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Tuesday, May 31, 2016
John Hawks On Neanderthal Stone Circles
John Hawks muses at length on Neanderthal stone circles recently discovered deep in a cave. His main point is that given that much smaller average population of Neanderthals at any one time, and their greater remoteness in history, it isn't surprising that the archaeological record that might shed light on their culture is thin.
More Quick Hits
* Celtic parts of the U.K. (presumably Scotland, Wales, Northern Ireland), have more steppe ancestry than Southern and Eastern England proper, presumably because Norman invaders ca. 1066 CE had less steppe ancestry than the pre-existing residents of the U.K. The residents of English proper also have less steppe ancestry than Anglo-Saxon ancient DNA. Keep in mind, however, that this is a subtle difference that is discernible only because of a huge sample size (N=113,851) in a generally very homogeneous population.
* 48 ancient genomes from Iron Age to 18th century Finland will be available before year end.
Thursday, May 26, 2016
Ancient Phoenician mtDNA Looks European
The mito-genome of a Carthaginian Phoenician has been sequenced...The Tunisia man had the maternal haplotype U5b2c1, which is fairly limited to Europe. It is also found in low frequency in the Phoenician heartland of Lebanon, which was either native there as well or it was cross-pollinated through its colonies in Western and Southern Iberia. Additional sequencing shows some affinity to a person from Portugal.From Bell Beaker Blogger.
Wednesday, May 25, 2016
Trying To Mix Physics and Religion Can Get Embarassing
Letting money from religiously motivated people drive discussions of physics can lead to absurd crazy-talk.
For those of you who aren't familiar with it, the Everettian interpretation of quantum mechanics is another name for the "Many Worlds Interpretation".
The "fine-tuning" argument argues that physical constants in our current version of the laws of the universe which are derived from a variety of other physical constants, must have precise and absurdly "unlikely" values to cancel out and produce the measured values.
Every now and then I consider absurd questions too, like whether unicorn meat would be kosher. But, I don't try to hold legitimate academic mini-conferences discussing the issue.
From Not Even Wrong.Some people at Rutgers have decided to show what can go wrong when you have the Templeton Foundation funding “philosophy of physics”. They’ve scheduled a two-day Rutgers Mini-Conference on Multiverse, Theodicy, and Fine-Tuning, during which the speakers will consider the following two topics:
- Everettian Quantum Mechanics and Evil
The problem of evil has been around for a long time: How can an all-powerful and all-good God allow evil of the sorts we see in the world? If the Everettian interpretation of quantum mechanics is correct, though, then there is a lot more evil in the world than what we see. This suggest a second problem of evil: If Everettianism is true, how can an all-powerful and all-good God allow evil of the sort we don’t see?- A Probability Problem in the Fine-Tuning Argument
According to the fine-tuning argument: (i) the probability of a life-permitting universe, conditional on the non-existence of God, is low; and (ii) the probability of a life-permitting universe, conditional on the existence of God, is high. I demonstrate that these two claims cannot be simultaneously justified.
For those of you who aren't familiar with it, the Everettian interpretation of quantum mechanics is another name for the "Many Worlds Interpretation".
The "fine-tuning" argument argues that physical constants in our current version of the laws of the universe which are derived from a variety of other physical constants, must have precise and absurdly "unlikely" values to cancel out and produce the measured values.
Every now and then I consider absurd questions too, like whether unicorn meat would be kosher. But, I don't try to hold legitimate academic mini-conferences discussing the issue.
Quick Hits
Busy with work and fighting an eight week old spring cough, so I'll be brief:
* Ny's arya blog has an interesting post about the linguistic evidence that the proto-Indo-European homeland had lots of tall mountains, contra the stereotype of proto-Indo-Europeans as purely steppe people. Likewise, there is lots of sedentary agricultural vocabulary in proto-Indo-European.
This blog also pointed me to a nice meaty article (pdf) on the latest thinking about the Tocharian languages (the easternmost and now extinct branch of the Indo-European languages) by J.P. Mallory, a leading expert in the field.
* There is a new linguistics paper on Dene-Yeniseic by the main proponent of the case that the two language families (one Old World and one New World) are linguistically related.
* Someone found a beer recipe from China ca. 3000 BCE.
* Corded Ware women were more mobile than men per Strontium analysis of remains.
