driven process in the Standard Model.
Implications
The lack of FCNCs turns out to be a big deal because a large class of theories that otherwise reproduce the Standard Model in places where it has been experimentally confirmed, and extend it in places where experimental data provided no data or suggests a possible deviation from the Standard Model, have flavor-changing neutral currents that aren't found in reality. This law of physics, like the observed absence of proton decay and the observed absence of magnetic monopoles, rules out many otherwise plausible theoretical models.
The experiments don't demand that the number of FCNC interactions be zero, but they are consistent with zero (as are proton decay rates and the number of observed magnetic monopoles which have never been observed in very large data sets), and it is tempting to assume that they are exactly zero rather than very small but not quite zero in frequency, without powerful experimental motivations from some other line of evidence for doing otherwise.
Weak force interaction data also rule out fourth or higher generation particles in which neutrinos have a mass less than half of the Z boson. If such particles existed, the weak force decay rules would predict that we would have seen some of them by now. This means that a fourth generation neutrino, if one exists, is on the order of one thousand times as heavy as a third generation neutrino (if not heavier).
In electroweak unification theory, a more fundamental neutrally charged W boson and a neutrally charged B boson linearly combine to give rise to the Z and the photon, according to a two by two matrix based on the sines and cosines of what is called the the mixing angle theta sub W, a feature of the theory that explains why the photon and Z have different masses than the W+ and W- bosons in the amount seen experimentally. The W and Z also subsume two of the three predicted Standard Model Higgs bosons, leaving only one of them bare of other particles.
Particle and Atomic Physics In A Nutshell
If you are looking for a nice one page diagram that sets forth the major particles, forces, composite particles and quantum theories that have been observed in a way the compactly illustrates their relationships to each other (e.g. as a vocabularly builder or educational tool), you could do worse than the colorful graphic found here.
Tuesday, August 2, 2011
Interesting SM4 Paper
Enrico Lunghi and Amarjiit Soni, "Demise of CKM & its aftermath" (June 27, 2011):
The main motivation for SM4 is excessive CP violation in bottom to strange quark situations which additional CP violating phases in SM4 can fit. The CP violating sin2 beta parameter estimated to be about 0.85 in the Standard Model is closer to 0.66 and may even be a bit lower. The hierarchy problem disappears in SM4 (eliminating one of the biggest justifications for SUSY) as does the question of the suppression of flavor changing neutral current processes, which it explains.
Also attractively, given the apparent lack of a light Higgs signal from LHC, the "[n]atural mass scale for a Higgs particle in SM4, where the heavy quarks are geared towards EW symmetry breaking, is around [twice the fourth generation bottom quark mass]. Such a heavy Higgs would of course have very clean decays to H => ZZ. Electroweak precision tests do not rule out the existence of a 4th generation though they restrict the mass splitting between the 4th generation doublet (t'; b') of quarks to be less than around 75 GeV. This requires some 10% degeneracy in their masses. . . Furthermore LEP experiments require that the 4th generation neutral lepton has to be rather heavy [greater than about half the Z particle mass]; this begs the question as to why there should be such a huge disparity with the three almost massless neutrinos of the conventional SM3. . . . experimental searches for quarks (t', b') of the 4th generation have already been underway at Fermilab leading to a lower bound of around 350 GeV. . . . It is expected that after several years of efforts, LHC should be able to find these quarks or put a bound close to a TeV."
In the SM4 model the Higgs boson mass would significantly exceed 700 GeV, which is both large enough not to be ruled out by experiment and small enough to be within the realm of what experiment could discovery in the medium term future.
The heavy fourth generation neutrino is attractive, of course, because it would provide a dark matter candidate without the necessity of inventing a new class of fermion that behaves very much like a neutrino.
Using firmrmly established experimental inputs . . . along with corresponding lattice matrix elements which have been well studied and are in full QCD such as BK, SU3 breaking ratio, BBs and in particular without using Vub or the pseudoscalar decay constants fBd or fBs from the lattice, we show that the CKM-paradigm now appears to be in serious conflict with the data. Specifically the SM predicted value of sin 2 beta seems too high compared to direct experimental measured value by over 3 sigma. Furthermore, our study shows that new physics predominantly effects B-mixings . . . and not primarily in kaon-mixing . . . . Model independent operator analysis suggests the scale of underlying new physics, accompanied by a BSM CP-odd phase, responsible for breaking of the SM is less than a few TeV, possibly as low as a few hundred GeV. . . . While SM with 4th generation (SM4) is a very simple way to account for the observed anomalies, SM4 is also well motivated due to its potential role in dynamical electroweak symmetry breaking via condensation of heavy quarks and in baryogenesis.
The main motivation for SM4 is excessive CP violation in bottom to strange quark situations which additional CP violating phases in SM4 can fit. The CP violating sin2 beta parameter estimated to be about 0.85 in the Standard Model is closer to 0.66 and may even be a bit lower. The hierarchy problem disappears in SM4 (eliminating one of the biggest justifications for SUSY) as does the question of the suppression of flavor changing neutral current processes, which it explains.
