More Conjectures On Physics

* I suspect that ultimately the speed of light is an average value, but at the ultimate quantum level, only an average value, and that deviations of the speed of light above or below the speed of light does not give rise to the phenomena associated with a tachyon in standard General Relativity, because the variation in the speed of light arises due to the space-time medium being slightly inhomogeneous at subatomic distance scales and hence to slight local variations in the true speed of light, rather than to true propagation of a particle in excess of the speed of light. I suspect this mostly due to the form of the path integral in the photon propagator in quantum electrodynamics which requires consideration of such paths and from the notion in loop quantum gravity that the dimensional and local nature of space-time is emergent, rather than a fundamental assumption of the theory.

* I suspect that space-time is ultimately local and real, but is not causal. In other words, I suspect that a real particle actually takes some particular path from point A to point B, but that sometimes events in the future influence events in the past, rather than visa versa. I suspect this mostly because quantum entanglement effects between two non-local effects always take place within the same light-cone connected at the point of entanglement. This suspicion also comes from the guess that deja vous is sometimes a result of genuine premonitions and not merely psychological hallucination.

* I suspect that H. Nikolic's construction of an energy-momentum tensor for the gravitational field in General Relativity (something that is commonly claimed not to exist), by using second as well as first derivatives to construct it, is correct, and is critically important to development of quantum gravity. This also means that total energy-momentum conservation does not need to be defined using a pseudo-tensor as a substitute.

* I suspect that dark matter phenomena are mostly a function of graviton self-interaction (as described in the previous post at this blog), of a cutoff in graviton wavelength that is a function of the size of the universe (something suggested by Lubos Motl in a post considering MOND theory), or of non-luminous ordinary matter emitted on the axis of the central black holes of galaxies and other kinds of non-luminous ordinary matter found in abundance only in galactic clusters (or some combination of the these sources), and that there is not, in fact, a non-Standard Model dark matter particle. But, this is not a strong expectation. If also believe that there is a reasonable probability that there would be a singlet massive dark matter fermion in the gravitational sector (perhaps a spin-1/2 sterile neutrino or a spin-3/2 gravitino), and that if there is one that it probably has a mass on the order of a 2 keV.

* I suspect that the Standard Model particle set, apart from a graviton (and possibly a singlet dark matter fermion, is complete) and that no new fundamental particles or forces (with the exceptions of a possible graviton and a light singlet dark matter fermion) will be discovered.

* I suspect that Mach's principle (i.e. the collective gravitational pull of all other mass-energy in the universe on each particle of mass-energy) explains inertia, rather than the Higgs field, which imparts mass to the Standard Model fermions, but is not the source of mass for the vast majority of the rest mass of the proton and the neutron which makes up the bulk of the rest mass in the universe that is not attributable to dark matter. Thus, inertia mass and gravitational mass are identical because inertia arises from gravity. Note that inertia, via the formula F=ma impacts the second derivative of position (i.e. acceleration), rather than the first derivative of position (i.e. velocity). So, that bosons with zero rest mass maintain a constant velocity (equal to c, the speed of light), does not contradict this formula so long as additional force impacts relativistic mass-energy, rather than speed.

* I suspect that neutrinos have Dirac mass arising from interactions with the weak force bosons (W+, W- and Z bosons) and the Higgs boson, rather than Majorana mass. I suspect this mostly because the non-identity of neutrinos and anti-neutrinos was the primary reason that they were hypothesized to exist in the first place, and because none of the Standard Model forces would interact with right handed neutrinos. Likewise, most right handed neutrino theories call for right handed neutrinos to have different masses than left handed neutrinos contrary to all other right handed version of Standard Model particles which have the same mass regardless of whether they are left handed, right handed, and regardless of their matter or anti-matter character.

* I suspect that the neutrino masses have a normal hierarchy, and that the mass of the electron neutrino is on the order of 1 meV or less.

* I suspect that there is a great deal of CP violation in the PMNS matrix.

* I suspect that no light sterile neutrinos of a mass necessary to explain the reactor anomaly exists, and that any difference between the measured value of the effective number of cosmological neutrinos, Neff and the theoretically predicted value with the three Standard Model neutrinos of 3.05 is due to experimental measurement error. A sufficiently heavy sterile reactor neutrino with a mass ca. 1 eV would not be inconsistent with cosmological measures of Neff, but would contradict cosmological measurements of the maximum sum of the combined neutrino mass states. The latest reactor measurements also tend to disfavor a four flavor oscillation model.

* I suspect that the anomaly in the radius of muonic hydrogen is due to experimental measurement error in the measurement of ordinary hydrogen, and conceptual theory errors in comparing the two.  Similarly, I suspect that the anomalous magnetic moment of the muon relative to the theoretically predicted value in QED is due to an underestimate of systemic error in the relevant measurements.

* I suspect that two times the rest mass of the Higgs boson is exactly equal to twice the W boson rest mass plus the Z boson rest mass, subject only to a possible definitional adjustment for μ, the energy scale at which these masses are determined (this is a natural corollary to the fact that: "In the Standard Model, the Higgs field consists of four components, two neutral ones and two charged component fields. Both of the charged components and one of the neutral fields are Goldstone bosons, which act as the longitudinal third-polarization components of the massive W+, W–, and Z bosons. The quantum of the remaining neutral component corresponds to (and is theoretically realised as) the massive Higgs boson." The W and Z bosons are intimately related to the Higgs boson in the electroweak interaction, for example, with mass squared terms of these particles with the right signs and coefficients as the proposed simple relationship appearing in the kinetic term of the electroweak Lagrangian.

* I also suspect that the Higgs boson mass is a mass that implies a vacuum that is metastable, or a vacuum that is precisely on the bound between vacuum stability and vaccuum metability once quantum gravity effects are considered (see also here), and that it is a mass that maximizes photon decays. It also very nearly minimizes the second loop terms in the MS mass to pole mass conversion.  It is not, however, a mass that causes the square of the masses of the Standard Model fermions to be exactly equal to the masses of the Standard Model bosons, although these are quite close to each other and might be equal as some energy scale given the running of the Standard Model particle masses.

* I suspect that the Higgs boson has exactly the properties predicted in the Standard Model for a Higgs boson mass of the magnitude measured, and that there are no additional Higgs bosons. This conclusion is strongly supported by experimental data to date.

* I suspect that the sum of the square of the rest masses of the fundamental particles is precisely equal to square of the Higgs vacuum expectation value, for a properly defined set of rest masses of these particles. Put another way, the sum of the Yukawa couplings to the Higgs field (or the equivalent in the case of the Higgs boson and weak force bosons) is unitary (i.e. exactly equal to 1.00).

* I suspect that all deviations between the Standard Model and actual physics at energy scales approaching the Planck scale are due to corrections for quantum gravity effects.

* I suspect that the discrepancy between the strength of the scalar dark energy field implied by the cosmological constant, and the strength of the Higgs vacuum expectation value, may arise because the Higgs vev is best understood as a short range field emitted by massive Standard Model fundamental particles that is absent in truly empty space, rather than as a scalar field that actually permeates the entire vacuum as a background field with which Standard Model fundamental particles interact.

* I suspect that a simultaneous solution for all six quarks of a generalization of Koide's rule that takes into account all of the quarks into which a quark can transform in an appropriate manner explains the relative masses of the six Standard Model quarks, and that Koide's rule is exact for the charged leptons subject only to deviations arising from the differences in the interactions of charged leptons with flavor oscillating neutrinos in W boson interactions with charged leptons. I also suspect that the relative neutrino masses fit a generalization of Koide's rule. I suspect that these Koide's rule relationships between the relative masses of the fundamental particles in the Standard Model arise dynamically from the weak force W boson interactions of quarks and leptons, with the Koide's ratio of 2/3rd representing a division of mass between a source particle, an intermediate particle, and its decay product, in the simple case, that is equidistant between a degenerate state of three equal masses and a maximally unequal state with two zero masses and one non-zero mass.

* I suspect that the difference between the masses of the neutrinos and the masses of the charged leptons is at some fundamental level tied to the relative strengths of the electromagnetic force which acts on all charged particles but not on the neutrinos, and the weak force, which acts on all massive Standard Model fundamental particles. The average ratio of charged lepton mass and neutrino mass might be equal to the ratio of the weak force coupling strength to the electromagnetic coupling strength, and a Koide's rule-like relationship might explain the relative masses of the three mass states. For example, the weak force is on the order of 10¹¹ times weak than the electromagnetic force, while by comparison, the mass of the tau leptons is roughly 3.5*10¹⁰ times the mass of the heaviest neutrino mass eigenstate in a normal hierarchy with a lighest neutrino mass eigenstate of less than 1 meV. And, with those assumptions the mass of the muon is roughly 1.3*10⁹ times the middle neutrino mass eigenstate. Perhaps, for example, only charged massive fermions interact directly with the Higgs field (as in the original Standard Model with massless neutrinos), and neutrinos acquire their masses indirectly, via W and Z boson interactions between charged leptons that acquire mass directly from the Higgs field, and neutrinos, that is roughly proportionate to the strength of these interactions. These interactions via the weak force might fulfill a role similar to hypothetical see-saw interactions between hypothetical right handed neutrinos and the Standard Model neutrinos. The slightly smaller ratio of interaction might flow from the fact that there are three separate weak fields (W+, Z and W-) interacting between the particles that add together to generate the neutrino masses. An alternative analysis arising from the same general observation considers the possibility that particle masses arise from self-interactions of particles with themselves.

* I suspect that QCD has no CP violation in the high energy perturbative QCD regime because gluons have zero rest mass and a massless force carrying boson does not experience time in general relativity (the same is true of photons and gravitons). But, since gluons appear to dynamically acquire mass in the low energy infrared regime when confined in hadrons, there might be CP violation in the low energy non-perturbative regime of QCD.

