Tuesday, May 28, 2013

130 GeV Fermi Line Inconsistent With Dark Matter

Whatever the Fermi line is, it isn't a dark matter signal
The cusp in the dark matter distribution required to explain the recently found excess in the gamma-ray spectrum at energies of 130 GeV in terms of the dark matter annihilations cannot survive the tidal forces if it is offset by 1.5° from the Galactic center as suggested by observations.
From Dmitry Gorbunov, Peter Tinjakov, "On the offset of a DM Cusp and the interpretation of the 130 GeV line as a DM signal" via Tommasso Dorigo's blog.

One of the strongest bits of experimental data favoring WIMP (weakly interacting massive particle) dark matter with particle masses at the electroweak scale is the Fermi line, i.e. 130 GeV photon signals detected by the Fermi Gamma-Ray Space Telescope that have no understood astronomical process as its source.

These signals have been hypothesized by theorists to be evidence of the annihilation of matter and antimatter dark matter particles of about 130 GeV mass with each other. But, even if these signals are evidence of such annihilations, they can only be the dark matter that everyone is looking for as the biggest gap in fundamental physics today if the signals come mostly from the right direction. The latest study indicates that they do not. Thus, the Fermi line grows an ever lengthening list of possible direct detections of dark matter or dark matter annihilation signals that have been ruled out as true dark matter signals.

The Fermi line could still be real; it just can't be dark matter

The study still doesn't tell us if the Fermi line is "real" or just some sort of statistical or systematic error in the observations.  So far, no plausible explanation that could explain the Fermi line as an experimental error has been identified. 

But, for example, suppose there was a supersymmetric particle with that mass or a second kind of Higgs boson of slightly different mass than the one already discovered, that was highly unstable.  If this particle existed, its annihilation could produce this signal in some unknown process, such as some kind of high energy interactions near the Milky Way's central black hole's event horizon, even though such an unstable particle can't be an important source of the phenomena attributed to dark matter.

A true SUSY optimist could see both the Fermi line and the ASM-02 positron excess as signatures of SUSY particle annihilations.  But, even for a SUSY optimist, the likelihood that a canonical sparticle or SUSY Higgs boson can provide a dark matter candidate that fits the experimental evidence is rapidly waning. 

The best hope in a SUSY theory for a dark matter candidate is now the same as it is in minimal Standard Model extensions - some sort of sterile (i.e. right handed) neutrino with a mass on the other of 2 keV (i.e. warm dark matter).  These models are highly constrained and it hasn't been fully established that they can really reproduce all observed dark matter phenomena.  But, these particles are the only game in town using the dark matter particle paradigm that hasn't been pretty definitively ruled out by observational evidence to date.

Independent lines of experimental evidence disfavor WIMP dark matter

This isn't too surprising. 

Multiple lines of evidence disfavor weakly interacting dark matter particles with masses of 10 GeV or so or more.  For example, heavy WIMPs are disfavored by (1) the small scale structure of the universe (i.e. the fact that there aren't enough dwarf satellite galaxies), (2) the exclusion ranges in multiple direct dark matter detection experiments at cross-sections of interactions many orders of magnitude weaker than those of neutrinos, (3) the "cuspy halo" problem (that heavy wimp dark matter doesn't naturally distribute itself in the shapes necessary to match observed galactic rotation curves), and (4) the non-detection of particles in the appropriate mass ranges at particle accelerators like the LHC. 

A determination that the directional source of the Fermi line gamma-rays is inconsistent with dark matter just adds one more independent line of experimental data to the others.

While the refutation of the ASM-02 positron excess as a possible dark matter annihilation signal at 300 GeV or more isn't yet complete, the astronomy data problems with cold dark matter apply to particles this heavy with especially great force, and there is other circumstantial evidence (such as the fact that other things we would expect to discovery at the same time as the annihilation of a dark matter particle that heavy) have not been seen.  Cosmic rays from quasars continue to be a more plausible source for this signal.