Also attractively, given the apparent lack of a light Higgs signal from LHC, the "[n]atural mass scale for a Higgs particle in SM4, where the heavy quarks are geared towards EW symmetry breaking, is around [twice the fourth generation bottom quark mass]. Such a heavy Higgs would of course have very clean decays to H => ZZ. Electroweak precision tests do not rule out the existence of a 4th generation though they restrict the mass splitting between the 4th generation doublet (t'; b') of quarks to be less than around 75 GeV. This requires some 10% degeneracy in their masses. . . Furthermore LEP experiments require that the 4th generation neutral lepton has to be rather heavy [greater than about half the Z particle mass]; this begs the question as to why there should be such a huge disparity with the three almost massless neutrinos of the conventional SM3. . . . experimental searches for quarks (t', b') of the 4th generation have already been underway at Fermilab leading to a lower bound of around 350 GeV. . . . It is expected that after several years of efforts, LHC should be able to find these quarks or put a bound close to a TeV."
In the SM4 model the Higgs boson mass would significantly exceed 700 GeV, which is both large enough not to be ruled out by experiment and small enough to be within the realm of what experiment could discovery in the medium term future.
The heavy fourth generation neutrino is attractive, of course, because it would provide a dark matter candidate without the necessity of inventing a new class of fermion that behaves very much like a neutrino.
Another Standard Model Deviation Looking Like An Experimental Fluke
Something called the diject mass bump observed by the CDF high energy physics experiment has not been replicated by its fellow experiment at the same facility, DZero, and has also not been replicated (yet, the data are too thin so far to be definitive) at the ATLAS experiment at the large hadron collider (LHC).
This adds to the ever growing list of hints of beyond the standard model physics that appeared in early data sets in the past few years but have later proven to be statistical flukes or experimental error. Mass asymmetries between the top and anti-top quark, and the anomalous magnetic moment of the muon (muon g-2), also appear to be headed that way, as do a number of ressonances that might have indicated beyond the standard model particles. Efforts to probe for a composite nature of the quark have pushed previous boundaries on quark size down by a factor of three or four this year making the quark appear more and more point-like.
For that matter, there has also been no success in identifying a ressonance of the within the standard model Higgs boson, although there is a narrow mass window where experiments can't definitively rule it out.
Rather than finding experiments that point to more than the Standard Model, we are finding less physics than the Standard Model allows.
One area of beyond the standard model physics supported by experimental data that does seem to be holding up in the face of growing data sets is the existence of larger than predicted CP violation in heavy flavor quark and lepton decay, experimental results that have pushed the ability of a parameterized matrix of weak force transitions to the breaking point or beyond consistent with the margins of error of the various experiments done to date. Prior readers of this blog will know that one of the least radical ways to resolve this would be to discover another very high mass generation of fermions that otherwise are precisely like their existing Standard Model counterparts.
Another, which is a single data point, but a potentially important one, is that the measured radius of muonic hydrogen is not in line with theoretical predictions to the tune of a five sigma deviation from theoretical expectation, although this could have some subtle sources of error in the constants that go into making the theoretical prediction. This is a result that basically no one expected, which makes it particularly interesting. The absence of any unexpected finding in experiments with "anti-protonic helium" which has a similar methodology is discouraging to the cause of making sense of the muonic hydrogen results with any coherent theory, as have been suggestions that there may have been minor calculation errors in the first estimate. Some fumblings in the dark to look for a cause of this effect were described in a February 2011 workshop and another one in March of this year and also here. A paper proposing new physics to explain the result (not very convincingly) was published in May.
FWIW, the most plausible resolutions of this quandry in my mind are the possibility that the uncertainty in the component constants of the calculation are off in some way, leading to an overestimation of the precision of the theoretical calculation.
Another possiblity that comes to mind is that the amplitude for a muon to become a tau (third generation electron) is underestimated (a 2003 paper suggested that it might be higher than naiively expected, with the best available data coming from tauon decay), and that the measured result represents a superposition of muon and tau states cause the effects of a more massive negatively charged lepton circling the proton (a tau is almost double the mass of a proton) to be exaggerated. The error is about 4% from the predicted value, the tau is much heavier than the muon, and the PMNS matrix values aren't known to terribly great accuracy, so what looks like it should be a disregardable term might be materially greater than expected, although I am not competent to do even a back of napkin numerical impact of the transition probability that would be needed. A 2010 paper has looked at the impact of a fourth generation of leptons on these values. The amplitude for electrons to remain electrons so dominates the PMNS coeffecients that flavor changing phenomena are probably virtually irrelevant in hydrogen radius calculations because it has a more than 99% factor to stay an electron. But, coefficients for muons and taus are much more similar to each other (within a factor of two or so) than the electron coefficient is to either (at least an order of magnitude larger), so this factor which is immaterial in the hydrogen radius calculation for ordinary hydrogen may matter in the muonic hydrogen radius calculation. (See also here for the state of estimates of PMNS coefficient values.)
(This is probably as good a place as any to mention as a footnote that we still don't understand the cause of the Koide formula, which states that the sum of the charged lepton masses divided by the square of the sum of their square roots is equal to precisely two-thirds, something that has been shown empirically to be "0.666659(10)" and was used to predict the tau's mass. Some interesting speculation on what this could mean and how a similar formula might be applied to neutrino masses is found here. Carl Brannen has a discussion linked to in that post from 2006, regarding the neutrino generalization, which received a little bit of academic notice including papers by none other than Koide himself, that is also interesting as is a late 2007 blog post of his in the same vein. Whether or not Brannen is right, he is asking the kinds of questions that more academic theoretical physicists should be asking and making plausible suggestions that derve fuller airing and investigation.)