* I would not be surprised if the CP violation that the Standard Model explains as a CP violating phase of the CKM matrix (and probably the PMNS matrix as well) is actually an analytically distinct phenomena from the CKM matrix, and were related to each other.  But, the small magnitude of CP violation effects in most CKM matrix elements relative to the magnitude of the non-CP violating effects, masks those effects in most contexts.

* I would not be surprised if the CKM matrix (apart from the CP violating phase) can be accurately parameterized with a single experimentally determined parameter, λ, with the value given to it in the Wolfenstein parameterization.

* I suspect that following the Big Bang at t=0+ε, that the universe was matter dominated and that this is balanced by an anti-matter universe on the other side of the Big Bang in which time seems to move in the opposite direction that is anti-matter dominated. Thus, I suspect that no baryon number violating or lepton number violating process sufficient to explain the baryon asymmetry of the universe will be discovered. In particular, this implies that neither proton decay, nor neutrinoless double beta decay, will ever be observed.

* I suspect that lepton flavor violation is as rare as it is predicted to be in the Standard Model in charged leptons (see also here and here), which arises only when induced by neutrino flavor oscillation. Note also that the GIM mechanism suppresses flavor changing neutral currents and charged lepton flavor violation in the Standard Model. A lack of charged lepton flavor violation largely follows from a conclusion that neutrinos have Dirac mass.

* I suspect that indications of violations of lepton universality will turn out to be statistical flukes or due to systemic errors.

* Juan Ramón González Álvarez argues that a field theory with a spin-2 graviton (presumably operating in the Minkowski space-time of special relativity) is not quite equivalent to the purely geometrical approach of classical General Relativity, but the differences between the two are quite subtle. These inconsistencies have long been a formidable barrier to unifying the Standard Model and General Relativity, in an analysis also driven in part by dissatisfaction with the energy-matter conservation pseudo-tensor of General Relativity. I wouldn't be at all surprised if reality actually involves a spin-2 graviton acting in a flat Minkowski space-time, rather than the curved space-time of General Relativity, in part because at the level of cosmology, space-time is remarkably flat.

* I suspect that there are only four space-time dimensions, although this may be an emergent property of space-time.  Put another way, I suspect that models with Standard Model interactions limited to a four dimensional brane, while gravity operates in more dimensions, or a model with compactified extra dimensions (such as a Kaluza-Klein model), is not an accurate description of reality.

* I would not be surprised if the Standard Model force coupling constants converge due to slight tweaks in their beta functions at high energies that arise from subtle theoretical considerations or due to quantum gravity effects (e.g. asymptotic safety considerations). Weinberg had thought that there would be a unification of coupling constants in the Standard Model back in 1981, but subsequent data suggested otherwise.

For example, the QCD coupling constant beta function is, in part, a function of the effective number of quark flavors in the model. And, while usually, only five quark flavors of QCD hadronize, since the top quark has a lifetime about 1/10th of the typical hadronization time in QCD, theoretically, a small percentage of top quarks should live long enough to hadronize for a brief moment. This, in turn, might cause the number of effective hadronizing flavors in QCD in the real world to be 5.1 rather than 5, which might slightly impact the beta function of the QCD coupling constant α_s at energies in excess of twice of the top quark mass (ca. 346 GeV). Current experimental measurements are not precise enough to distinguish a distinction between the beta function of 5 flavor QCD and 5.1 flavor QCD (the strong force coupling constant itself is known to a precision of roughly 0.6% in the weighted average although individual measurements vary by up to 3% or more from each other). Yet, a tweak of this magnitude could easily cause the strong force coupling constant to get 78% rather than 75% weaker between 1 TeV and a bit more than 10¹² GeV as it would need to for there to be a gauge coupling constant unification at 10¹² GeV where the electromagnetic coupling constant and weak force coupling constant converge in the Standard Model. A tweak of this nature, incidentally, would also make SUSY models, in which the three gauge coupling constants always do converge, less attractive because this feature would be replicated in the Standard Model.

Footnote: There is a nice power point summary of flavor physics in the Standard Model here.

Is Dark Matter Just The Self-Interaction Of Gravitons?

We discuss the correlation between the dark matter content of elliptical galaxies and their ellipticities. We then explore a mechanism for which the correlation would emerge naturally. Such mechanism leads to identifying the dark matter particles to gravitons. A similar mechanism is known in Quantum Chromodynamics (QCD) and is essential to our understanding of the mass and structure of baryonic matter.

Alexandre Deur, "A correlation between the amount of dark matter in elliptical galaxies and their shape" (28 Jul 2014).

Every now and then there is a paper that suggests that the phenomena described as dark matter is really implied by General Relativity, or a trivial variant of General Relativity, and that the discrepancy between theory and observation that astronomers observe is because they inappropriately conclude that in systems like galaxies and galactic clusters that Newtonian gravity is a reasonably accurate approximation of General Relativity.

This is one of the stronger arguments that I have seen for that position.

Most of those papers argue basically that what a Newtonian gravitational approximation (mediated through a stylized approximation of a galaxy's structure or a numerical many body simulation much like those of lattice QCD) is missing is the gravitational effects of the coherent angular momentum of the many bodies in a galaxy as they rotate around a central black hole.  On balance, I've found that the argument that this contribution is tiny is stronger than the argument that this is the main source of dark matter phenomena.

Put another way, they focus on the additional degrees of freedom (i.e. additional amount of information necessary to describe) the behavior of General Relativity (which requires a spin-2 tensor field graviton), rather than the spin-0 scalar field gravitons of Newtonian gravity.

This paper focuses on a different distinction between Newtonian gravitons and General Relativistic ones.  Newtonian gravitons, like real world photons, don't interact with each other.  They couple only to mass and electric charge, respectively.  In contrast, in General Relativity, gravity is a function of both mass and energy.  Thus, gravity can influence particles that have zero rest mass (i.e. photons and gluons), and in principle, gravity may even influence other gravitons.  In this respect gravitons are more like gluons, which interact both with quarks and with each other, and less like photons.

Focusing on this self-interaction of gravitons suggests an effect of approximately the right order of magnitude to account for differences in the amount of "dark matter" effects seen in ellipical galaxies of different sizes.  A previous paper from 2009 argues that the effect is on the right order of magnitude to account for the rotation curves of galaxies and the Tully-Fisher relation, and may also explain, or at least help to explain, dark matter phenomena in galaxy clusters.

I haven't had the time to rigorously review the accuracy of the analysis, but the approach does look like a fruitful one to explore that is understudied. Deur basically claims to have derived a versions of MOND (Milgrom's modified gravity theory) from first principles using a toy model approximation of GR that preserves the essentials of General Relativity in a symmetric and homogeneous case, while proving much more accurate for galactic clusters and that can explain the Bullet Cluster.

An interesting analysis of what would distinguish MOND from MOND-like theories is found in another 2009 paper by another author.

If he's right, he deserves the Nobel prize for physics. If this approach really works, of course, it would also eliminate the phenomenological need for any beyond the Standard Model particles other than the graviton, which is by far the best empirically supported hypothetical particle. Given our failure to discovery any other dark matter candidates, this increasingly looks like a feature rather than a bug.

Deur's approach was also discussed recently at the Physics Forums.

Bubonic Plague In China

Summary

Modern genetic techniques and assimilation of global historical accounts have revealed that the Black Plague that devastated Europe in the Middle Ages, originated in Asia and arrived via the Silk Road trade route.  To recap some key dates (all in the current era):

* Yuan Empire, China 1331
* Hebei Province, China 1334 (the province that surround the Beijing province in northern coastal China)
* Persia 1335
* Kyrgyzstan 1338-1339
* Kaffa, Crimea 1344
* Syria 1345-1348
* Mecca, Saudi Arabia 1349

Kublai Khan's Yuan Empire with a capitol in Beijing, included by 1294 CE, all of modern China except the Tarim Basin, all of Mongolia and Korea, and some of the adjacent territory in what is now Russia to the North of Mongolia and Manchuria. The Yuan Dynasty extended from 1271 CE to 1368 CE, not quite a century, and not long after the plague ravaged China. (The long lived Ming Dynasty originating in Southern China followed the Yuan Dynasty).

Analysis

The role of the expanding plague and the depopulation and chaos left behind in its wake also makes the rapid expansion of the Mongolian Empire resemble much more closely than is commonly realized, the expansion of European conquest in the New World following the arrival of Columbus, and small pox, in 1492 CE. The Golden Horde may have accumulated plague immunity by the time it reached Europe.

The backdrop of the plague also helps explain the population genetic impact of the Mongol Dynasty in Asia, since it swept into a population bottleneck that subsequently expanded. And, it explains the fall of the Yuan Dynasty in China itself.

Sources

According to one not particularly reliable source, which I nonetheless have no particular reason to doubt:

Many scholars believe that the Black Death began in north-western China, while others cite south-western China or the steppes of Central Asia. We do know that in 1331, an outbreak erupted in the Yuan Empire; it may have hastened the end of Mongol rule over China. In 1334, this disease killed 5 million people in Hebei Province - about 90% of the population.  As of 1200, China had a total population of more than 120 million, but a 1393 census found only 65 million Chinese surviving. Some of that missing population was killed by famine and upheaval in the transition from Yuan to Ming rule, but many millions died of bubonic plague.

From its origin at the eastern end of the Silk Road, the Black Death rode trade routes west. At Central Asian caravanseries and Middle Eastern trade centers, it infected people all across Asia. . . .