* British Bell Beaker people were mobile within Britain but not so much beyond it. Many more findings from the same paper are discussed here. And, Beaker people were all over the British Isles:
* In the course of a discussion at Razib's blog over whether Muhammed could have been a Christian or Christian influenced, I did some research on and learned a lot about the Parthian Empire which is relevant to a lot of Iron Age history. The discussion by Razib, me and multiple others is worth reading and brings out both stark differences of opinion in fact, subtle differences of opinion on importance and characterization of the facts, and plain old lots of historical data points from all sides that you probably didn't hear about, or don't recall, from Western Civ. My usual focus is pre-Iron Age, but I'm intrigued enough to look more closely into this period.
* I've been largely convinced that you can't meaningfully estimate how many genes influence a continuous genetically determined trait by looking at the genetic variance and assuming that due to the law of averages, if a trait is determined by a large number of genes then it will have low variance in a population. This is true, at the most basic level, because the law of averages applies only to repeated trials with the same probability and effect, while additive genetic variance does not meet this condition.
* Analysis of whole genomes from all over the world by software that allows for admixture tend to show that South Asians and East Eurasians mostly descend from West Africans with material East African admixture. But, its hard to know what to make of that as the software is really operating to deal with issues beyond the range of applicability where it is designed to function properly and can't necessarily consider all hypotheses that make sense to explain the data.
* Humans were hunting mastodons in Florida ca. 14,550 years ago (pre-Clovis).
* Fifteen Indus River Valley civilization remains have been sent to labs for ancient DNA analysis and someday we'll learn what they can tell us about that civilization whose population genetic connection with West Eurasia and South Asia is highly disputed. But, it could take awhile.
* Brown bears and modern humans migrated to similar places over the last 40,000 years (pre-agriculture) based upon brown bear genetics. Mammoth herd migration and genetics are similar informative regarding Paleolithic era human migrations. See also data points on elk.
* Donkeys were late arrivals to Europe, but donkey remains were found from 2500 BCE in Iberia.
* Somebody has unearthed a Dutch Bell Beaker boardwalk along a river.
* Bronze Age instrument construction involved very long range trade networks and the instruments themselves were widely disperse.
* The geology of the Andaman Islands explained.
* Ny's arya blog has an interesting post about the linguistic evidence that the proto-Indo-European homeland had lots of tall mountains, contra the stereotype of proto-Indo-Europeans as purely steppe people. Likewise, there is lots of sedentary agricultural vocabulary in proto-Indo-European.
This blog also pointed me to a nice meaty article (pdf) on the latest thinking about the Tocharian languages (the easternmost and now extinct branch of the Indo-European languages) by J.P. Mallory, a leading expert in the field.
* There is a new linguistics paper on Dene-Yeniseic by the main proponent of the case that the two language families (one Old World and one New World) are linguistically related.
* Someone found a beer recipe from China ca. 3000 BCE.
* Corded Ware women were more mobile than men per Strontium analysis of remains.
* British Bell Beaker people were mobile within Britain but not so much beyond it. Many more findings from the same paper are discussed here. And, Beaker people were all over the British Isles:
* In the course of a discussion at Razib's blog over whether Muhammed could have been a Christian or Christian influenced, I did some research on and learned a lot about the Parthian Empire which is relevant to a lot of Iron Age history. The discussion by Razib, me and multiple others is worth reading and brings out both stark differences of opinion in fact, subtle differences of opinion on importance and characterization of the facts, and plain old lots of historical data points from all sides that you probably didn't hear about, or don't recall, from Western Civ. My usual focus is pre-Iron Age, but I'm intrigued enough to look more closely into this period.
* I've been largely convinced that you can't meaningfully estimate how many genes influence a continuous genetically determined trait by looking at the genetic variance and assuming that due to the law of averages, if a trait is determined by a large number of genes then it will have low variance in a population. This is true, at the most basic level, because the law of averages applies only to repeated trials with the same probability and effect, while additive genetic variance does not meet this condition.
* Analysis of whole genomes from all over the world by software that allows for admixture tend to show that South Asians and East Eurasians mostly descend from West Africans with material East African admixture. But, its hard to know what to make of that as the software is really operating to deal with issues beyond the range of applicability where it is designed to function properly and can't necessarily consider all hypotheses that make sense to explain the data.
* Humans were hunting mastodons in Florida ca. 14,550 years ago (pre-Clovis).
* Fifteen Indus River Valley civilization remains have been sent to labs for ancient DNA analysis and someday we'll learn what they can tell us about that civilization whose population genetic connection with West Eurasia and South Asia is highly disputed. But, it could take awhile.