A third possiblity is that we are seeing a quantum gravity effect, something that was proposed as a possibility back in 2006, long before this experiment was conducted.
Implications For Dark Matter Theories
In addition to leaving high energy physicists looking like i dotting, t crossing technicians who write boring papers that tell us nothing new, this also impacts astronomers, cosmologists and gravity theorists, because one after another potential dark matter candidate is being ruled out by their failure to appear in direct searchers. Prevailing dark matter theories require immensive amounts of stable non-baryonic matter with very low interaction cross-sections (rather akin to neutrinos in that regard). But, the only meta-stable candidates with less than about 800 GeV of mass that is seriously in the running at this point would be some form of right handed or sterile fourth generation neutrino. Moreover, most of the theoretically conceptualized greater than 800 GeV mass, low interaction cross-section particles would rapidly decay. Even if SUSY is correct, most predictions assume that only a single kind of SUSY particle (the lighest non-charged supersymmetric particle) would be stable. Yet, a non-charged lightest supersymmetric particle, like a neutralino, now apparently constrained by LHC to be 800 GeV of mass or more by LHC, might be ruled out as a dark matter candidate by direct experiments even if we could find that one existed.
Direct astronomy oriented searches for dark matter particles have also largely come up empty handed although one did hint at a possible seasonal variation that could be a signal of a dark matter particle (although this is not being confirmed by similar experiments of the same kind that saw a signal) and there have been some less than statistically significant possible hints in the data that dark matter might be interacting weakly and leaving a trace. Their parameter space exclusions seem to naiively favor mass ranges that existing atom smashers should have discovered already, a seven or more times lighter than a top quark, which has been discovered, and to rule out dark matter particles of 800 GeV of mass or more.
Of course, charged fermions are easier to spot in a detector than those that are only weakly interacting; a slow moving heavy particle with neutral charge can masquerade as one or more fast moving neutrinos or might not be produced in those experiments at all because they don't interact with the weak force that is associated with the decay chains seen in these experiments.
Combining the direct dark matter searches of astronomers with the higher energy physics findings produces overlapping exclusion zones for dark matter candidates that both would have any possibility of observing, something that makes previously out of left field concepts, like a massive graviton or a dark matter candidate that doesn't interact with the weak force, look more attractive. It also puts pressure on scientists to identify gravity modifications or improved general relativity calculations that can fit the data that gave rise to dark matter theory (or at least enough of a modification to end the need to find a dark matter particle that has been ruled out).
From a theoretical physics perspective, the mere experimental determination that any beyond the standard physics particles that could be dark matter candidates are excluded, even if a resolution of the dark matter issue is not reached, undercuts one of the major motivations for beyond the standard model physics. The less there is for beyond the standard model physics to explain, there more doubt is cast of the need for it at all, and the more likely it is that whatever is needed to modify the standard model is going to be subtle and boring.
This adds to the ever growing list of hints of beyond the standard model physics that appeared in early data sets in the past few years but have later proven to be statistical flukes or experimental error. Mass asymmetries between the top and anti-top quark, and the anomalous magnetic moment of the muon (muon g-2), also appear to be headed that way, as do a number of ressonances that might have indicated beyond the standard model particles. Efforts to probe for a composite nature of the quark have pushed previous boundaries on quark size down by a factor of three or four this year making the quark appear more and more point-like.
For that matter, there has also been no success in identifying a ressonance of the within the standard model Higgs boson, although there is a narrow mass window where experiments can't definitively rule it out.
Rather than finding experiments that point to more than the Standard Model, we are finding less physics than the Standard Model allows.
One area of beyond the standard model physics supported by experimental data that does seem to be holding up in the face of growing data sets is the existence of larger than predicted CP violation in heavy flavor quark and lepton decay, experimental results that have pushed the ability of a parameterized matrix of weak force transitions to the breaking point or beyond consistent with the margins of error of the various experiments done to date. Prior readers of this blog will know that one of the least radical ways to resolve this would be to discover another very high mass generation of fermions that otherwise are precisely like their existing Standard Model counterparts.
Another, which is a single data point, but a potentially important one, is that the measured radius of muonic hydrogen is not in line with theoretical predictions to the tune of a five sigma deviation from theoretical expectation, although this could have some subtle sources of error in the constants that go into making the theoretical prediction. This is a result that basically no one expected, which makes it particularly interesting. The absence of any unexpected finding in experiments with "anti-protonic helium" which has a similar methodology is discouraging to the cause of making sense of the muonic hydrogen results with any coherent theory, as have been suggestions that there may have been minor calculation errors in the first estimate. Some fumblings in the dark to look for a cause of this effect were described in a February 2011 workshop and another one in March of this year and also here. A paper proposing new physics to explain the result (not very convincingly) was published in May.
FWIW, the most plausible resolutions of this quandry in my mind are the possibility that the uncertainty in the component constants of the calculation are off in some way, leading to an overestimation of the precision of the theoretical calculation.