Ibn al-Wardi, a Syrian writer who would later die of the plague himself in 1348, recorded that the Black Death came out of "The land of Darkness" (Central Asia). From there, it spread to China, India, the Caspian Sea and "land of the Uzbeks," and thence to Persia and the Mediterranean.  The Egyptian scholar Al-Mazriqi noted that "more than three hundred tribes all perished without apparent reason in their summer and winter encampments, in the course of pasturing their flocks and during their seasonal migration." He claimed that all of Asia was depopulated, as far as the Korean Peninsula. (Orent, 106)

The Central Asian scourge struck Persia just a few years after it appeared in China - proof, if any is needed, that the Silk Road was a convenient route of transmission for the deadly bacterium.  In 1335, the Il-Khan (Mongol) ruler of Persia and the Middle East, Abu Said, died of bubonic plague during a war with his northern cousins, the Golden Horde. This signaled the beginning of the end for Mongol rule in the region.  An estimated 30% of Persia's people died of the plague in the mid-14th century. The region's population was slow to recover, in part due to the political disruptions caused by the fall of Mongol rule and the later invasions of Timur (Tamerlane).

Archaeological excavations on the shores of Issyk Kul, a lake in what is now Kyrgyzstan, reveal that the Nestorian Christian trading community there was ravaged by bubonic plague in 1338-39. Issyk Kul was a major Silk Road depot, and has sometimes been cited as the origin point for the Black Death. It certainly is prime habitat for marmots, which are known to carry a virulent form of the plague.  It seems more likely, however, that traders from further east brought diseased fleas with them to the shores of Issyk Kul. Whatever the case, this tiny settlement's death rate shot up from a 150-year average of about 4 people per year, to more than 100 dead in 1338-39. 

Although specific numbers and anecdotes are hard to come by, different chronicles note that Central Asian cities like Talas, in modern-day Kyrgyzstan; Sarai, the capital of the Golden Horde in Russia; and Samarkand, now in Uzbekistan, all suffered outbreaks of the Black Death. It is likely that each population center would have lost at least 40% of its citizens, with some areas reaching death tolls as high as 70%. 

In 1344, the Golden Horde decided to recapture the Crimean port city of Kaffa from the Genoese, Italian traders who had taken the town in the late 1200s. The Mongols under Jani Beg instituted a siege, which lasted until 1347, when reinforcements from further east brought the plague to the Mongol lines.

An Italian lawyer, Gabriele de Mussis, recorded what happened next: "The whole army was affected by a disease which overran the Tartars [Mongols] and killed thousands upon thousands every day." He goes on to charge that the Mongol leader "ordered corpses to be placed in catapults and lobbed into the city in hopes that the intolerable stench would kill everyone inside."

This incident is often cited as the first instance of biological warfare in history. However, other contemporary chroniclers make no mention of the putative Black Death catapults. A French churchman, Gilles li Muisis, notes that a "calamitous disease befell the Tartar army, and the mortality was so great and widespread that scarcely one in twenty of them remained alive." However, he depicts the Mongol survivors as surprised when the Christians in Kaffa also came down with the disease.

Regardless of how it played out in fact, the Golden Horde's siege of Kaffa certainly did drive refugees to flee on ships, bound for Genoa. These refugees likely were a primary source of the Black Death that went on to decimate Europe.

European observers were fascinated but not too worried when the Black Death struck the western rim of Central Asia and the Middle East. One recorded that "India was depopulated; Tartary, Mesopotamia, Syria, Armenia were covered with dead bodies; the Kurds fled in vain to the mountains." However, they would soon become participants rather than observers in the world's worst pandemic.

In "The Travels of Ibn Battuta," the great traveler noted that as of 1345, "the number that died daily in Damascus [Syria] had been two thousand," but the people were able to defeat the plague through prayer. In 1349, the holy city of Mecca was hit by the plague, likely brought in by infected pilgrims on the hajj.

The Moroccan historian Ibn Khaldun, whose parents died of the plague, wrote about the outbreak this way: 

Civilization both in the East and the West was visited by a destructive plague which devastated nations and caused populations to vanish. It swallowed up many of the good things of civilization and wiped them out... Civilization decreased with the decrease of mankind. Cities and buildings were laid waste, roads and way signs were obliterated, settlements and mansions became empty, dynasties and tribes grew weak. The entire inhabited world changed.

This source cites, as its sources:

* Benedictow, Ole Jorgen. The Black Death, 1346-1353: The Complete History (2004).
* Marshall, Robert. Storm from the East: From Ghengis Khan to Khubilai Khan (1993).
* McNeill, William Hardy. Plagues and People (1976).
* Orent, Wendy. Plague: The Mysterious Past and Terrifying Future of the World's Most Dangerous Disease (2004).

Wikipedia cites:

* As evidence of the genetic origin of the plague in China, Nicholas Wade (31 October 2010). "Europe’s Plagues Came From China, Study Finds". The New York Times. Retrieved 1 November 2010. This report was actually based upon: G. Morelli et al. (2010) Nature Genetics. December; 42 (12):1140-1143. doi:10.1038/ng.705.

* Regarding the Lake Issyk Kul outbreak in Kyrgizstan, Raoult; Drancourt (2008). Paleomicrobiology: Past Human Infections. Springer. p. 152.

* The Cambridge History of China: Alien regimes and border states, 907–1368, p.585 for the proposition ("In the 1330s a large number of natural disasters and plagues led to widespread famine, starting in 1331, with a deadly plague arriving soon after."), and

* Kohn, George C. (2008). Encyclopedia of plague and pestilence: from ancient times to the present. Infobase Publishing. p. 31. ISBN 0-8160-6935-2, as evidence of an early Chinese outbreak ("The 14th-century plague killed an estimated 25 million Chinese and other Asians during the 15 years before it reached Constantinople in 1347.", i.e. from 1332-1347 CE).

* But, Wikipedia notes the lack of a clear medical description of the bubonic plague in China until 1644, relying on Sussman GD (2011). "Was the black death in India and China?". Bulletin of the history of medicine 85 (3): 319–55. doi:10.1353/bhm.2011.0054. PMID 22080795.

There is another Wikipedia article here that specifically addresses the migration of the Black Plague.  It cites regarding the Chinese Outbreak:

* McNeill, William H. (1976). Plagues and People. New York: Anchor Books. ISBN 0-385-12122-9.

How Big Are The Solid Planets? A Handy Illustration

This excludes Neptune, Saturn and Jupiter, which lack solid surfaces, but includes Moons and minor planets.  It is remarkable how much of the solid surface of our solar system is on Earth.  Other bodies in the solar system are surprisingly small.

This also illustrates some of the limits to accommodating an expanding human population by settling space.  Very thinly inhabited parts of the surface of Earth like the Sahara desert, Antarctica, the Australian Outback, Siberia, and the surfaces of the oceans are much more attractive places to live than anyplace that is not on Earth.

Discrepancies in CKM Matrix Measurements Not Due To New Physics

Two different ways of measuring two of the nine CKM matrix elements (the charm quark to bottom quark and the up quark to bottom quark elements; both of which are tiny relative to the top quark to bottom quark element in this unitary matrix) have produced inconsistent results at a 3sigma plus level.

But, a careful analysis of the kind of new physics that would be necessary to replicate this behavior shows that there is only one theoretically consistent way of achieving the experimentally observed data.  The only approach that can fit this data, however, has other implications that much more accurate measurements rule out.  Therefore, the analysis appropriately concludes that the apparent discrepancy in the two different ways of measuring these CKM matrix elements is due to underestimated systemic errors (by 50% or more), rather than new physics.

Reconciling GR and QCD

An ambitious new paper demonstrates in a brief ten pages how to generalize lattice quantum chromodynamics (QCD) (an approach to calculating strong force interactions using the actual equations of the Standard Model in a discrete approximation that is not scale dependent) to incorporate curved space-times, such as the classical version of general relativity.

Reconciling the Standard Model to General Relativity is a Holy Grail of fundamental physics.  And, even if one can't accomplish this result for both electro-weak interactions and strong force interaction, doing so with the strong force part of the Standard Model is an impressive accomplishment.

The ordinary assumption is that GR and the Standard Model can be reconciled only by formulating a new theory of quantum gravity.  But, in the case of lattice QCD models, the authors show that QCD and GR can be reconciled using ordinary classical general relativity's equations.

As a corollary of this new approach, the authors demonstrate analytically (rather than merely by numerical approximation) for all curved space-times, that QCD does not permit free gluons even in the intense gravitational fields of neutron stars and black holes, contrary to numerous previous speculations that deconfinement (i.e. the existence of particles that are not part of a color charge neutral composite particle) might occur in those circumstances. 

This paper also paves the way for determining definitively using numerical approximations, if free quarks can exist in strong gravitational fields, and confirms that a quirk of lattice QCD calculations called the double fermion problem is also present in curved space-times.  But, the authors reserve resolution of this issue for further resolution.

Still No Sign of CPT Symmetry Violations

Overview

There is no experimental evidence for CPT symmetry violations to date. CPT symmetry widely believed to be a perfect symmetry, unlike CP symmetry.  New experimental data tightens the experimental boundaries on any potential CPT symmetry violations by a factor of up to 100.

Background

What is CP Symmetry Violation?

CP violation is a rare "arrow of time" in the laws of physics.  In certain neutral mesons, decays of matter and anti-matter version of the neutral mesons do not decay at the same rates, and the forward and backward versions of these decays occur at different rates.

CP symmetry is violated in a few esoteric circumstances driven in the Standard Model entirely by (1) the CP violation phase in the CKM matrix, and (2) the CP violation phase in the PMNS matrix, if any, which governs transitions between neutrino mass states.  The latest neutrino physics data favor CP violation in neutrino oscillation, but aren't yet definitive.