* Brown bears and modern humans migrated to similar places over the last 40,000 years (pre-agriculture) based upon brown bear genetics. Mammoth herd migration and genetics are similar informative regarding Paleolithic era human migrations. See also data points on elk.
* Donkeys were late arrivals to Europe, but donkey remains were found from 2500 BCE in Iberia.
* Somebody has unearthed a Dutch Bell Beaker boardwalk along a river.
* Bronze Age instrument construction involved very long range trade networks and the instruments themselves were widely disperse.
* The geology of the Andaman Islands explained.
Tuesday, May 17, 2016
mtDNA R0 is Native to Arabia
A new paper makes a very solid case that mtDNA R0, which is the sister clade to mtDNA HV (which is the dominant West Eurasian and North African Berber mtDNA clade) has a source in Arabia. It has maximum diversity there in addition to most clades being most common there. R0 is mostly found in Arabia and to a lesser extent West Asia, but mtDNA R0a1 is found at low frequencies across Europe as well and it as well as mtDNA R0a2'3 dispersed in the Mesolithic a.k.a. Epipaleolithic a.ka. 17kya to 13kya or so.
The full story is more complicated but generally fits a Mesolithic dispersal from Arabia which would have served as a refuge during the Last Glacial Maximum ca. 20kya.
The subclade mtDNA R0a2b2 is strongly associated by location, proximity, and age with the Ethio-Semitic migration from Arabia to East Africa, while R0a2b1 which strongly overlaps with it geographically, could be part of the same migration but might be from an earlier wave of Arabian to East African migration as the clade is two and a half times older than R0a2b2 along with a couple of other rare mtDNA R0 clade of the same age.
A rare clade mtDNA R0a6 is found mostly in Pakistan, mostly in the Kalash, but single individuals with this clade have also been noted in Iran, Palestine and Italy.
The full story is more complicated but generally fits a Mesolithic dispersal from Arabia which would have served as a refuge during the Last Glacial Maximum ca. 20kya.
The subclade mtDNA R0a2b2 is strongly associated by location, proximity, and age with the Ethio-Semitic migration from Arabia to East Africa, while R0a2b1 which strongly overlaps with it geographically, could be part of the same migration but might be from an earlier wave of Arabian to East African migration as the clade is two and a half times older than R0a2b2 along with a couple of other rare mtDNA R0 clade of the same age.
A rare clade mtDNA R0a6 is found mostly in Pakistan, mostly in the Kalash, but single individuals with this clade have also been noted in Iran, Palestine and Italy.
Wednesday, May 11, 2016
Einstein Published Theory Of General Relativity 100 Years Ago Today
The details are here. The theory was presented at a conference presentation in November of 1915, but the paper was submitted in March of 1916 and was published on May 11, 1916. Astonishingly little has changed in the theory of gravity since then (there have been refinements and applications of it, but not many).
In other news, the LHC is up and running again after a weasel induced shutdown. Grad students have been put on weasel patrol to prevent a repeat of the shutdown.
In other news, the LHC is up and running again after a weasel induced shutdown. Grad students have been put on weasel patrol to prevent a repeat of the shutdown.
For the nearest future, the plan is to have a few inverse femtobarns on tape by mid-July, which would roughly double the current 13 TeV dataset. The first analyses of this chunk of data should be presented around the time of the ICHEP conference in early August. At that point we will know whether the 750 GeV particle is real. Celebrations will begin if the significance of the diphoton peak increases after adding the new data, even if the statistics is not enough to officially announce a discovery. In the best of all worlds, we may also get a hint of a matching 750 GeV peak in another decay channel (ZZ, Z-photon, dilepton, t-tbar,...) which would help focus our model building. On the other hand, if the significance of the diphoton peak drops in August, there will be a massive hangover...
Tuesday, May 10, 2016
A Moment Of Silence For Marcus
His Online Icon (via Mad Magazine)
I never met Marcus in person, but I discussed physics with him at the Physics Forum bulletin board where he presided over the Beyond the Standard Model forum with a special focus on loop quantum gravity (as well as other areas of physics where we shared interests) on countless lengthy occasions for about twelve years and he was always a perfect gentleman while also having great insights into physics. He was a great mentor and friend. He joined the board about a year before I did and in that time made about 25,000 comments and started 757 discussion threads.