Another possiblity that comes to mind is that the amplitude for a muon to become a tau (third generation electron) is underestimated (a 2003 paper suggested that it might be higher than naiively expected, with the best available data coming from tauon decay), and that the measured result represents a superposition of muon and tau states cause the effects of a more massive negatively charged lepton circling the proton (a tau is almost double the mass of a proton) to be exaggerated. The error is about 4% from the predicted value, the tau is much heavier than the muon, and the PMNS matrix values aren't known to terribly great accuracy, so what looks like it should be a disregardable term might be materially greater than expected, although I am not competent to do even a back of napkin numerical impact of the transition probability that would be needed. A 2010 paper has looked at the impact of a fourth generation of leptons on these values. The amplitude for electrons to remain electrons so dominates the PMNS coeffecients that flavor changing phenomena are probably virtually irrelevant in hydrogen radius calculations because it has a more than 99% factor to stay an electron. But, coefficients for muons and taus are much more similar to each other (within a factor of two or so) than the electron coefficient is to either (at least an order of magnitude larger), so this factor which is immaterial in the hydrogen radius calculation for ordinary hydrogen may matter in the muonic hydrogen radius calculation. (See also here for the state of estimates of PMNS coefficient values.)
(This is probably as good a place as any to mention as a footnote that we still don't understand the cause of the Koide formula, which states that the sum of the charged lepton masses divided by the square of the sum of their square roots is equal to precisely two-thirds, something that has been shown empirically to be "0.666659(10)" and was used to predict the tau's mass. Some interesting speculation on what this could mean and how a similar formula might be applied to neutrino masses is found here. Carl Brannen has a discussion linked to in that post from 2006, regarding the neutrino generalization, which received a little bit of academic notice including papers by none other than Koide himself, that is also interesting as is a late 2007 blog post of his in the same vein. Whether or not Brannen is right, he is asking the kinds of questions that more academic theoretical physicists should be asking and making plausible suggestions that derve fuller airing and investigation.)
A third possiblity is that we are seeing a quantum gravity effect, something that was proposed as a possibility back in 2006, long before this experiment was conducted.
Implications For Dark Matter Theories
In addition to leaving high energy physicists looking like i dotting, t crossing technicians who write boring papers that tell us nothing new, this also impacts astronomers, cosmologists and gravity theorists, because one after another potential dark matter candidate is being ruled out by their failure to appear in direct searchers. Prevailing dark matter theories require immensive amounts of stable non-baryonic matter with very low interaction cross-sections (rather akin to neutrinos in that regard). But, the only meta-stable candidates with less than about 800 GeV of mass that is seriously in the running at this point would be some form of right handed or sterile fourth generation neutrino. Moreover, most of the theoretically conceptualized greater than 800 GeV mass, low interaction cross-section particles would rapidly decay. Even if SUSY is correct, most predictions assume that only a single kind of SUSY particle (the lighest non-charged supersymmetric particle) would be stable. Yet, a non-charged lightest supersymmetric particle, like a neutralino, now apparently constrained by LHC to be 800 GeV of mass or more by LHC, might be ruled out as a dark matter candidate by direct experiments even if we could find that one existed.
Direct astronomy oriented searches for dark matter particles have also largely come up empty handed although one did hint at a possible seasonal variation that could be a signal of a dark matter particle (although this is not being confirmed by similar experiments of the same kind that saw a signal) and there have been some less than statistically significant possible hints in the data that dark matter might be interacting weakly and leaving a trace. Their parameter space exclusions seem to naiively favor mass ranges that existing atom smashers should have discovered already, a seven or more times lighter than a top quark, which has been discovered, and to rule out dark matter particles of 800 GeV of mass or more.
Of course, charged fermions are easier to spot in a detector than those that are only weakly interacting; a slow moving heavy particle with neutral charge can masquerade as one or more fast moving neutrinos or might not be produced in those experiments at all because they don't interact with the weak force that is associated with the decay chains seen in these experiments.
Combining the direct dark matter searches of astronomers with the higher energy physics findings produces overlapping exclusion zones for dark matter candidates that both would have any possibility of observing, something that makes previously out of left field concepts, like a massive graviton or a dark matter candidate that doesn't interact with the weak force, look more attractive. It also puts pressure on scientists to identify gravity modifications or improved general relativity calculations that can fit the data that gave rise to dark matter theory (or at least enough of a modification to end the need to find a dark matter particle that has been ruled out).
From a theoretical physics perspective, the mere experimental determination that any beyond the standard physics particles that could be dark matter candidates are excluded, even if a resolution of the dark matter issue is not reached, undercuts one of the major motivations for beyond the standard model physics. The less there is for beyond the standard model physics to explain, there more doubt is cast of the need for it at all, and the more likely it is that whatever is needed to modify the standard model is going to be subtle and boring.
Adventures In Chemicals The Affect The Brain And Seasonal Birth Effects
I've abstracted a hodgepodge of interesting new research studies on the impact of chemicals and birthdays on mental health. We a finally reaching the frontier where the actual biological mechanism behind mental health conditions long believed to have a biological basis are understood in a meaningful fashion with clinical applications.