Experimental evidence of CP violation is restricted to electrically neutral mesons (originally, neutral kaons where it was first observed in 1964; CP violation in other mesons was not observed until 2001), even though, in principle, it is present at tiny levels too small to be detected by current experiments in all weak force interactions of quarks.

What is CPT Symmetry Violation?

CPT violation says that (1) if any physical process proceeds differently starting at one point and ending at another, from the way it would if it started at that end point and ended at that starting point (i.e. reversed in the time coordinate), then (2) the process is identical except that the charge and parity of the interaction is reversed when the direction in time of the process is reversed.

CPT symmetry violation also implies a violation of Lorentz invariance. Lorentz invariance means that the laws of special relativity is perfectly observed. Special relativity, in turn, implements to law of nature that says nothing can exceed the speed of light in a particularly elegant way. For example, special relativity modifies Newton's laws of motion because momentum does not translate linearly into acceleration, so that it takes more momentum to produce the same increment of additional velocity as one approaches the speed of light. Special relativity also provides that time slows down in accelerating objects relative to objects at rest with time standing still in the limit of the reference frame of a photon moving at the speed of light.

The New Data

New experimental data from the Large Hadron Collider (LHC) from the decays of electrically neutral B (made of a b quark and an anti-down quark, or their respective anti-particles), B_s (made of a b quark and an anti-strange quark, or their respective anti-particles) and D mesons (made of a charm quark and an anti-down quark, or their respective anti-particles) tightens already strict experimental constraints on CPT violation.

The old constraints on CPT violation are expressed in a formalism where the CPT violation parameter delta alpha sub mu is expressed in units of GeV/c² were on the order of 10^-12 to 10^-14.  A smaller parameter means a tighter constraint on any possible CPT violations.

Current experimental constraints in neutral kaons (which are made of a strange quark and an anti-up quark, or their respective anti-particles), are much more strict, with limits on the CPT violation parameter delta alpha sub mu of about 2*10^-18 and limits on a related parameter which is of the same order of magnitude in B and B_s mesons of less than 5*10^-21.

The improvement in the B and B_s meson cases is two orders of magnitude (i.e. a factor of 100), and in  the D meson case by about 1 order of magnitude (i.e. a factor of 10), to new constraints on the order of 10^-14 for D and B_s mesons and 10^-15 for B mesons without strange quarks. The conclusion to the paper states (with internal cross references omitted):

We have presented new results on CPT violation in B⁰ and B_s⁰ mixing in both the classical and SME [Standard Model Extension] approach, derived from existing BaBar, Belle and LHCb data. In both approaches there is a significant improvement over previous results. LHCb will be able to further improve these numbers in the B⁰ and B_s⁰ systems, as well as in the D0 system, with dedicated analyses. In most cases these possible LHCb measurements would improve the current best values by orders of magnitude and the corresponding precision on [CPT violation parameter delta alpha sub mu] approaching the interesting region of m²/M_Pl.

M_Pl is the Planck mass, which is about 1.2209×10¹⁹ GeV/c² the Planck mass is significant in physics because it is related to the point at which the Heisenberg uncertainty principle applies, and quantum rather than classical physics is the only regime that can meaningfully analyze phenomena.

Analysis

Very few physics seriously expect there to be CPT violations in meson decays.  But, the new experimental evidence confirms this expectation experimentally to unprecedented precision, securing a bedrock principle of fundamental physics.

Lorentz invariance violations, where they are theoretically proposed at all, are detectible only over very long distances as a result of quantum gravity theories that propose that space-time is not perfectly continuous and local.

CDM Looks Better Relative To WDM With Better Models

Earlier simulations comparing cold dark matter models (with dark matter particles that are thermal relics with masses on the order of 1-1,000 GeV), with warm dark matter models (with particles typically around 2 keV), reveal that warm dark matter models produce results much more like what we see in the real work than cold dark matter models.

But, those simulations contained important simplifications, most critically, not meaningfully including the effects of ordinary baryonic matter on the overall evolution the the large scale structure of the universe and particular galaxies.

A new paper argues that many of the problems that the older models found with CDM models relative to WDM models are fixed in more sophisticated new simulations that appropriately consider the impact of a mix of ordinary baryonic matter and dark matter, rather than simply modeling pure dark matter systems.

Meanwhile, an epic 170 paper comprehensively explores alternatives to the standard lambda CDM model of cosmology that modify gravity in the weak gravitational field regime (an idea that started with Milgrom's MOND theory but has many modern variants) rather than relying at all or at least as heavily, on a dark matter hypothesis.  Despite its length, it is only a preliminary survey and does not provide a definitive resolution of these questions.

Reanalysis of Tevatron Data Disfavors Exotic Particles Under 120 GeV In Higgs Decays

Once again, the prospects of beyond the Standard Model physics at experimentally accessible scales is looking ever more bleak.

Tevatron Measurements on Standard Model Higgs

Federico Sforza, on behalf of the CDF, D0 Collaborations(Submitted on 1 Jul 2014)

We present the study of the SM Higgs properties obtained from the combined analysis of the up-to 10 fb−1 dataset collected by the CDF and D0 experiments during the pp¯ collision at s√=1.96~TeV of Tevatron Run II. The observed local significance for the SM Higgs boson signal is of 3.0σ at mH=125 GeV/c2. 

After a brief review of analysis channels contributing the most, where the Higgs boson decays to a pair of W bosons or to a pair of b-quarks jets, the signal production cross section and its couplings to fermions and vector bosons are analyzed. Other presented results are the recent study of the spin and parity of the SM Higgs performed by the D0 collaboration, leading to 3σ level expected exclusion of the JP=0− and JP=2+ hypothesis, and the investigation of exotics final states with invisible decay products of the Higgs, excluded by the CDF collaboration for masses below 120 GeV.

From here.

The Background Context and Minor Conclusions That Reaffirm Prior Data

Reanalysis of Tevatron experiment data after it shut down and after the LHC discovered the Higgs boson has revealed three sigma evidence of the 125 GeV mass Higgs boson discovered by the LHC.

This data also shows that the Higgs boson has W boson and b quark pair decays consistent with a Standard Model Higgs boson's decays.  The b quark pair decays are actually the dominant form of Higgs boson decay but are hard to detect in high energy collisions because lots of other non-Higgs boson decays have very similar end states.  But, since b quark pair decays account for something like 57% of Higgs boson decays and are the only form of decay into quarks that we expect should be detectable with current experiments, evidence that these decays happen at about the right frequency is critical to confirming the Standard Model nature of the Higgs boson and to ruling out, for example, "lepto-phillic" models of non-Standard Model Higgs bosons.

The data rule out pseudo-scalar (at the 3.1 sigma level) and tensor boson (at the 3.2 sigma level) versions of the Higgs boson, leaving the true scalar Higgs boson total angular momentum and parity of the Standard Model Higgs boson as the sole remaining viable option at the 3 sigma level (a few holdout skeptics note that a mix of scalar and pseudo-scalar Higgs bosons is not ruled out quite as strongly, but few really think that this is what we are seeing when all other evidence points so strongly to a Higgs boson indistinguishable from the Standard Model prediction of many decades ago from electro-weak unification theory).

All of this is basically old news, however, that has been revealed in previous papers from Tevatron and the LHC previously discussed at this blog.  Just click on the Higgs boson tag if you would like to review the prior results on these points.

The Big News

The critical new development announced in this paper is that it discusses "the investigation of exotics final states with invisible decay products of the Higgs, excluded by the CDF collaboration for masses below 120 GeV." This exclusion is at the 95% confidence level (i.e. two sigma).

Ruling out the production of exotic particles with masses of less than 120 GeV in Higgs boson decays is huge!

This disproves a huge swath of beyond the Standard Model theories.

For example, many beyond the Standard Model theories attempting to provide a dark matter candidate assume the existence of sterile neutrinos that don't couple to the gauge bosons of any of the three Standard Model forces, but do couple to gravity and the Higgs boson.  This result largely rules out sterile neutrino candidates of this type with masses of less than 120 GeV.

This also extends the exclusion range of an ordinary "fertile" fourth generation neutrino from about 45 GeV to about 120 GeV.  There are very sound interpretations of the current experimental evidence to suggest that the heaviest of the three currently known neutrino mass states is lighter than 0.2 eV.  Thus, the minimum mass of a fourth generation ordinary neutrino is now about 600,000,000,000 times that of the third generation neutrino (i.e. 6*10^11 times as heavy).

More generally, this rules out pretty much all plausible forms of "Higgs portal" dark matter, which has been a leading way to integrate dark matter candidates into the Standard Model framework in a minimalist manner.

Impact On SUSY Exclusions

Increasingly overwhelming experimental evidence, including this latest data point, strongly disfavor the existence of non-Standard Model SUSY particles at the electroweak scale, which was the "natural" mass range at which many original proponents of SUSY theories expected to discover these new particles.

Many still popular theories in the parameter space of supersymmetry (SUSY) theories call for "invisible" SUSY particles with masses of under 120 GeV.  This new Tevatron data regarding Higgs boson decay products therefore, impacts many theories that might otherwise be considered viable.  For example, Lubos Motl recently discussed a SUSY scenario with at least two invisible sparticles of less than 120 GeV as an attractive model.

Also, one of the main reasons to devise SUSY theories in the first place was to address the "hierarchy problem" of the seeming unnaturalness of the many contributions to the Higgs boson mass almost completely cancelling out, through mathematically obvious additional couplings to the Higgs boson that transparently cancel each other out.  So, it doesn't work to devise a SUSY theory in which sparticles don't couple to a Higgs boson and can thus escape the impact of the decay product exclusions of the new Tevatron data analysis.