A personal conjecture

For what it is worth, my own intuition, informed by studies that disfavor dark matter models with more than one kind of dark matter particle in any significant frequency, is that a warm dark matter sterile neutrino, if there is one, is not a right handed neutrino in the usual sense, but is instead a singlet particle that is taxonomically part of the gravity sector in a gravi-weak unification theory or some other particle outside the domain of the three Standard Model forces and their interactions, rather than a missing piece within the SU(3)*SU(2)*U(1) group structure of the Standard Model that has almost nothing to do with any Standard Model particle other than the Higgs boson (which might interact with dark matter since it seems to couple to mass).

Also, while warm dark matter is the best prospect in the dark matter paradigm, I believe that it is still hasty to rule out theories outside that paradigm.  The best runner up would be some sort of gravity modification, possibly rooted in quantum gravity effects or limitations on the wavelengths of gravity waves as a result of the finite size of the universe.  Another would be that the phenomena attributed to dark matter actually consist, at least in part, of multiple kinds of "dim matter" phenomena consisting of ordinary matter, quite possibly maintained in some sort of dynamic equilibrium by ill understood astronomy processes, particularly in galactic clusters and/or galaxy formation, about which we have the least solid understanding.

Thursday, May 16, 2013

How Long Was A Trip From Sweden To Cyprus And Back By Sail?

As noted in the previous post at this blog, there appears to have been maritime trade network that extended from Southern Sweden to Cyprus in the Bronze Age (ca. 1500 BCE and later).

How long would it have taken to sail the entire distance and back?

Resort to an atlas (giving the benefit of the doubt to the ability of ancient sailors to take straight oversea routes rather than hugging the coast), shows that the total distance by sea is about 4000 nautical miles one way, and hence an 8000 nautical mile long round trip.

Based upon historically attested reports of travel times by sail in the Roman era, sailing speeds averaged about four knots with favorable winds and about two knots with unfavorable winds. 

Canny pre-modern sailors probably knew the wind patterns well enough to time their trips so that they had favorable winds at least half of the time, suggesting an average speed of at least three knots over such a long, multistage journey.

This would suggest a one way travel time of about 56 days of travel time, and a round trip travel time of about 112 days. 

But, while the trips used to calibrate these speeds in the Mediterranean may have been mostly direct trips, for a trip of this distance, probably at least two days a week and possibly more to conduct the trade that was the point of these cruises, would have been spent in port. 

This gives us our answer (below the jump):

Tuesday, May 14, 2013

Bronze Age Long Distance Trade In Europe

Dienekes' Anthropology blog notes three papers showing imports of early Nordic Bronze Age metals from as far as Cyprus, in exchange for amber making its way as far as the Mycenaean Greeks. 

Maju, in turn, gives these papers a more critical analysis looking at them in a wider archaeological context in light of additional data points.  He emphasizes the likely intermediate role played by Iberians in these long trade connections (perhaps as the hub with the Scandinavian and Eastern Mediterranean connections as the ends of spokes of the network).  He notes the problems with a chronology that gives the Nordic Bronze Age a Mycenaean source (the Nordic Bronze age begins two hundred years before the Nordic Bronze Age and this part of the link is thinner than the abstracts to the papers would suggest). 

Maju also tempers the implications of the papers suggesting that the Minoans did not engage in East-West trade in the Mediterranean and that this connections was made for the first time by the Mycenaeans, even though it does appear that the Minoans may not have been part of the Eastern Mediterrean-Iberian bronze for Nordic amber trade route that these papers have documented.  He also makes the useful observation that any trade in copper must also have involved trade in tin when the end products traded were bronze artifacts and that the papers are silent about the source of the tin in these artifacts even though they do identify the sources of the copper.

Also, Maju notes the spread culture specific symbols (in particular four interlocking spirals) of not entirely certain cultural origins in this network.  This provide a parallel line of evidence to explain the connections that helps to discriminate between alternative theories concerning the nature of the trade links joining the end points of the Southern Sweden to Greece and Cyprus.  He also notes that important timing of the appearance of Greek cultural influences in Iberia which coincides with the earliest evidence of this pan-European Bronze Age trade network.

While Maju's analysis casts serious doubt on the naive implications of these three papers, his criticism is constructive and does a great deal to illuminate an alternative visions of the way that distant cultures in Bronze Age Europe interacted economically and via cultural contact in this era. 