It is with a heavy heart that I report that he has died of cancer (Friday or thereabouts). According to his son, "it was esophagus cancer -- we found out about it in September, but by that point it was advanced to a level where not much could be done. We tried anyway -- chemo, radiation, etc. But, well..."
It is a sad day worthy of a moment of silence to reflect on what we shared. The world is less wonderful without him.
Higher Primates Mostly Went Extinct In Asia When India Crashed Into Asia
Primates (per Wikipedia) can be broken down into a number of clades, one of which is called Simiformes (aka "anthropoids") which excludes tarsiers, lemurs and lorises (the so called "lower primates"), but includes humans, chimpanzees, gorillas, orangutans, gibbons, Old World Monkeys and New World Monkeys.
A new study, cited below, out of China provides insights into why "higher primates" survived and evolved into various clades including humans in Africa, while they went extinct leaving only "lower primates" in Asia.
The key event took place 34 million years ago when the collision of the continental plate that is now the Indian subcontinent hit the rest of Asia resulting in climate changes that destroyed jungles that had been home to primates until then. "Lower primates" managed to survive in the less lush forests that remained, while "higher primates" could not survive without a thriving tropical jungle.
The new paper is:
X. Ni et al. "Oligocene primates from China reveal divergence between African and Asian primate evolution." 352 Science 673 (May 6, 2016).
A new study, cited below, out of China provides insights into why "higher primates" survived and evolved into various clades including humans in Africa, while they went extinct leaving only "lower primates" in Asia.
The key event took place 34 million years ago when the collision of the continental plate that is now the Indian subcontinent hit the rest of Asia resulting in climate changes that destroyed jungles that had been home to primates until then. "Lower primates" managed to survive in the less lush forests that remained, while "higher primates" could not survive without a thriving tropical jungle.
A sharply cooler and drier climate at that time, combined with upheavals of landmasses that forged the Himalayas and the Tibetan Plateau, destroyed many tropical forests in Asia. That sent surviving primates scurrying south, say paleontologist Xijun Ni of the Chinese Academy of Sciences in Beijing and his colleagues. New Chinese finds provide the first fossil evidence that the forerunners of monkeys, apes and humans, also known as anthropoids, were then largely replaced in Asia by creatures related to modern lemurs, lorises and tarsiers. . . .
“The focal point of anthropoid evolution shifted at some point from Asia to Africa, but we didn’t understand when and why the shift occurred until now,” says paleontologist and study coauthor K. Christopher Beard of the University of Kansas in Lawrence.
But the scarcity of Asian primate fossils from that time relative to those from Africa leaves the matter unsettled. Egyptian sites in particular have yielded numerous primate fossils dating from around 37 million to 30 million years ago.
Excavations from 2008 to 2014 in southern China produced 48 teeth, some still held in jaw fragments, from six new fossil primate species, Beard says. These primates were tree dwellers and had assembled in a region located far enough south to retain forested areas. The new finds provide a rare glimpse of Asian primates that managed to weather the climate shift. Fossil teeth of one ancient species look much like those of modern tarsiers. These tiny, bug-eyed primates now live on Southeast Asian islands. “Tarsiers are ‘living fossils’ that can trace their evolutionary history back tens of millions of years in Asia,” Beard says.
Only one Chinese fossil primate comes from an anthropoid, Ni’s group concludes. The researchers classify that animal as part of a line of Asian anthropoids previously identified from roughly 40-million-year-old tooth and jaw fragments found in Myanmar, just across China’s southwestern border (SN: 10/16/99, p. 244).
Only one other Asian site, in Pakistan, has yielded anthropoid fossils of comparable age to the Chinese finds. The Pakistan fossils consist solely of teeth. Asian anthropoids died out a few million years after the continent’s tropical forests began to shrink, Beard suspects.
Investigators already knew that primates’ forest homes in Africa survived the ancient cool down better than those in Asia.The Chinese team also argues, with less definitive support, for an asian origin of higher primates around 55 million years ago. But, "Lemur and loris ancestors must have lived in equatorial Africa and Madagascar by 34 million years ago, as lemurs and loris relatives do today. . . . The oldest known primate fossils, from 56 million to 55 million years ago, come from Asia, Europe, Morocco and North America." So, it is much harder to determine where primates, in general, first evolved.
The new paper is:
X. Ni et al. "Oligocene primates from China reveal divergence between African and Asian primate evolution." 352 Science 673 (May 6, 2016).