The ATLAS experiment at the LHC has already set higher mass exclusions on SUSY particles, but in more model dependent ways that may not capture as many kinds of Higgs boson decay paths as the Tevatron data:

In R-parity-violating simplified models with decays of the lightest supersymmetric particle to electrons and muons, limits of 1350 GeV and 750 GeV are placed on gluino and chargino masses, respectively. In R-parity-conserving simplified models with heavy neutralinos decaying to a massless lightest supersymmetric particle, heavy neutralino masses up to 620 GeV are excluded. Limits are also placed on other supersymmetric scenarios.

Meanwhile, CMS experiment at the LHC has ruled out a large range of possible masses for heavy, Standard Model-like Higgs bosons of the type predicted in almost all SUSY theories:

A SM-like Higgs boson is excluded in the mass range 248-930 GeV at 95% CL using the shape-based analysis. . . . For the less sensitive cut-and-count analysis we obtain an observed exclusion of 268-756 GeV[.]

Other constraints, for example from the anomalous magnetic moment of the muon and the total absence of strong SUSY signals in any of the great numbers of channels studies, are discussed here, and notes that exclusions are particularly strong for sparticles of less than 300 GeV. Similarly, there is no evidence of SUSY predicted deviations from the Standard Model running of any of the three gauge coupling constants.

Matt Strassler's recent paper also identified a broad and quite comprehensive exclusion range for SUSY particle masses in "natural SUSY" models.

Direct dark matter detection experiments have also ruled out WIMP dark matter in the mass range from about 5 GeV to 1000 GeV, the bulk of the low end of the SUSY parameter space for light sparticles.

The fact that searches from multiple methodologies all confirm the absence of SUSY particles at these mass scales provides further confidence that this result is a robust one.

Exclusions of beyond the Standard Model SUSY particles at single digit TeV scales and higher masses aren't nearly so strong.  But, constraints like the expected amount of neutrinoless beta decay in many of those models, and the absence of dark matter models that can fit such heavy lightest supersymmetric particles, as well as their overall minimal impact of experimentally accessible phenomenology from the Standard Model (some of which SUSY theories were motivated to address), all make these versions of SUSY far less interesting and far less well motivated theoretically.

UPDATE July 3, 2014:

ATLAS has released four pre-prints with new, more demanding SUSY exclusion papers last night.  Needless to say, no hint of any SUSY particle was detected in any of the scenarios investigated.  Gluinos with masses of less than a bit more than 1 TeV and stop squarks with masses in the low hundreds of GeVs are excluded.

SM and SUSY Particles Reviewed

There are 18 particles in the Standard Model (ignoring color charge variants, antimatter variants of fermions and parity variants of charged fermions):
* one scalar spin-0 fundamental particle in the Standard Model (the Higgs boson) that is electrically neutral, lacks color charge and is massive, with antimatter counterparts;
* six massive spin-1/2 quarks that are electrically and color charged in three color charged variations each and antimatter variants;
* three spin-1/2 charged leptons that lack color charge, with antimatter counterparts;
* three spin-1/2 neutrinos that lack electrical or color charge,
* one massless electrically neutral spin-1 photons without color charge, with anti-matter counterparts;
* one massless electrically neutral, color charged spin-1 gluon that has their eight color charge variants;
* two massive electrically charged spin-1 W bosons without color charge which are antiparticles of each other; and
* a massive electrically neutral spin-1 Z boson without color charge.

Most non-SUGRA quantum gravity theories add one massless spin-2 graviton to the eighteen Standard Model particles.  The Standard Model lacks any particle that is a good dark matter candidate.  It would be possible to extend the Standard Model with quantum gravity to include a gravitino or right handed sterile neutrinos (and some boson to all their transition to other particle types or between each other), however, without otherwise disrupting the Standard Model.

The many particles predicted to exist in a Minimal Supersymmetric Standard Model aka MSSM (and almost all other less minimal SUSY models) are reviewed at Wikipedia.

In addition to a full set of Standard Model particles, the MSSM has five classes of superpartners: squarks (spin 0 bosons that are quark partners), sleptons (spin 0 bosons that are lepton partners), gluinos (spin 1/2 gluon partners), charginos (charged spin 1/2 superpartners of the W bosons and charged supersymmetric Higgs bosons), and neutralinos (four electrically neutral spin 1/2 that are mixes of the superpartners of the W bosons, Z bosons, and Higgs boson). There are also four additional Higgs bosons beyond those in the Standard Model (a positive charged spin zero Higgs ("H+"), a negatively charged spin zero Higgs (H-), a pseudo-scalar Higgs with neutral electric charge (usually denoted "A"), and an extra scalar Higgs with neutral electric charge that is either heavier or lighter than the Standard Model Higgs (usually denoted "H" for the heavier one and "h" for the lighter one).

Thus, the MSSM expanded into SUGRA has:
* six new scalar bosons that are color and electrically charged (the squarks) in three color charge variation each,
* five new scalar bosons are electrically charged but not color charged (the charged leptons, H+ and H-)
* five new scalar bosons electrically neutral and not color charged (the sneutrinos, h and A);
* one new electrically neutral spin 1/2 fermions (the gluinos) in eight color charge variations;
* four new charged spin 1/2 fermions (the charginos) that lack color charge;
* four new electrically neutral spin 1/2 fermions (the neutralinos) that lack color charge;
* one spin 3/2 fermion (the gravitino) that lacks electrical charge or color charge; and
* one massless spin-2 boson (the graviton).

The MSSM fermions presumably have anti-matter counterparts.

The MSSM conserves R-parity, which has one value of superpartners and the opposite value for non-superpartners, while this is broken dynamically in other SUSY models.  There are also SUSY theories that do not perfectly conserve R-parity, although these theories generally provide that the LSP decays to Standard Model particles in R-parity violating decays only very slowly, or with an LSP that is created from Standard Model particles almost as rapidly as it decays into Standard Model particles.

In all there are 25 BSM particles in the MSSM (ignoring color charge variants, antimatter variants of fermions, and parity variants of some or all fermions) and an additional 2 in SUGRA (although some people would call the graviton an "honorary" Standard Model particle as it is present in more or less identical forms in almost all supergravity theories) (ignoring antimatter variants of gravitinos, if any).

The are experimental hints of the existence of a graviton, but there are no experimental hints of the existence of any of the other 26 BSM particles in the MSSM and SUGRA.

The masses of these 26 BSM particles are key parameters, and another key parameter which related to the relationship between the H and h mass, and to the relationship between sfermion and sboson masses in SUSY called tan beta, is another key parameter.

None of the MSSM particles are stable except for the lightest supersymmetric particle which cannot decay further because R-parity prevents it from doing so.  The LSP then serves as a dark matter candidate.  The lightest neutralino and the gravitino are the most attactive as LSP candidates that are also good dark matter candidates because they are massive fermions, lack color charge and electric charge, and are stable.

Minimal supergravity (SUGRA) theories have the MSSM particles and also the graviton (massless, spin-2), and a gravitino (the massive, spin-3/2 superpartner of the graviton).  Non-minimal SUSY and SUGRA theories often have additional superpartners and non-Standard Model Higgs bosons.  Many also have right handed neutrinos and their superpartners, sometimes with a see-saw boson to handle interactions between left and right handed neutrinos that impart mass to neutrinos via a see saw mechanism, and most SUSY and SUGRA theories have Majorana rather than Dirac neutrinos, and conserve B-L number rather than conserving Baryon number and Lepton number separately.

BSM particle masses in SUSY and SUGRA theories.

The only massless BSM particle in the MSSM or SUGRA is the graviton which is also found in Standard Model extensions with quantum gravity.

Typically, the mass hierarchy of squarks and sleptons is inverted in SUSY models.  Third generation superpartners are the lighest, followed by second generation superpartners, followed by first generation superpartners.  Similarly, superpartners of bosons, which are fermions, all have masses greater than their Standard Model (or supersymmetric Higgs boson) counterparts.  The possibility that there are any superpartners that are lower in mass than any Standard Model counterparters of the same type has pretty much been completely ruled out experimentally.

This does not necessarily mean that the rank order of all Standard Model fermion partner masses is exactly inverted from the mass ranking of the particles in the Standard Model.  SUSY theories do not a priori demand, for example that a stau slepton be heavier than a stop squark.  But, to simplify matters, many more minimal SUSY models make this assumption.  In this case, for example, the lightest sfermion in such a SUSY theory will always be the stop squark, which helps to explain why the search for it is emphasized so heavily relative to other sfermion searches.

Also, since most dark matter theories prefer fermions to bosons as dark matter candidates, there should be at least one BSM SUSY fermion which is a partner of a Standard Model (or a partner of a SUSY Higgs boson or graviton) which is lighter than the stop squark (or than the lighest sfermion if different).  A SUSY theory in which the stop squark is the LSP is problematic when it comes to providing a good dark matter candidate.  Generally speaking, this means that either the lighest neutralino or the gravitino, or both, should be lighter than the stop squark.  Since neutralinos are linear combinations of superpartners of Standard Model particles with masses of 80 to 126 GeV, and experimental exclusions for neutralinos appear to be for masses greater than these, this puts an effective floor on the stop squark mass, in a model where the neutralino is the LSP dark matter candidate.  If the gravitino is the dark matter candidate (even if the neutralino is actually the LSP), then R-parity conservation for the neutralino is not necessary.