A naive reading of the three papers could easily lead to my first impression which was that this link might be powerful evidence that the Indo-European Germanic language and peoples are directly derived from the Indo-European Mycenaeans.  These cultures, respectively, are the first attested Indo-European cultures in their respective geographic locations.  Prior to reading these papers, it had not been clear to me, at least, that the first half of the Nordic Bronze Age was culturally (and presumably linguistically) Germanic at all (for the second half of the Nordic Bronze Age this is much more clear).  A first read of the paper suggested, astoundingly, that the Germanic languages might actually be derived from ancient Greek.  Closer inspection, aided by Maju's analysis, has largely dismissed that theory as implausible, and muddied the waters as to whether the early Nordic Bronze Age peoples of Southern Sweden really were Indo-European at all (which is the view with which I had started).  But, these new papers do show that there really was a regular pan-European maritime trade network in existence as far back as 1500 BCE, along the Southern coast of Europe and all of the way up the Atlantic coast to the Baltic Sea.

Maju's Iberio-centric suggestion that copper and tin mines in Iberia may well have formed the principal source of metal production for this trade network and that it may have been its hub (perhaps indeed even providing a source for Plato's legendary account of "Atlantis"), in the end, provides a very credible "forest" level big picture interpretive lens that can explain all of the archaeological data without requiring any unreasonably far fetched assumptions.

In terms of questions of historical linguistics and the associates clash of great prehistoric European civilizations, Maju's read tends to suggest that the Atlantic coast and early Nordic Bronze Age may have been in a Vasconic, rather than Indo-European sphere of influence with Mediterranean influences transmitted via the Atlantic maritime trade routes mediated though the Iberian civilization of that era.  Still, these papers do provide fuel for the conjecture that Bronze Age Indo-European civilizations may have been far more conscious of the cultural counterparts at vast distances from them than had previously been safe to assume.  The world was smaller and better understood, earlier on, than we have given the residents of prehistory credit for.

Wednesday, May 8, 2013

Study Purporting To Link Seven Language Families At 15 kya Time Depth Based On Iffy Data

On the web site of the Proceedings of the National Academy of Sciences, in the "Early Edition" section, is an article by Mark Pagel, Quentin D. Atkinson, Andreea S. Calude, and Andrew Meade: "Ultraconserved words point to deep language ancestry across Eurasia". The authors claim that a set of 23 especially frequent words can be used to establish genetic relationships of languages that go way, way back — too far back for successful application of the standard historical linguistics methodology for establishing language families, the Comparative Method. The idea is that, once you've determined that these 23 words are super-stable (because they're used so often), you don't need systematic sound/meaning correspondences at all; finding resemblances among these words across several language families is enough to prove that the languages are related, descended with modification from a single parent language (a.k.a. proto-language).

From Language Log.

As the trenchant analysis in the linked post explains, the study is deeply flawed because it is based on dubious choices of cognates in the seven proto-languages which were compared. In many cases, there are several cognates for the allegedly ultraconservated word and there is no consensus on which is correct in the proto-language, but the authors simply choose one by whim.

The data also cast serious doubt on the hypothesis that these words are truly ultra-conserved. For example, only a quarter of the ultraconserved Indo-European cognates survive in English, despite a time depth from proto-Indo-European to English estimated by more reliable means on the order of 6,000 years. The survival rates of these "ultraconserved" words are even lower in some of the other language families examined.

The hypothesis that the seven families discussed in the paper are part of a single macro-language family is not widely accepted among linguists, and isn't a good fit to genetic data for the populations who speak them either, as explained in comments to this post at Dienekes' Anthropology blog.

There is lots of very good research in the area of historical linguistics, but this, like a number of other papers with Quentin D. Atkinson as one of the authors, isn't one of them.

GR Uniquely Determined By Properties Of Hypothetical Graviton

On the Origin of Gravitational Lorentz Covariance



Justin Khoury, Godfrey E. J. Miller, Andrew J. Tolley(Submitted on 3 May 2013)



We provide evidence that general relativity is the unique spatially covariant effective field theory of the transverse, traceless graviton degrees of freedom. The Lorentz covariance of general relativity, having not been assumed in our analysis, is thus plausibly interpreted as an accidental or emergent symmetry of the gravitational sector. . . . Lorentz covariance is a central pillar of the modern field-theoretic interpretation of general relativity (GR). From this point of view, GR is no more and no less than the unique Lorentz covariant theory of an interacting massless spin-2 particle. In this paper, we show that GR can be derived without assuming Lorentz covariance. Our approach relies on the weaker assumption of spatial covariance, within the context of the effective field theory of the transverse, traceless graviton degrees of freedom[.]