Cortisol hormone response patterns linked to temperament in toddlers
Cortisol responses to stress in toddlers reflect their temperaments and may also have significant environmental responses. Personality traits which otherwise seem to have only suggestive oppositions to each other seem to have a biological root as different dimensions of cortisol responses to stress. In particular, anxiety and depression may be the opposite side of the coin the same trait that at the other extreme may be associated with ADHD. It wouldn't overstate the matter to infer that the Big Five personality trait conscientiousness may also be linked to this tendency that is present in very early childhood.
Previous research has focused more on neurotransmitters and general stimulants in these conditions.
Dopamine flows from anticipation of reward, not the reward itself.
From here.
Drug Addition Linked To Salt Appetite System
From here.
Ketamine Has Different Roles At Different Doses
Ketamine is finding new applications in both legal and illegal applications.
From here.
A small trial reported in 2010 found Ketamine to be safe and effective in treating treatment-resistant bipolar patients, suggesting that it acts on a different mechanism than existing depression treatments. Unlike traditional anti-depressants, whose efficacy has been seriously questioned as being little more than placebo effect in a significant class of patients treated with them, Ketamine's effect is so rapid and pronounced that its short term effectiveness is beyond question, although its tendency to be associated with mild psychiotic side effects is a concern.
British drug enforcement authorities have seen increased abuse of ketamine:
Hallucinating Computers
Efforts to create neural network computer models of the brain's circuits for processing language in an effort to understand schizophrenic auditory hallucinations have managed to reproduce the phenomena of coherent auditory hallucinations (i.e. hearing voices) by both of two different mechanisms suspected to be a work in this phenomena in the real world.
The two different models that were both supported in the computerized neural network were as follows:
Birth Season Effects On Mental Health
A causal mechanism isn't obvious, but some mental health conditions so seasonal effects.
Meanwhile:
The study lacked the means to discern if conception or some later point in pregnancy was the source of the vulnerability.
Cortisol hormone response patterns linked to temperament in toddlers
Cortisol responses to stress in toddlers reflect their temperaments and may also have significant environmental responses. Personality traits which otherwise seem to have only suggestive oppositions to each other seem to have a biological root as different dimensions of cortisol responses to stress. In particular, anxiety and depression may be the opposite side of the coin the same trait that at the other extreme may be associated with ADHD. It wouldn't overstate the matter to infer that the Big Five personality trait conscientiousness may also be linked to this tendency that is present in very early childhood.
Is your kid a "dove" -- cautious and submissive when confronting new environments, or perhaps you have a "hawk" -- bold and assertive in unfamiliar settings? . . .
Children exposed to high levels of interparental aggression at home showed different reactions to [a staged] telephone quarrel. Doves with parents who fought violently produced elevated levels of cortisol, a hormone that is thought to increase a person's sensitivity to stress. Hawks from such stressful home environments put the breaks on cortisol production, which is regarded as a marker for diminishing experiences of danger and alarm.
Heightened cortisol levels characteristic of the doves were related to lower attention problems but also put them at risk for developing anxiety and depression over time. By contrast, the lower cortisol levels for hawks in aggressive families were associated with lower anxiety problems; however, at the same time, these children were more prone to risky behavior, including attention and hyperactivity problems.
Previous research has focused more on neurotransmitters and general stimulants in these conditions.
Dopamine flows from anticipation of reward, not the reward itself.
The treatment of psychiatric conditions like depression or schizophrenia often revolves around regulating monoamine neurotransmitters like serotonin, norepinephrine and dopamine.
Dopamine is an important neurotransmitter that functions in a lot of behaviors and reactions, such as movement, lactation, aggression, fear, etc. In diseases like Parkinson, dopamine levels lower and movement becomes uncontrolled. In other diseases like schizophrenia, either dopamine levels are high or response to dopamine is higher, and paranoia & hallucinations manifest. Treating schizophrenia involves blocking dopamine receptors. As you can imagine, a common side effect of antipsychotics is movement disorders — or Parkinsonism. . . .
Our cultural and behavioral predisopostions ultimately boil down to chemicals in our brain interacting and stimulating other areas. One of the most important functions of dopamine is in the reward system of the brain, an area called the nucleus accumbens that primes pleasurable behavior to repeat, such as sex, eating, and drugs. . . .
Robert Sapolsky of Stanford Neurology makes the distinction between how dopamine levels rise in the anticipation of pleasure and not as a response to pleasure.
From here.
Drug Addition Linked To Salt Appetite System
[T]he gene patterns activated by stimulating an instinctive behavior, salt appetite, [a]re the same groups of genes regulated by cocaine or opiate (such as heroin) addiction.
"[B]locking addiction-related pathways . . . powerfully interfere[s] with sodium appetite. . . . [The] findings . . . could lead to a new understanding of addictions and the detrimental consequences when obesity-generating foods are overloaded with sodium. . . . Though instincts like salt appetite are basically genetic neural programs, they may be substantially changed by learning and cognition . . . Once the genetic program is operating, experiences that are part of the execution of the program become embodied in the overall patterns of an individual's behavior, and some scientists have theorized that drug addiction may use nerve pathways of instinct. . . . one classic instinct, the hunger for salt, is providing neural organization that subserves addiction to opiates and cocaine."
From here.
Ketamine Has Different Roles At Different Doses
Ketamine is finding new applications in both legal and illegal applications.