Is The 750 GeV Resonance Real? I Don't Think So
Hundreds of papers have been written about an apparent 750 GeV diphoton resonance seen at some moderate significance by both of the LHC experiments which Lubos likes to call the Cernette.
These bare facts would suggest a boson rather than a fermion (since the spin of the decay products is even), probably of spin-0 or spin-2 (because spin-1 bosons can't decay to two photons), and an intermediate electrically charged state of an otherwise electrically neutral particle, so it can couple to photons.
A second round of experimental data earlier this year confirmed initial indications of a "bump" that was too mild to be sure evidence of a new particle, but could conceivable be one, with a possible secondary Z boson-photon bump at 375 GeV.
The data are inconclusive at this point on the question of whether this resonance is narrow or wide (resonances are graphed as bell curves with a peak at the mass of the particle and a width measured half way up the peak at nearby masses that corresponds to the mean lifetime of the particle).
This paper from January which was updated last week, makes the case for a 4 sigma local significance, before considering look elsewhere effects, resonance with a narrow width and spin-0 (that also couples to gluons and hence must have strong force color charge as well). It notes that:
Despite the superficial similarities of a spin-0 750 GeV particle to a Higgs boson, the resonance is very un-Higgs like. For example, the primary decay of the Higgs boson is to b quark pairs, even though the diphoton channel is easier to see. And, pairs of b quarks with 371 GeV of momentum (plus 4 GeV or so of rest mass) would be hard to miss.
Lubos who is a bit generous about fitting the data to numbers because he thinks this is probably real (he gives it a 50% chance of being real), also asks his readers to:
But, of course, if you had a top quark-top antiquark composite particle, you ought to be seeing decays predominantly to pairs of b quarks and not to photons and Z bosons the way you do when pairs to top quarks that aren't bound to each other in hadrons are product. To get those decays you'd need toponium to experience a matter-antimatter annihilation to photons before the constituent top quarks could experience weak force decay. And, you'd probably want a process that produces the toponium from extremely high energy gluon fusion or something like that. (Glueball annihilation is also naively attractive, but the predicted glue ball masses aren't anywhere near a 750 GeV resonance; they're much too light.)
The diphoton channel at that energy level doesn't have a lot of potential background noise, so even a pretty modest number of diphoton detections at that energy scale could be significant.
But, there are hundreds of papers, rather than just a few leading ones, because a resonance at this mass, with the characteristics it has and the lack of strong signals in other channels at the same energy level, is not very well motivated in any of the leading extension of the Standard Model of particle physics. Also, the different data sets used to infer its existence are in some tension with each other.
For the most part, models that can accommodate a particle that decays to a 750 GeV diphoton resonance while having few other decay modes, require the existence of whole classes of other new particles to go with it (even if it is composite, rather than fundamental). This gives rise to a very baroque new beyond the Standard Model theory.
For that reason, despite the notability of the bump statistically, my money is on this turning out to be a statistical fluke or systemic experimental error, rather than an actual new particle.
We'll learn if this prediction is right or not within a year or two, depending on how many more weasel, baguettes and other mishaps interfere with the LHC experimental schedule.
These bare facts would suggest a boson rather than a fermion (since the spin of the decay products is even), probably of spin-0 or spin-2 (because spin-1 bosons can't decay to two photons), and an intermediate electrically charged state of an otherwise electrically neutral particle, so it can couple to photons.
A second round of experimental data earlier this year confirmed initial indications of a "bump" that was too mild to be sure evidence of a new particle, but could conceivable be one, with a possible secondary Z boson-photon bump at 375 GeV.
The data are inconclusive at this point on the question of whether this resonance is narrow or wide (resonances are graphed as bell curves with a peak at the mass of the particle and a width measured half way up the peak at nearby masses that corresponds to the mean lifetime of the particle).
This paper from January which was updated last week, makes the case for a 4 sigma local significance, before considering look elsewhere effects, resonance with a narrow width and spin-0 (that also couples to gluons and hence must have strong force color charge as well). It notes that:
1. The required cross section to fit the anomaly reported by ATLAS is in tension with the 8 TeV results, as well as the required cross section to fit the CMS anomaly.
2. Combining all data sets yields a local significance of ∼ 4.0σ for a 750 GeV spin-0 resonance produced through couplings to gluons or heavy quarks. While quoted statistical significances must be taken with a grain of salt, as they are obtained using binned data without inclusion of systematic errors, I find the combination yields a net increase in the statistical significance as compared to the ATLAS data alone.Some theorists have also hypothesized that this is really a quad-photon resonance with pairs of photons so close to each other that they register as single photons in the detectors.