The massless spin-2 graviton, while hypothetical and never directly observed, has strong theoretical support for this reason. No other hypothetical particle is so widely believed to really exist.


Friday, May 3, 2013

WIMP Dark Matter Does Not Exist

For decades, the prime candidates for dark matter were WIMPs (weakly interaction massive particles), that interacted only via the weak nuclear force and gravity, and that had masses in the GeV to thousand GeV range.  Evidence from multiple experiments essentially rules out the existence of such particles as an important constituent of dark matter.

Direct searches for WIMPS have excluded the entire parameter space of WIMP dark matter candidates, and all hints of WIMP dark matter in any given experiment have been contradicted by many other independent experiments.  Astronomy data compel the conclusion that if dark matter exists, that its particles must look like 2 keV sterile neutrinos, rather than GeV scale WIMPS.  Weakly interacting and SUSY particles have been ruled out in the appropriate mass ranges.

Note also that the direct dark matter searches, by pushing down the maximum possible cross-section of interaction of any heavy WIMPS to about 10^-44 v. 10^-36 or so for neutrinos, rule out Cold Dark Matter models in which the CDM particles deviate meaningfully from being sterile and collisionless.  This makes astronomy simulation exclusions ruling out pure collisionless CDM conclusive for pretty much all kinds of CDM that couldn't be detected by Xenon-100.

Direct Searches For WIMPs have come up empty

The Xenon-100 experiment is the most sensitive of all of the direct dark matter detection experiments that has reported results. Xenon-100 contradicts all positive results for direct dark matter detection.

Its results from 2012 ruled out the existence of dark matter particles with the properties purportedly seen in five other experiments, only a couple of which are consistent with each other (as well as those associated with Fermi line (ca. 130 GeV) and AMS-02 experiment (of at least 350 GeV) that are looking for evidence of dark matter-antimatter annihilation).

For comparison purposes, the cross-sections of WIMP-Nucleon interaction probed are many orders of magnitude weaker than neutrino-nucleon cross-sections of interaction over almost all of the region excluded.


 





As Lubos Motl notes:

You see various claims of this kind – not really compatible with each other – made by DAMA/I, DAMA/Na, CoGeNT, CRESST-II. An extra shape could perhaps be added to reflect the data from PAMELA, Fermi, and the newest three events from CDMS II (which wouldn't be too far from the CoGeNT potato).

On the other hand, the long lines depict the statements by the "negative experiments" that claim that all the points above their curve are excluded: SIMPLE, COUPP, ZEPLIN-III, EDELWEISS, CDMS (2010/2011: later betrayed the axis), and – most famously – XENON100. I say "most famously" because XENON100 is by far the most powerful experiment of this kind, at least among the negative ones.

The newest exclusion curve makes this priority even more obvious. Note the blue line inside the green-and-yellow (Brazil) band at the bottom (the exclusion is about a sigma stronger than expected). It is safely below all the "positive" potato ellipses and it is also well below the other exclusion curves. The contradiction between the latest XENON100 results and the "positive" experiments couldn't be stronger. Well, it could but it's already strong enough! ;-) One may say that pretty much all the preferred regions are disfavored by XENON100 at 5 sigma or more.