The anesthetic ketamine works against depression by quickly boosting levels of a brain compound that has been linked to the condition . . . [which] may lead to highly effective and fast-acting antidepressants that provide relief within hours instead of weeks. . . . Traditional antidepressants can be effective but often take weeks or months to improve symptoms. . . . “Here is increasing evidence that you can go more directly at the target, and that’s maybe why you get more of a rapid antidepressant effect.”
Mice receiving a single injection of ketamine showed fewer signs of depression just half an hour after the shot, and they continued to show multiple signs of reduced depression for a week. . . .
At high doses, ketamine renders a person unconscious. At lower doses, the drug can induce euphoria, hallucinations and out-of-body experiences, properties that make “Special K” a popular drug of abuse. . . . the study . . . used low doses that wouldn’t induce psychotic effects.
They found that ketamine kicks off a series of biochemical changes in the brain that culminate in the production of a protein called BDNF. Low BDNF levels have been linked to depression. . . . mice genetically engineered to be unable to produce BDNF didn’t respond to ketamine.
From here.
A small trial reported in 2010 found Ketamine to be safe and effective in treating treatment-resistant bipolar patients, suggesting that it acts on a different mechanism than existing depression treatments. Unlike traditional anti-depressants, whose efficacy has been seriously questioned as being little more than placebo effect in a significant class of patients treated with them, Ketamine's effect is so rapid and pronounced that its short term effectiveness is beyond question, although its tendency to be associated with mild psychiotic side effects is a concern.
British drug enforcement authorities have seen increased abuse of ketamine:
Once seen as a drug exclusively for the rave and dance scene, its popularity is now growing among Britain's middle-class users due to its price – a gram of ketamine costs £20, half as much as the same amount of cocaine – and the fact that it is seen as a "safe" and "clean" drug. . .
a survey carried out by Professor David Nutt, the chairman of the Government's drug advisory panel, ranks the class C drug as the sixth most dangerous illegal drug available – more harmful than Ecstasy and cannabis. The mistaken belief that the substance is risk-free is encouraging more young people to try ketamine and to take it in increasingly higher doses. . . . it can cause heart or lung failure and point to the fact that it has been linked to 23 deaths between 1993 and 2006. In 2006 it was classified as a class C drug [in the U.K.] . . . the drug, which can be snorted, swallowed, injected and even smoked, . . . [had] an estimated 60,000 users [in the U.K.] between 1998 and 2000 . . . [and] about 113,000 in 2008. . . .
Originally used to treat injured soldiers in Vietnam, ketamine is most commonly used now as a horse tranquilliser. It has also been experimented with to treat depression and alcohol and heroin addiction. It was classified as an illegal drug in 2006 by the UK Government. It is usually sold in powder or liquid form for about £20 per gram. Unlike cocaine and heroin, it is not physically addictive, but, like cannabis and Ecstasy, it is psychologically addictive.
David first tried ketamine as a 20-year-old student at university in London. Now a 27-year-old marketing executive, living in Shoreditch, east London, he still takes the drug once a month. "I see it as a fun, sociable drug," he said. "I do it at house parties or if I'm having a big night out. I used to do cocaine, but I suppose I gradually replaced coke with ket. Coke is much more expensive and it generally makes everyone very loud and aggressive. Ket is different. It costs less and you use it in smaller quantities so it lasts a lot longer. The feeling you get is different too. It makes you feel anaesthetised to your worries. You forget about your normal life and everything is euphoric. Sometimes I've had bad trips, but I've never felt angry when on ketamine. I think it is a lot safer too. I've read it can have long-term effects on your health, but it doesn't seem as dangerous as cocaine. When on coke I used to feel my heart pounding and it didn't feel right. The other reason I changed is because of the classification. I've got a proper job and a career and I don't want to lose that. Ketamine is a class C drug so if I get caught I'm probably only going to get a slap on the wrist."
Hallucinating Computers
Efforts to create neural network computer models of the brain's circuits for processing language in an effort to understand schizophrenic auditory hallucinations have managed to reproduce the phenomena of coherent auditory hallucinations (i.e. hearing voices) by both of two different mechanisms suspected to be a work in this phenomena in the real world.
Hearing voices is a hallmark of schizophrenia and other psychotic disorders, occurring in 60-80% of cases. These voices are typically identified as belonging to other people and may be voicing the person’s thoughts, commenting on their actions or ideas, arguing with each other or telling the person to do something. Importantly, these auditory hallucinations are as subjectively real as any external voices. They may in many cases be critical or abusive and are often highly distressing to the sufferer.
However, many perfectly healthy people also regularly hear voices – as many as 1 in 25 according to some studies, and in most cases these experiences are perfectly benign. In fact, we all hear voices “belonging to other people” when we dream – we can converse with these voices, waiting for their responses as if they were derived from external agents. Of course, these percepts are actually generated by the activity of our own brain, but how?
The two different models that were both supported in the computerized neural network were as follows:
There are two major hypotheses that were modelled: the first is that networks in schizophrenia are “over-pruned”. This fits with a lot of observations, including neuroimaging data showing reduced connectivity in the brains of people suffering with schizophrenia. It also fits with the age of onset of the florid expression of this disorder, which is usually in the late teens to early twenties. This corresponds to a period of brain maturation characterised by an intense burst of pruning of synapses – the connections between neurons.