3. The spin-2 interpretation is mildly disfavored compared to a spin-0 mediator. This is due to correlations in the photon momenta which results in a relative decrease in the ATLAS acceptance compared to CMS.
4. The combination of ATLAS and CMS 13 TeV data has a slight statistical preference for a spin-0 mediator with a natural width much smaller than the experimental resolution, as compared to the Γ = 45 GeV preferred by ATLAS alone. When the 8 TeV data is added, there is a slight statistical preference for a wide resonance over the narrow option, as it is easier to hide a wide resonance in the 8 TeV background. . . .
When considering the 750 GeV diphoton excess, the theoretical community must balance its natural exuberance with the recognition that the statistical size of the anomalies are very small. As a result, any further slicing of data will yield at best modest statistical preferences for the phenomenological questions that we in the community want answers to. That said, given that this excess is the most significant seen at the LHC since the discovery of the 125 GeV Higgs, and the resulting avalanche of theoretical papers which shows no sign of slowing, it is still a useful exercise to carefully analyze the available data and determine what we do – and do not – know at this stage. While there is some useful information to be gleaned from this exercise, we are fortunate that the continuation of Run-II will be upon us shortly.
From the existing data, we can conclude the following:
1. Explaining the anomaly through a spin-0 resonance is preferred over a spin-2 mediator, though this preference is less than 1σ in most cases.
2. Combining the 8 and 13 TeV data from ATLAS and CMS sets yields a ∼ 4.0σ statistical preference for a signal of ∼ 4(10) fb, assuming a narrow (wide) spin-0 resonance. This ignores the look-elsewhere effect, as discussed. Given that the significance of my fits to individual ATLAS and CMS data-sets are underestimates when compared to the full experimental results, it is possible that the actual statistical preferences are larger than these quoted values. However this would require a combined analysis performed by the ATLAS and CMS Collaborations.
3. The cross sections needed for the Atlas13, Cms13, and Cms13/0T data sets are incompatible at the two sigma level, though they agree in mass. The most straightforward reading of this (while maintaining a new physics explanation for the anomalies) is that the larger Atlas13 cross section constitutes a modest upward fluctuation from the “true” cross section, which is more in line with the Cms13 value. The reverse is also possible of course, but would bring the diphoton excess in the 13 TeV data in greater tension with the 8 TeV null results.
4. When considering only the 13 TeV data, the Cms13 data does not share the Atlas13 preference for a 45 GeV width. I find that the “wide” interpretation of the resonance has a statistical significance in the combo13 data set which is approximately 0.5σ less likely than the “narrow” interpretation. The corresponding likelihood ratio shows no preference for either width. Thus, while the theoretical challenge of a wide resonance may be appealing, the data in no way requires any new physics explanation to have the unusually large width of Γ ∼ 45 GeV.
5. Combining the 13 TeV data with the 8 TeV, I find that gluon-initiated mediators are preferred, due to having the largest ratio of relevant p.d.f.s. In particular, the combination of all six data sets for a gluon-initiated narrow resonance has the same statistical preference for a signal as the Combo13 data alone does, though the best-fit cross section decreases slightly when the 8 TeV data is added (∼ 4.0σ for a ∼ 4 fb signal). In the narrow width assumption, heavy quark-initiated mediators have slightly smaller statistical preference, and a light-quark coupling has a fairly significant decrease in statistical preference, indicating a more serious conflict between the 13 and 8 TeV data.
6. Combining the 13 and 8 TeV data sets under the Γ = 45 GeV spin-0 model increases the statistical preference for signal as compared to the Combo13 result, as the excess can be more easily absorbed by the background model here. Combining all the data sets in this way results in a ∼ 3.5σ preference for a ∼ 10 fb signal (a 0.5σ increase over the Combo13 wide-resonance fit), with a likelihood ratio of ∼ 20 rejecting the narrow interpretation. Again, these statistical preferences are relatively small, thus theorists are free to explore the options, but should keep in mind that the experimental results are inconclusive.
The conclusions of this paper are perhaps not a surprise. There is clear tension between the Atlas13 and Cms13 results, as well as with the non-observation in 8 TeV data. The question of the width is especially puzzling; but further slicing of the data, as I have demonstrated, leads to somewhat conflicting results which do not have a clear statistical preference towards any one solution. I note that if the ATLAS excess is indeed an upward fluctuation from a signal which is more in line with the Cms13 value, then perhaps this could also give a spurious signal of large width. However, the true answers will only come with more data, though I note that, if the signal is indeed real, but on the order of 4 fb, then we may need 10-20 fb−1 for a single experiment to have 5σ discovery.