Note that the liquid xenon is a relatively diverse mixture of many isotopes (or do they filter which ones they use?). So the absence of signals is probably not due to some special properties of a xenon nucleus. On the other hand, the absence could be explained if the signals ultimately involved the interaction of a particle with the electrons – because xenon (unlike germanium, silicon, and all the other elements used in the experiments) is an inert gas with full electron shells and L=S=J=0 , when it comes to atomic physics. The events don't look like interactions with the electrons but there could be some subtleties. The tension between XENON100 and others seems so strong that the inert character of xenon seems "almost necessary" for me to understand the apparent xenophobia of the dark matter particle – but the de Broglie wavelength of the new particle would have to be of atomic size or longer for the vanishing atomic angular momentum to matter at all (which seems like an insanely low momentum, too). Also note that the collisions with the electrons are supposed to be "background" and distinguished from the dark-matter-like collisions with the nuclei but there could be a reason why some particle's collisions with the electrons look nucleus-like.
Each experiment that claims to have seen a dark matter particle with a particular cross-section of interaction and mass has about ten other experiments that have seen nothing in the same parameter space.  The case that all of the claimed direct dark matter detections reported to date are erroneous is quite powerful.  This is particularly so because the kinds of signals purportedly seen are more or less identical to the kinds of signals that would be seen if an unaccounted for source of background noise was omitted from the analysis:
Yet one more sobering fact (NYU’s Neal Weiner emphasized this in his talk last week in Princeton) is that in all of these underground experiments, a failure to account for a small background will typically show up as a few extra low-energy collision candidates, which will then closely resemble what you’d expect for a low-mass dark matter particle. In other words, lightweight dark matter is what an oops! will look like.
Efforts are currently underway to build a Xenon based sensor that is more sensitive by the same factor as the leap from Xenon-10 to Xenon-100 illustrated above.

Astronomy data rule out Cold Dark Matter models

Astronomy simulations that show galactic scale structures and halo shapes different from those that cold dark matter would produce also rule out most cold dark matter in the 1 GeV and up range, and favor warm dark matter models instead with particles closer to a single kind of 2 keV mass particle that behaves like a sterile neutrino, although the exclusions of heavier and lighter dark matter particles is more definitive than the positive evidence that a 2 keV dark matter particle (give or take) could fit the data.

A good summary of the reasons that cold dark matter is experimentally excluded can be found at H.J. de Vega and N.G. Sanchez, “Warm dark matter in the galaxies:theoretical and observational progresses. Highlights and conclusions of the chalonge meudon workshop 2011″ (14 Sept 2011) http://arxiv.org/abs/1109.3187 Here are some key quotes from the abstract and body text:

Warm Dark Matter (WDM) . . . essentially works, naturally reproducing the astronomical observations over all scales: small (galactic) and large (cosmological) scales (LambdaWDM). Evidence that Cold Dark Matter (LambdaCDM) and its proposed tailored cures do not work at small scales is staggering. . . .
The most troubling signs of the failure of the CDM paradigm have to do with the tight coupling between baryonic matter and the dynamical signatures of DM in galaxies, e.g. the Tully-Fisher relation, the stellar disc-halo conspiracy, the maximaum disc phenomenon, the MOdified Newtonian Dynamics (MOND) phenomenon, the baryonic Tully-Fisher relation, the baryonic mass discrepancy-acceleration relation, the 1-parameter dimensionality of galaxies, and the presence of both a DM and a baryonic mean surface density. . . .
It should be recalled that the connection between small scale structure features and the mass of the DM particle follows mainly from the value of the free-streaming length lfs. Structures smaller than lfs are erased by free-streaming. WDM particles with mass in the keV scale produce lfs ∼ 100 kpc while 100 GeV CDM particles produce an extremely small lfs ∼ 0.1 pc. While the keV WDM lfs ∼ 100 kpc is in nice agreement with the astronomical observations, the GeV CDM lfs is a million times smaller and produces the existence of too many small scale structures till distances of the size of the Oort’s cloud in the solar system. No structures of such type have ever been observed. Also, the name CDM precisely refers to simulations with heavy DM particles in the GeV scale. . . . The mass of the DM particle with the free-streaming length naturally enters in the initial power spectrum used in the N-body simulations and in the initial velocity. The power spectrum for large scales beyond 100 kpc is identical for WDM and CDM particles, while the WDM spectrum is naturally cut off at scales below 100 kpc, corresponding to the keV particle mass free-streaming length. In contrast, the CDM spectrum smoothly continues for smaller and smaller scales till ∼ 0.1 pc, which gives rise to the overabundance of predicted CDM structures at such scales. . . . 
Overall, seen in perspective today, the reasons why CDM does not work are simple: the heavy wimps are excessively non-relativistic (too heavy, too cold, too slow), and thus frozen, which preclude them to erase the structures below the kpc scale, while the eV particles (HDM) are excessively relativistic, too light and fast, (its free streaming length is too large), which erase all structures below the Mpc scale; in between, WDM keV particles produce the right answer. 
See also in accord: S. Tulin, et al. “Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure” (15 Feb 2013) http://arxiv.org/abs/1302.3898:
As is well known, the collisionless cold DM (CCDM) paradigm has been highly successful in accounting for large scale structure of the Universe. . . . Precision observations of dwarf galaxies show DM distributions with cores, in contrast to cusps predicted by CCDM simulations. It has also been shown that the most massive subhalos in CCDM simulations of Miky Way (MW) size halos are too dense to host the observed brightest satellites of the MW. Lastly, chemo-dynamic measurements in at least two MW dwarf galaxies show that the slopes of the DM density profiles are shallower than predicted by CCDM simulations.
A number of more recent papers have highly constrained the mass range for warm dark matter and have disfavored models with multiple kinds of dark matter.