One particularly hot issue of scientific debate at the moment is whether there are any flaws in the methodology of SUSY particle searches that would allow any BSM particles in the MSSM or SUGRA with a mass of less than the Higgs boson or top quark to be missed by particle accelerator searches that purport to exclude BSM SUSY or SUGRA particles in the mass ranges.  Long lived BSM particles or particles with very low cross-sections of interaction could escape detection, but SUSY and SUGRA theories quite strongly constrain the cross-sections of interaction of the BSM particles that they mandate and provide a framework within which it is possible to qualitatively evaluate particle stability, although SUSY and SUGRA's many parameters do not allow for quantitative evaluations of this stability without additional assumptions about this parameter space not strongly supported by experimental data in any particular case.

Thus, a failure to detect a stop, sbottom, stau or tau sneutrino below a certain mass threshold generally also implies that this exclusion also applies lower generation squarks.  For example, conclusion that there are no stop squarks below 200 GeV would also imply that there are no scharm or up squarks below 200 GeV.

In SUSY theories, all gluinos should have identical masses, the charged Higgs bosons should have masses identical to each other, and the charginos should consist of pairs of particles with opposite charges and identical masses.  An exclusion of neutralinos below a certain mass is implied to exclude both the lighest neutralino and all of the other, heavier neutralinos.  The differences in couplings between the two scalar Higgs bosons in SUSY theories varies.

The New Search Results

* Stops squarks ("No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other considered stop decay scenarios, and generic upper limits are set on the visible cross-section for processes beyond the Standard Model.");

* third generation squarks ("A top squark of mass up to about 240 GeV is excluded at 95% confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded.");

UPDATE July 8, 2014: Another underwhelming analysis rules out a certain kind of stop squark with masses of under 180 GeV ("[F]or R-parity conserving supersymmetry . . . . Stop masses below ~ 180 GeV can now be ruled out for a light neutralino.") END UPDATE.

* superpartner particles generally ("No excess is observed with respect to the Standard Model predictions . . . Gluino masses up to 1340 GeV are excluded, depending on the model, significantly extending the previous ATLAS limits."); and

* more superpartner particles generally ("No excess above the Standard Model background expectation is observed in the various signal regions and 95% confidence level upper limits on the visible cross section for new phenomena are set. The results of the analysis are interpreted in several SUSY scenarios, significantly extending previous limits obtained in the same final states. In the framework of minimal gauge-mediated SUSY breaking models, values of the SUSY breaking scale Lambda below 63 TeV are excluded, independently of tan beta. Exclusion limits are also derived for an mSUGRA/CMSSM model, in both the R-parity-conserving and R-parity-violating case. A further interpretation is presented in a framework of natural gauge mediation, in which the gluino is assumed to be the only light coloured sparticle and gluino masses below 1090 GeV are excluded.").

Note that the natural SUSY breaking scale Lambda for a SUSY theory that naturally and fully solve the "hierarchy problem" which was one of the important reasons that SUSY was proposed in the first place is 1 TeV.  This is impossible when this Lambda value is at least 63 TeV.

Y1K: A Slice of Global History That Shaped The Modern World

The time period from around 900 CE to 1100 CE was an eventful one.

Austronesian mariners had reached their greatest extent having established their civilization as far as Easter Island (ca. 700 CE-1100 CE), New Zealand (some argue for dates as late as 1250 CE), Hawaii and Madagascar (ca. 350-1000 CE) (in the case of Madagascar together with people who were genetically similar to East African Bantus), and introduced a few South American crops like the kumara to Oceania (reaching the Cook Islands by 1000 CE).  Hawaii was first inhabited by Austronesian peoples ca. 300 CE, but around 1000 CE, immigrants from Tahiti called the Pa'ao, introduces a new dynasty of high chiefs, the Kapu system (a comprehensive set of strict religious laws), human sacrifce and the building of heiaus (temples).

The Tang dynasty and intermediate Five Dynasties and Ten Kingdoms Period gave way to the Song Dynasty (begun in 960 CE) in China.  The Song dynasty ruled all of China until 1127 CE after which it ruled Southern China until 1279 CE.  The Song dynasty was marked by a massive central state bureaucracy with posts filled on the basis of civil service exams that rivaled the former Roman Empire and contemporary Islamic empires in scope, but surpassed them in the modernity of its bureaucratic state.

The boundaries of modern Islamic South Asia were established, the Gypsies began their wanderings, and the linguistically Dravidian Brahui people migrated to Pakistan from Southern India.

Hindu Tagalog peoples created a sphere of cultural influence that reached from Hindu Middle Kingdoms in India to the Phillipines.  In Vietnam, the Hindu Kingdom of Champa (ca. 7th century CE to 1471 CE) flourished with significant cultural influence from India.  Cambodia's Khmer Kingdom (with its capitol at Angkor Wat) was also a Hindu Kingdom at the time (some later Kings would adopt Buddhism) and would enter its "Golden Age" around 1147 CE.  Thailand was ruled by a variety of Dvaravati principalities which were client states of the Khmer Kingdoms loosely allied with each other in a manner not dissimilar to the contemporaneous Holy Roman Empire in Europe.  In Western Java, the Hindu Sunda Kingdom (669 CE to 1579 CE) was in its heyday. The Medang Kingdom in Eastern Java vacillated between Hindu and Buddhist influences.  In the end, of course, Buddhist replaced Hinduism almost everywhere in Southeast Asia and East Asia.  The strong Hindu influences that persisted on the island of Bali in Indonesia are the only successors to this once far flung sphere of Hindu influence (similarly, the Mongolian Empire that rose and fell during Mongolia's late Middle Ages, a few centuries later, has left very little trace of its once vast Asian empire, linguistically or in modern institutions).

Around the same time, the city-state of Srivijaya in Sumatra, Indonesia, was a center of Buddhist expansion (another religion with its origins in India) in Southeast Asia and East Asia, which give rise to several Buddhist kingdoms (Kantoli, Srivijaya, Malyu, Pannai and Dharmasraya) that ultimately controlled all of Sumata within the framework of a larger Srivijaya empire.  But, this empire was fading around 1000 CE because improved maritime technology allowed ships to skip intermediate ports, and because the Chola state in Southern India attacked Srivijaya's distant city-state holdings. These kingdoms were hubs of maritime trade between India, China and Southeast Asia.

In the Mediterranean, the First Crusade, launched by the Pope in 1099 CE, established short lived Christian states in the Levant, Moors were expelled from Northern Iberia from ca. 1000 CE to 1099 CE (reaching Toledo in 1085 CE). Norman soldiers routed the Moors from Southern Italy. Malta acquired its Semitic language at the time. And, conquering Seljuk Turks made Turkey, Turkish speaking and had a roughly 8% population genetic impact on the region.  At its peak in 1092 CE, the Seljuk empire included almost all of the Levant, Asia Minor, the Fertile Crescent, the Southern Persian Gulf coast, the Southern Caucasus Mountain region, Iran, Afghanistan, and much of Central Asia.

This time period brought about the ethnogenesis of the Druze people of the Levant (ca. 1014 CE to 1043 CE after which they ceased trying to convert newcomers to their faith and turned inward), who may have been refugees from the arrival of the Turks in Iberia.  The linguistically Uralic Hungarian language dynasty consolidated their control over Hungary and converted to Christianity (in 1001 CE); their migration to Hungary was likely driven by Turkish expansion.  The Roman Catholic and Orthodox Christian churches finally formally split (ca. 1053-1054 CE), more than five hundred years after the fall of Rome.

Europe's last hunter-gatherers finally converted to farming and herding. The Holy Roman Empire, formed in 962 CE, was a loose alliance of principalities including most of modern Northern Italy and Germany. The Normans conquered England in 1066 CE.  The Viking sailors settled Iceland established one of the first parliaments, the Althing, in 930 CE, and under Lief Erickson, the Vikings established a short lived North American colony of Vinland.

Relict animist refugees from the Islamization of Northern Africa and the Sahel led to the ethnogenesis of the astronomy practicing Dogon people in defensible cliff dwellings on the banks of the Niger River in Mali. The Bantu expansion in sub-Saharan Africa reached its greatest extent in Southern Africa and would remain secure there through the present.

In the New World, the proto-Inuit Thule people entered North America from Siberia (ca. 500 CE to 1000 CE), possibly sharing a common origin with the expansion of linguistically Uralic people to the West. Some of the Na-Dene people migrated to the American Southwest ca. 1000 CE, giving rise to the Navajo among others, pushed by incoming Inuits and pulled by a power vacuum in the Southwest.  Mayan civilization collapsed ca. 950 CE as a result of an extreme drought. The Uto-Aztec language speaking Utes, possible pushed there by the outflows of people from the collapse of the Mayan civilization refugees then replaced the Great Basin's Fremont peoples. The Anasazi people in modern Arizona centered around a religious center a Chaco, developed a culture known for its sophisticated irrigation systems, its precision astronomy, its architecture that led to a baby boom unprecedented in history. The Mississippian culture with a capitol near modern Saint Louis attained regional population densities rivaling modern cities and had a sphere of cultural influence that extended throughout the Mississippi river basin and into the American Southwest as far as the Atlantic Coast of North Carolina.

The Cañari people of Ecuador, a small, but advanced civilization, flourished after the fall of the Mayans and before the rise of the Inca and Aztec cultures. And, in modern Acre State, Brazil, deep in the modern Amazonian rain forest, a culture that made massive geoglyphs fully visible only from thousands of feet in the air was in its prime, following in the footsteps of the Nazca Line culture of Peru, and the subsequent Andean Tiwanaku culture which also made geoglyphs.

This global ferment was driven in part by climate, the Medieval Warm Period from ca. 950 CE to 1250 CE. Arab astronomers, astronomers attached to the Song Dynasty Court in China, and astronomers in Chaco were witness to a very bright supernova in 1006 CE, to the supernova that created the Crab Nebula on the 4th of July in 1054 CE, and to Halley's Comet in 1066 CE.