Despite the superficial similarities of a spin-0 750 GeV particle to a Higgs boson, the resonance is very un-Higgs like. For example, the primary decay of the Higgs boson is to b quark pairs, even though the diphoton channel is easier to see. And, pairs of b quarks with 371 GeV of momentum (plus 4 GeV or so of rest mass) would be hard to miss.
Lubos who is a bit generous about fitting the data to numbers because he thinks this is probably real (he gives it a 50% chance of being real), also asks his readers to:
Recall that the ATLAS diphoton graph also shows an excess near 1.6TeV, close to two times 750GeV, and 375GeV is just a bit higher than twice the top quark mass, 173GeV.I'm not as impressed with "almost" twice the mass, particularly when the 750 GeV v. 375 GeV pairing seems to be exact (although he also points to a possible 340 GeV mass for the lower bump). Twice the top quark mass is about 346 GeV, and twice that is about 692 GeV which is pretty much impossible to reconcile with 750 GeV unless you have a composite particle with some a lot of strong force binding energy to make toponium and very little to go further and make a toponium molecule or top tetraquark at 750 GeV that in turn almost instantly annihilates into photons.
But, of course, if you had a top quark-top antiquark composite particle, you ought to be seeing decays predominantly to pairs of b quarks and not to photons and Z bosons the way you do when pairs to top quarks that aren't bound to each other in hadrons are product. To get those decays you'd need toponium to experience a matter-antimatter annihilation to photons before the constituent top quarks could experience weak force decay. And, you'd probably want a process that produces the toponium from extremely high energy gluon fusion or something like that. (Glueball annihilation is also naively attractive, but the predicted glue ball masses aren't anywhere near a 750 GeV resonance; they're much too light.)
The diphoton channel at that energy level doesn't have a lot of potential background noise, so even a pretty modest number of diphoton detections at that energy scale could be significant.
But, there are hundreds of papers, rather than just a few leading ones, because a resonance at this mass, with the characteristics it has and the lack of strong signals in other channels at the same energy level, is not very well motivated in any of the leading extension of the Standard Model of particle physics. Also, the different data sets used to infer its existence are in some tension with each other.
For the most part, models that can accommodate a particle that decays to a 750 GeV diphoton resonance while having few other decay modes, require the existence of whole classes of other new particles to go with it (even if it is composite, rather than fundamental). This gives rise to a very baroque new beyond the Standard Model theory.
For that reason, despite the notability of the bump statistically, my money is on this turning out to be a statistical fluke or systemic experimental error, rather than an actual new particle.
We'll learn if this prediction is right or not within a year or two, depending on how many more weasel, baguettes and other mishaps interfere with the LHC experimental schedule.
Did Human Female Pelvis Evolution Create Another Biological Clock?
The obstetrical dilemma hypothesis states that the human female pelvis represents a compromise between designs most suitable for childbirth and bipedal locomotion, respectively. This hypothesis has been challenged recently on biomechanical, metabolic, and biocultural grounds. Here we provide evidence for the pelvis’ developmental adaptation to the problem of birthing large-headed/large-bodied babies.
We show that the female pelvis reaches its obstetrically most adequate morphology around the time of maximum fertility but later reverts to a mode of development similar to that of males, which significantly reduces the dimensions of the birth canal. These developmental changes are likely mediated by hormonal changes during puberty and menopause, indicating “on-demand” adjustment of pelvic shape to the needs of childbirth.Via John Hawks.
Everyone know that women can only have children from puberty to menopause, and most people who have lived in the social world of college students know that female fertility declines markedly with age before menopause. All of this, however, is basically directly hormonal and biochemical, not mechanical and morphological according to hormonal cues.
The new paper suggests that shifts in women's hips over their life cycle provides an independent biological clock that influences fertility and provides a biological bias towards having children in your 20s, rather than your 30s or later. Of course, medically safe C-sections can now bypass the limits of the birth canal on safe births later in life. But, this study ought to give pause to women who think that vaginal births for mothers of advanced maternal age are desirable because they are more "natural."