In schizophrenia, the network may have fewer synapses to begin with, but not so few that it doesn’t work well. This may however make it vulnerable to this process of maturation, which may reduce its functionality below a critical threshold. Alternatively, the process of synaptic pruning may be overactive in schizophrenia, damaging a previously normal network. (The evidence favours earlier disruptions).
The second model involves differences in the level of dopamine signalling in these circuits. Dopamine is a neuromodulator – it alters how neurons respond to other signals – and is a key component of active perception. It plays a particular role in signalling whether inputs match top-down expectations derived from our learned experience of the world. There is a wealth of evidence implicating dopamine signalling abnormalities in schizophrenia, particularly in active psychosis. Whether these abnormalities are (i) the primary cause of the disease, (ii) a secondary mechanism causing specific symptoms (like psychosis), or (iii) the brain attempting to compensate for other changes is not clear.
Birth Season Effects On Mental Health
A causal mechanism isn't obvious, but some mental health conditions so seasonal effects.
Anorexia nervosa is more common among people born in the spring. . . . [Researchers] found an excess of anorexia births between March and June, and a deficit from September to October. . . . A number of previous studies have found that mental illnesses such as schizophrenia, bipolar disorder and major depression are more common among those born in the spring -- so this finding in anorexia is perhaps not surprising. . . .researchers believe that environmental factors around the time of conception or when the baby is developing in the womb may be responsible. . . . Seasonal changes in temperature, sunlight exposure and vitamin D levels, maternal nutrition and exposure to infections are all possible risk factors. Identifying these risk factors is important in helping us understand and maybe even prevent illness in future.
Meanwhile:
An examination of the birth records of the more than 7 million children born in the state of California during the 1990s and early 2000s has found a clear link between the month in which a child is conceived and the risk of that child later receiving a diagnosis of autism." The risk of having a child with an autism spectrum disorder grew progressively throughout the fall and winter to early spring, with children conceived in March having a 16 percent greater risk of later autism diagnoses, when compared with July conceptions.
The researchers said the finding suggests that environmental factors, for example, exposure to seasonal viruses like influenza, might play a role in the greater risk they found of children conceived during the winter having autism.
"The study finding was pronounced even after adjusting for factors such as maternal education, race /ethnicity, and the child's year of conception." . . . Each month was compared with July, with an 8 percent higher incidence in December, increasing to 16 percent higher in March.
The study lacked the means to discern if conception or some later point in pregnancy was the source of the vulnerability.
Monday, August 1, 2011
Galileon Symmetries
A scalar field in a multidimensional space is simply a function that can be described with a single number at each point in that space. For example, in classical physics, temperature is a scalar field, since each coordinate in time and space can be assigned a single number that corresponds to its temperature, which can be expressed as a single number.
One way of looking at General Relativity (one of whose core principles is independence of any fixed coordinate system), is to see it as a scalar field in five dimensional space (you could think of the fifth dimension in General Relativity as a point's "relativistic character") rather than as a tensor field in four dimensional place, as it is conventionally described. Analysis of the symmetries of this five dimensional scalar field representation of General Relativity suggested the idea of a new kind of symmetry that can exist in any kind of scalar field called a Galilean symmetry. As the Cosmic Variance blog explains:
In other words, if you take the principle of coordinate system independence, and bound by that assumption project a mathematically equivalent version of a complicated theory like general relativity into more dimensions, you can end up with simpler equations that have to fit a very constrained form.
By analogy, the point, line, circle, ellipse, parabola, and hyperbola in two dimensions can all be described as slices of a pair of cones that meet at the tip and share a common axis (i.e. as conic sections), that can be described by a very narrow set of polynomial equations with a small number of generalizable properties.
Any time that we know that a law of physics must follow Galileon symmetries, we can hope to considerably narrow the range of equations that could possibly describe it from the universe of equations that would be eligible if we didn't know that this constraint existed. And, we can also better focus the efforts of our mathematical theorists if they only have to figure out how to solve equations that can only have one or more of five very specific kinds of terms, than we could if we had to solve more general versions of the same equations.
Knowing the limited kinds of terms that Galileon scalar field equations can take also makes it very easy to immediately determine that an equation proposed to describe a scalar field with a Galileon symmetry is incorrect because it has the wrong kind of term in it without doing any other analysis of what those equations imply for the real world.
Since one of the main problems in developing the math necessary for a quantum theory of gravity is that it is non-renormalizable, but you can create a Galileon set of equations for general relativity for which in inability to renormalize is not a problem, this mathematical trick has the potential to be a big deal for quantum gravity theorists.
This is particularly useful in considering the idea that gravitons have mass, or alternately that the energy of gravitational fields themselves contribute to the mass-energy tensor, and what that implies in terms of modifications of gravitational theories that could have an impact on our understanding of dark matter and dark energy.
A 2011 paper, illustrates this concept in a context easier to grasp than the cosmological inflation example cited at Cosmic Variance is that it helps explain how dark energy could function in very weak gravitational fields (such as those found in deep space between galaxies) but not in strong ones such as the gravitational field we observe in the solar system.