Cosmic Ray Flux Related To Atmospheric Temperature

Cosmic rays, a term that includes not just photons but also fast moving particles headed towards Earth, would kill us all were it not for the protective shield provided by our atmosphere.  Analysis of cosmic rays hitting earth are also a key to trying to detect dark matter, the properties of neutrinos, and more.

Seasonal variation in these cosmic rays has often been proposed as a key to distinguishing dark matter derived signals from other data.  But, it turns out that the strength of the shield that the atmosphere provided against cosmic rays is a function of its temperature.

This makes sense.  But, a results from the MINOS experiment quantity this seasonal background factor based on differences in intensity of muon fluxes (which often are produced when cosmic rays strike the atmosphere).  This is important because is strongly suggests like seasonal variation in cosmic ray detection that might otherwise be assumed to be a significant signal, is really just due to atmospheric temperature variations.

Also, detection of sub-GeV energy dark matter signals requires that neutrinos and other cosmic ray backgrounds be well understood.  This kind of stepping stone makes that possible.

* * *

Precision measurements of neutrinos can also serve as a probe of Lorentz invariance violations (i.e. violations of special relativity), that are expected in some quantum gravity theories.  The experimental signatures of Lorentz invariance in neutrino experiments are discussed in another new paper.

Up Quark, Down Quark Mass Difference Known With Unprecedented Precision

The News

A June 18, 2014 paper estimates that differences in electromagnetic field strength between the proton and neutron account for 1.04 +/- 0.11 MeV of the proton-neutron mass difference using lattice QCD methods, an estimate three or four times more precise that previous state of the art estimates of this component.  The proton gets more of its mass from its electromagnetic field than the neutron does.  (An April 11, 2014 power point description of this paper is also available.)

The same paper estimates, using this calculation, that the difference between the up quark mass and the down quark mass is 2.33 +/- 0.11 MeV.  This is the most precise estimate of the up quark-down quark mass difference to date.  The previous state of the art estimate had a best fit value of 2.5 MeV (within the two sigma confidence interval of the new result), but with an uncertainty of about 0.7 MeV.

Some Details For Experts

The paper assumes that the difference in the strength of the strong force field between the proton and neutron is assumed to be negligible relative to the differences in quark masses and electromagnetic field strengths.  This seems intuitively reasonable, because up quarks and down quarks have identical strong force couplings to each other and both have very small masses relative to the total mass of a nucleon, while having very different electromagnetic couplings.

Put another way, QCD contributions to the mass splitting between the proton and the neutron are almost entirely a function of the difference between the rest masses of the up and down quarks.  This is true even though the gluon field accounts for more than 98% of the mass of protons and neutrons respectively, while the contributions of the rest masses of the quarks themselves is modest.

The dominant source of uncertainty in this estimate arises from lack of clarity over whether the dipole form factor of the inelastic subtraction term in the contribution of the electromagnetic field strength to the mass of the proton and neutron scales as a cubic or quartic polynomial (i.e. whether an exponent in an obscure subpart of the overall equation is 3 or 4).  If it is cubic, then the actual value is higher by 0.09 and the uncertainty drops from +/- 0.11 MeV to +/- 0.04 MeV.  If it is quartic, then the actual value is lower by 0.09 and the uncertainty drops by the same amount.

This paper replicated the result of another paper released in pre-print form by an independent group of lattice QCD investigators just two days earlier on June 16, 2014, using a moderately different approach, so the result can be considered quite reliable.  This paper's result for the difference in mass due to electromagnetic field strength between the proton and neutron is 1.00 MeV +/- 0.16 MeV, and an up quark-down quark mass difference of 2.52 MeV+/- 0.29 MeV.  But, it predicts a total difference between the proton and neutron mass of 1.51 +/- 0.28 MeV (compared to the physical value of 1.2933322 MeV), which is not inconsistent with experiment but has a central value that is high by about 16%.

Incidentally, while both papers have produced highly precise measurements of the difference in nucleon mass attributable to the electromagnetic field energy in these baryons, I am not able to cite any source regarding the absolute value of this contribution of the masses of the proton and neutron, relative to the contribution from the gluon field in these baryons (and to the extent that the two are interrelated this could conceivably be an ill defined quantity).

Both results exploit the Coleman-Glashow relation (which dates to at least 1982 or earlier) which argues that the sum of the mass differences in three different pairs of charged and neutral hadrons (one of which is the proton and neutron pair) with carefully chosen combinations of light scalar differences and other factors that cancel out due to symmetries, should equal zero.  This hypothesis is confirmed experimentally true to the current limits of experimental precision (something that a 2000 paper called a "miracle", but which flows quite naturally from the quark model of QCD and symmetry considerations).

The Masses And Mass Differences Of Exclusively or Predominantly Light Quark Hadrons

Protons and Neutrons

A neutron has a rest mass of 939.565,379(21) MeV.  A proton has a rest mass of 938.272,046(21) MeV. The difference between the rest mass of the neutron and the rest mass of a proton is known to somewhat greater precision; it is 1.293,332,2(4) MeV.

The rest mass of an electron is 0.510,998,928(11) MeV.

The difference between the rest mass of a neutron and the sum of the rest masses of a proton and an electron is 0.782,333,2(4) MeV.  In other words, this is the minimum energy of a photon produced in ordinary beta decay.  About one part in 1201 of the rest mass of a neutron is converted into energy in ordinary beta decay.  The other 1200 out of 1201 parts of the rest mass of a neutron is converted in other kinds of rest mass.

A neutron has one up quark and two down quarks, producing a zero net electric charge.  A proton has two up quarks and one down quark, producing a +1 net electric charge.  Both have total angular momentum equal to 1/2.

Quantum chromodynamics (QCD) estimates of the proton and neutron mass from first principles are accurate to about +/- 1% (i.e. about +/- 1 MeV), although QCD estimates of the proton-neutron mass difference are now significantly more precise than that (while still remaining far less precise than experimental measurements of this quantity).

Other Hadrons Made Up Only Of Up and Down Quarks

Due to confinement, no light quark is ever observed at an energy scale of less than that of a pion (about 140 MeV for charged pions and 136 MeV for neutral pions), which is the lightest particle made up of quarks, and the only pseudoscalar mesons (total angular momentum of o and negative parity) made up only of light quarks.

The vector mesons, with total angular momentum 1, that are made up only of up and down quarks are the rho mesons (vector) (cursive p) which has a mass of 775.11 MeV when charged and 775.49 MeV when neutral, and the omega mesons (vector) (cursive lowercase w) which has a mass of 782.65 MeV.

All four of the delta baryons, which are three quark particles made up of combinations of up and/or down quarks with total angular momentum 3/2 (unlike the 1/2 of the proton and neutron) have masses of about 1232 MeV.

The lighest scalar meson (with total angular momentum of 0 and positive parity), the f₀(500) has a mass of about 500 MeV and does not have a consensus interpretation of its makeup in a simple quark composite model, although it is sometimes interpreted as primarily consisting of linear combinations of pions, which are in turn made up only of up and down quarks.

Interpreting the Proton-Neutron Mass Difference

Some of the difference in rest mass between a neutron and proton may be attributable to a difference in mass between an up quark and a down quark.  Some of the difference in rest mass between a neutron and a proton may be attributable to a difference in the amount of energy in the strong force field and electromagnetic field in the proton and neutron respectively.

To only slightly oversimplify, using the canonical values for the up and down quark masses (discussed further below), the quarks in a proton (about 9.4 MeV) are 2.5 MeV lighter than in the neutron (about 11.9 MeV), but the proton has combined contributions of the strong force fields and electromagnetic fields that are 1.2 MeV stronger (928.9 MeV in the proton v. 927.7 MeV in the neutron), a difference of about a tenth of a percent in field strength.

The question of how much of this difference is due to differences between up quark and down quark rest masses, and how much of this differences is due to gluon and photon fields in the proton and neutron is highly model dependent.

The particle data group estimate of the mass difference between the up and down quarks is 2.5 MeV, rather than the 1.3 MeV that one would naively expect from the difference between the neutron mass and the proton mass, a value that would struggle to fit in the two sigma error bars of current estimates of absolute masses and mass ratios for these quarks.

According to the Particle Data Group, the up quark has an estimated mass of 2.3 MeV + 0.7/-0.5 MeV, and the down quark has an estimated mass of 4.8 MeV +0.5/-0.3 MeV.  Viewed together, rather than in isolation, the up quark rest masses is estimated to be from 0.38 to 0.58 of the rest mass of the down quark.  The precision with which we know the up and down quark masses is roughly ten million times less than the precision with which we known the difference in rest masses between the proton and neutron.  These estimates are little improved from estimates made at the very dawn of the quark model in the 1970s.

In late March or early April of 2010, a paper in Physical Review Letters by Christine Davies and others (pre-print here and pdf here) made a much more precise estimate of 2.01 +/- 0.14 MeV for the up quark and 4.79 +/- 0.16 MeV for the down quark, which implies a difference between the two rest masses of 2.78 +/- 0.21 MeV (and a low end 0.42 mass ratio), which is just barely consistent with the new results at the two sigma level.  But, the PDG worldwide average analysis has not proclaimed this result to be correct at that level of precision.

Definitional Issues In Light Quark Mass Determinations

Light Quark Pole Masses

Even the definitions of the light quark masses are fraught with problems.  In the Standard Model, the mass of a particle varies with the energy-momentum scale at which it is measured.  In the case of top quarks, bottom quarks, and charm quarks, it is possible and sensible to measure the "pole mass" of a particle - i.e. the mass of a quark measured at an energy scale equal to its rest mass.