The issue of large-headed/large-bodies babies is a big one because many evolutionary anthropologists see large headed babies as a critical piece of evolution that has facilitated higher IQ in modern humans than in other primates. And, it is widely accepted that higher IQ is a key factor in modern human selective fitness.
Given the ongoing relevance of IQ and the existence of safe C-sections, is it conceivable that we could evolve to a state where safe vaginal births are no longer possible because selection for high IQ leads to selection for large headed babies and hip size is not longer a meaningful constraint on that tendency?
This paper is also a welcome reminder that genetically driven phenotypes are not necessarily an all or nothing thing. People's bodies change over their lifespans and our genes are clever enough to adapt one way at one age and another at a later age for maximum selective fitness.
Tuesday, May 3, 2016
Planet Nine Lacks A Good Origin Story
While a variety of investigators have been hot on the trail of determine where Planet Nine might be and what characteristics it might have, all of the origin stories for it are low probability ones.
Dilution Or Selection?
A new paper from Nature focuses on 51 ancient genomes from the Upper Paleolithic.
One notable observation is that Neanderthal admixture falls from 3%-6% in the early Upper Paleolithic to current levels of about 2%. This is attributed to selection, although dilution with less admixed populations could produce the same top line result. (Oase1 is an outlier at 10% from 40kya).
The paper's analysis suggests also that most Neanderthal admixture is quite old (long before cohabitation of Europe) and decayed slowly and steadily through slight natural selection, presumably in West Asia or SW Asia, rather than Europe. Indeed, the model is consistent with zero admixture of modern humans and Neanderthals in Europe itself.
Eurogenes captures many observations from the comments.
Broad brush, modern populations are really only in continuity with historic populations in Europe back to the Epipaleolithic era ca. 14,000 years ago when Europe's population was replaced following the Last Glacial Maximum when the Western Hunter Gatherer (WGH) autosomal population starts to gel. Earlier individuals loosely cluster around MA1 from 24,000 years ago with one individual from ca. 19,000 years ago looking like a transitional figure.
This is one Epipaleolithic individual from Northern Italy ca. 14,000 year ago with Y-DNA R1b. There are stronger Asia affinities in European individuals than would be expected for most of the Upper Paleolithic.
The picture form uniparental ancient DNA until now has been one of a very narrow, homogeneous gene pool with a small effective population size. To the extent that this is true, it is a post-LGM phenomena as the ancient autosomal DNA over the tens of thousands of years and thousands of miles spanned by the sample shows only fairly loose affinity.
Two out of 21 pre-LGM samples are mtDNA-M (now found almost exclusively in East Eurasia). Of 13 pre-LGM Y-DNA samples, three of C (now found almost exclusively in East Eurasia) and four are haplogroups that precede the East-West divide in Y-DNA haplogroups.
One notable observation is that Neanderthal admixture falls from 3%-6% in the early Upper Paleolithic to current levels of about 2%. This is attributed to selection, although dilution with less admixed populations could produce the same top line result. (Oase1 is an outlier at 10% from 40kya).
The paper's analysis suggests also that most Neanderthal admixture is quite old (long before cohabitation of Europe) and decayed slowly and steadily through slight natural selection, presumably in West Asia or SW Asia, rather than Europe. Indeed, the model is consistent with zero admixture of modern humans and Neanderthals in Europe itself.
Eurogenes captures many observations from the comments.
Broad brush, modern populations are really only in continuity with historic populations in Europe back to the Epipaleolithic era ca. 14,000 years ago when Europe's population was replaced following the Last Glacial Maximum when the Western Hunter Gatherer (WGH) autosomal population starts to gel. Earlier individuals loosely cluster around MA1 from 24,000 years ago with one individual from ca. 19,000 years ago looking like a transitional figure.
This is one Epipaleolithic individual from Northern Italy ca. 14,000 year ago with Y-DNA R1b. There are stronger Asia affinities in European individuals than would be expected for most of the Upper Paleolithic.
The picture form uniparental ancient DNA until now has been one of a very narrow, homogeneous gene pool with a small effective population size. To the extent that this is true, it is a post-LGM phenomena as the ancient autosomal DNA over the tens of thousands of years and thousands of miles spanned by the sample shows only fairly loose affinity.
Two out of 21 pre-LGM samples are mtDNA-M (now found almost exclusively in East Eurasia). Of 13 pre-LGM Y-DNA samples, three of C (now found almost exclusively in East Eurasia) and four are haplogroups that precede the East-West divide in Y-DNA haplogroups.