Spelling note: The term Galileon is derived from the name of the scientist Galieo. I have seen both "Galileon" and "Galilean" used in print for this term, for example, even in the same post at Cosmic Variance. I have perferred the former, given its origins, and have imposed consistency of spelling on this post. It may be that different spellings are used in different senses of the word and that I have not read carefully enough to discern them.
One way of looking at General Relativity (one of whose core principles is independence of any fixed coordinate system), is to see it as a scalar field in five dimensional space (you could think of the fifth dimension in General Relativity as a point's "relativistic character") rather than as a tensor field in four dimensional place, as it is conventionally described. Analysis of the symmetries of this five dimensional scalar field representation of General Relativity suggested the idea of a new kind of symmetry that can exist in any kind of scalar field called a Galilean symmetry. As the Cosmic Variance blog explains:
[A scalar field that obeys the Galilieon symmetry is a] scalar field theory with a single complicated derivative interaction, obeying the galileon symmetry under which the action is invariant when derivatives of the field are shifted by a constant vector. . . .
[T]he realization that there existed a previously unconsidered symmetry of scalar field theories led Nicolis, Rattazzi and Trincherini to consider abstracting the symmetry, and asking what other terms may be allowed for scalar fields. And, remarkably, there turn out to only be five! In this abstracted scalar field theory we refer to these terms as the galileon terms, and to the scalar field itself as the Galileon.
[T]here are a number of properties they have that should illustrate why a number of people in the community have found them sufficiently interesting to warrant further study.
1. The Galileon terms involve higher derivatives, but their equations of motion are only second order in time, and hence they avoid some well-known proofs of instability that plague a lot of higher derivative systems.
2. There exists a range of energy scales over which the Galileon terms are important, and hence higher derivatives are important, yet quantum mechanical effects are irrelevant, and classical physics holds.
3. The Galileon terms are unrenormalized! Their coefficients pick up no modifications from quantum corrections arising from other Galileon terms!
This last feature hints at a number of possible applications in cosmology. For example, cosmic acceleration, either in the early or the late universe, typically requires scalar fields with dynamics that are finely tuned, and hence are easily perturbed by quantum corrections. There is therefore the possibility that Galileons may lead to a natural way to achieve such behavior.
In other words, if you take the principle of coordinate system independence, and bound by that assumption project a mathematically equivalent version of a complicated theory like general relativity into more dimensions, you can end up with simpler equations that have to fit a very constrained form.
By analogy, the point, line, circle, ellipse, parabola, and hyperbola in two dimensions can all be described as slices of a pair of cones that meet at the tip and share a common axis (i.e. as conic sections), that can be described by a very narrow set of polynomial equations with a small number of generalizable properties.
Any time that we know that a law of physics must follow Galileon symmetries, we can hope to considerably narrow the range of equations that could possibly describe it from the universe of equations that would be eligible if we didn't know that this constraint existed. And, we can also better focus the efforts of our mathematical theorists if they only have to figure out how to solve equations that can only have one or more of five very specific kinds of terms, than we could if we had to solve more general versions of the same equations.
Knowing the limited kinds of terms that Galileon scalar field equations can take also makes it very easy to immediately determine that an equation proposed to describe a scalar field with a Galileon symmetry is incorrect because it has the wrong kind of term in it without doing any other analysis of what those equations imply for the real world.
Since one of the main problems in developing the math necessary for a quantum theory of gravity is that it is non-renormalizable, but you can create a Galileon set of equations for general relativity for which in inability to renormalize is not a problem, this mathematical trick has the potential to be a big deal for quantum gravity theorists.
This is particularly useful in considering the idea that gravitons have mass, or alternately that the energy of gravitational fields themselves contribute to the mass-energy tensor, and what that implies in terms of modifications of gravitational theories that could have an impact on our understanding of dark matter and dark energy.
A 2011 paper, illustrates this concept in a context easier to grasp than the cosmological inflation example cited at Cosmic Variance is that it helps explain how dark energy could function in very weak gravitational fields (such as those found in deep space between galaxies) but not in strong ones such as the gravitational field we observe in the solar system.
Spelling note: The term Galileon is derived from the name of the scientist Galieo. I have seen both "Galileon" and "Galilean" used in print for this term, for example, even in the same post at Cosmic Variance. I have perferred the former, given its origins, and have imposed consistency of spelling on this post. It may be that different spellings are used in different senses of the word and that I have not read carefully enough to discern them.
Easter Islanders Were Sophisticated Gardeners
The Austronesian transoceanic colonists who settled Easter Island are famous for being excellent open water navigators and sailors who were capable of making monumental rock figurines that mystify us today.
It now appears that they also employed advanced agricultural methods designed to combat dry soil and winds and infertile soils, by shielding gardens from the wind, creating air turbulence in gardens with broken rocks, and extracting (knowingly or unknowingly) plant nutritional minerals from broken rocks placed in gardens. Absent these innovations, their civilization surely would have collapsed much sooner.
It now appears that they also employed advanced agricultural methods designed to combat dry soil and winds and infertile soils, by shielding gardens from the wind, creating air turbulence in gardens with broken rocks, and extracting (knowingly or unknowingly) plant nutritional minerals from broken rocks placed in gardens. Absent these innovations, their civilization surely would have collapsed much sooner.
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