In the case of the light quarks, the rest masses of the quarks are customarily evaluated at energy scales of 2 GeV (i.e. at about the mass of two nucleons that collide with each other), at which they are observed (in a confined context), rather than at the rest mass of the quarks themselves.

But, for example, extrapolation of the running of the quark masses suggests that the light quarks should be about 35% heavier at a 1 GeV energy scale.  Naively extrapolating the running of the light quark masses downward from 2 GeV to estimate their "pole mass" produces masses in the hundreds of MeVs, but a more accurately interpretation is that the pole masses of the light quarks are simply ill defined and the extrapolation is being applied beyond the scale where it is valid.  Instead, different definitions of quark masses than pole mass, such as the MS mass scheme are used to generalized the concept of quark masses to the light quarks.  But, it isn't obvious that MS mass is as fundamental a quantity as pole mass.

Koide (1994) calculates the running of the three light quark masses down to their pole masses, even though these values have little practical application, in both a five quark and three quark flavor model. In the five quark flavor model he comes up with pole masses for the up quark of 346.3 MeV, for the down quark of 352.4 MeV and for the strange quark of 489 MeV. In a three quark flavor model he comes up with pole masses of 163.1 MeV for the up quark, 169 MeV for the down quark, and 338 MeV for the strange quark. One could get somewhat lower light quark pole mass values still in a two quark flavor model. 

Koide updated these calculations in 1997 and concluded that the pole mass of the up quark was 0.501 GeV, the pole mass of the down quark was 0.517 GeV and the pole mass of the strange quark was 0.687 GeV (based on their measured values at other energy scales), although all sub-1 GeV values were noted with an "*" mark. 

A more recent update of the calculations can be found at Xing (2008) does not consider masses running to very low energy scales for light quarks, explaining that "The pole masses of three light quarks are not listed, simply because the perturbative QCD calculation is not reliable in that energy region."

Notably, these perturbative QCD calculations become ill defined at masses higher than the mass of the pion.  So, perturbative QCD calculations break down to the point of being unreliable at energy scales somewhere between 140 MeV and 1000 MeV.

The pole masses in the five quark flavor models are quite similar to the conventional dressed quark masses for the up and down quarks discussed below, however.

Dressed Masses For Light Quarks

Another approach is the look at the "dressed quark" mass which for the up and down quarks is about 0.32 GeV (i.e. about a third of the proton mass, which is the lightest three quark composite particle containing only light quarks), which includes a proportionate share of the gluon field mass of a baryon that contains a light quark in its mass.  This is also sometimes described as a "constituent quark model."  (The link in this paragraph is to a 2013 power point presentation that is quite a good starting point for understanding the state of the effort to determine the quark masses.)

Recent state of the art estimates of dressed quark masses determined with Lattice QCD, however, are closer to 0.25 GeV for up and down quarks, and 0.502 GeV for strange quarks.  This implies fundamental light quark masses of about 8.6 MeV and fundamental strange quark masses of about 227 MeV at an energy scale of about 840 MeV.  These values are about 2.45 times the canonical values for these masses at 2 GeV energy scales.  I may be misinterpreting this analysis, but this seems to me to indicate that the total contribution of the electromagnetic field of a proton to a proton's mass is about 188 MeV.

While "dressed quark" masses for the up and down quark can produce not obviously wrong estimates of hadron masses for most hadrons containing just up and down quarks (and also, for example, for the eta meson which is a mix of up, down and strange quarks with a mass of 547.85 MeV).

But, dressed quark masses for the up and down quarks do seem inconsistent with the masses of the pions.  Charged pions have two light quarks but have a mass less than the dressed mass of even one light quark, and neutral pions which are linear combinations of up-antiup and down-antidown quark pairs are even lighter.  In constituent quark models, the binding energy of the pion implied by the dressed quark masses for the up and down quarks must be approximately negative 360 MeV.  But, it isn't obvious that negative energies are are a physical concept in this context.

An alternate way of understanding the light hadron masses which explains why the pion can be so light is explained in a fairly straightforward way here.  Pions play a special role as "Goldstone" bosons in QCD, i.e. force carriers who arise as a result of a broken symmetry, which give them special properties.

Basically, the right formula for the mass of a meson is equal to a constant scale factor times the positive square root of ((two times the average mass of the quarks in the meson) times (the appropriate value for the QCD scale)).  The QCD scale value, in turn, is a function of the number of quark flavors that are accessible at the energy level involved.  It is about 217 MeV when there is sufficient energy to involve five active quark flavors and abut 350 MeV when there is sufficient energy to involve three active quark flavors.  Arguably, it may be necessary in some cases to invoke a two active quark energy scale, although this involves complex self-referential calculations related to the strange quark mass.

Footnote

Another interesting amateur mass hierarchy paper with a numerological flair can be found here.

UPDATED July 2, 2014 for formatting purposes and to add material to the definitions section of this post.

Stray Physics Musings

* In the simple Platonic ideal, a black hole is a singularity from which not even light can escape.  In other words, photons can't cross the event horizon.  In this ideal, whether or not the matter and energy sucked up by a black hole had a net electric charge, the electric and magnetic fields generated by particles with electric charge would not escape the black hole because the photons that give rise to those fields would be trapped behind the event horizon.

Now, we know empirically, there is a strong magnetic field in the vicinity of Sagittarius A*,  the black hole at the center of the Milky Way.  The only way this could be possible in the Platonic ideal of a black hole is if the magnetic field is generated by the movement of charged particles just outside the event horizon as they are pulled toward the black hole.

Now, in an ad hoc blend of General Relativity reasoning and quantum mechanics reasoning, have concluded that black holes are leaky, and rather than preventing anything from escaping at all, actually emit Hawking radiation.  But, it doesn't necessarily follow that Hawking radiation is large contributor to the magnetic field around black holes that are observed.

* In principle, mesons and baryons have an infinite number of excited, higher energy states with higher masses than the ordinary versions of these hadrons.  It appears, in contrast, the fundamental fermions come in exactly three generations, rather than an infinite number, which means that an intuitive sense of higher generation fundamental fermions as excitations in the same sense as excited states of hadrons is probably flawed - unless the same process is at work but there is some competing factor that places an upper bound on the amount of excitation that a fundamental fermon can have, but not on a hadron (at least at the energy scales we can observe - one could image that there is exactly some fundamental number of excited states much greater than three that are possible for any given hadron at energies to high to observe).

Many factors argue in favor of exactly three generations with current experimental evidence.  There are direct lower limits on the possible mass of each of the four possible kinds of fourth generation fundamental fermions.  There are also strong theoretical considerations that require each generation to have a complete set of four fundamental fermions.

In ratio of limit to mass of third generation fermion, the bound is greatest in the case of the neutrinos.  The practical upper bound on the mass of the heaviest Standard Model neutrino rest mass eigenstate is on the order of 0.1 eV/c^2.  The lower bound on the mass of a fourth generation neutrino is about 45,000,000,000 eV/c^2.  The ratio of the two masses is 450,000,000,000 to 1.  This is profoundly greater than any of the ratios of masses between a particle of one generation and a particle of the next generation among the three generations of four kinds of Standard Model fermions.

* The Higgs field couples to the rest mass of massive Standard Model particles.  But, unlike gravity, it does not couple to mass arising from gluon fields in hadrons, to gluons, to photons, to kinetic energy, to angular momentum, to pressure, or any other quantity besides rest mass that gravity impacts in General Relativity.  Yet, since General Relativity describes gravity, and the gravitational effects of rest mass swamp all other sources of gravity in most circumstances, General Relativity must have some fairly deep relationships to the Higgs field.  But, the Higgs vacuum expectation value has no seeming correspondence to the cosmological constant aka dark energy.

* The most definitive evidence we have for dark matter comes from comparing the behavior of objects observed by astronomers with the behavior we would expect if only General Relativity applied.  I strongly suspect that this kind of evidence will be the most powerful means of ultimately discriminating between potential models explaining the mechanism of these effects.

For example, we are very near to having a detailed precision map of the shape of the Milky Way dark matter halo that is inferred from a clever method of exploiting the movement of a handful of very special stars which when measured precisely reveal this information in an elaborate variant on triangulation.  Increasingly precise measurements of the shape and size of the Milky Way's dark matter halo already permit quite precise estimates of the matter density of dark matter in the vicinity of our sun, which fixes on key parameter in direct dark matter detection experiments.  Knowing this from direct halo observations eliminates the model dependence of dark matter detection experiments that merely assume a theoretically estimated dark matter density in our vicinity.  Only the mass of individual dark matter particles and their cross section of interaction remain to be determined.

Current methods have come up empty in the GeV mass vicinity down to very low cross sections of interaction, and to move to lower mass candidates need to better distinguish and characterize neutrino and cosmic ray backgrounds, although good progress is being made on these fronts.  Of course, all is for naught if dark matter is genuinely collisionless, at least with matter other than other dark matter.

Accelerator experiments like the LHC also narrow the dark matter particle parameter space.  These experiments have likewise come up empty.  This strongly disfavors dark matter that interacts via any of the three Standard Model forces, again suggesting that it may be effectively collisionless if it is fermionic (the leading theory) except for Fermi contact forces (since fermions can't occupy the same space at the same time), and any dark matter specific interactions.  The lack of Standard Model forces or particles, or General Relativistic equation terms to explain dark matter is really frustrating.  We are missing something huge and we don't know why.

There are some hints at dark matter annihilation, but these are very model dependent and assume we know about all possible sources of cosmic ray signals when we don't.

Computer models that show what the universe would look like given various dark matter properties are also making great strides as greater computational power becomes available.