deVega and Sanchez, for example, offer up, "Dark matter in galaxies: the dark matter particle mass is about 2 keV" (Submitted on 2 Apr 2013) http://arxiv.org/abs/1304.0759
Warm dark matter (WDM) means DM particles with mass m in the keV scale. For large scales, for structures beyond 100 kpc, WDM and CDM yield identical results which agree with observations. For intermediate scales, WDM gives the correct abundance of substructures. Inside galaxy cores, below 100 pc, N-body classical physics simulations are incorrect for WDM because at such scales quantum effects are important for WDM. Quantum calculations (Thomas-Fermi approach) provide galaxy cores, galaxy masses, velocity dispersions and density profiles in agreement with the observations. All evidences point to a dark matter particle mass around 2 keV. Baryons, which represent 16% of DM, are expected to give a correction to pure WDM results. The detection of the DM particle depends upon the particle physics model.  . . . So far, not a single valid objection arose against WDM.
See also, for example, C. Watso, et al. “Constraining Sterile Neutrino Warm Dark Matter with Chandra Observations of the Andromeda Galaxy” http://arxiv.org/abs/1111.4217 (10 Jan 2012) (WDM mass capped at 2.2 keV); R. de Souza, A. Mesinger, A. Ferrara, Z. Haiman, R. Perna, N. Yoshida, “Constraints on Warm Dark Matter models from high-redshift long gamma-ray bursts” (17 Apr 2013) http://arxiv.org/abs/1303.5060 (WMD mass at least 1.6 keV); D. Anderhaldena, et al. “Hints on the Nature of Dark Matter from the Properties of Milky Way Satellites” (12 Dec 2012) http://arxiv.org/pdf/1212.2967v1.pdf (mixed CDM/WDM models disfavored); J. ViƱas, et al. “Typical density profile for warm dark matter haloes” (9 Jul 2012) http://arxiv.org/abs/1202.2860 (models with more than one WDM species disfavored);  Xi Kang, Andrea V. Maccio, aaron A. dutton, "The effect of Warm Dark Matter on galaxy properties: constraints from the stellar mass function and the Tully-Fisher relation" (8 April 2013) http://arxiv.org/abs/1208.0008 (WDM mass of more than 0.75 keV and consistent with 2 keV).

Weakly interacting particles light enough to be dark matter are ruled out experimentally

Particles that interact via the Standard Model weak force with masses of less than 45 GeV have been excluded for many years by precision electro-weak measurements at LEP (and this will soon rise to 62.5 GeV as Higgs boson decays are analyzed).

This means that any dark matter particles must interact with ordinary matter, if it interacts at all other than via gravity, via a force other than the three Standard Model forces (although it could conceivably couple to the Higgs boson).

SUSY can't supply particles that could be dark matter

Searches for SUSY particles at colliders like the LHC have likewise established that there are no sparticles with masses below the hundreds of GeV in fairly simple MSSM and NMSSM SUSY models.

None of the SUSY models propose particles consistent with experimental data describing dark matter phenomena. Any viable explanation of dark matter effects needs to come from a source outside SUSY and SUGRA theories.

Experiments do not rule out the possibility that ephemeral and unstable heavy SUSY particles exist, but even if they do, they cannot the source of dark matter. SUSY theories, generically, have no features which could help solve this most glaring of remaining unsolved problems in fundamental physics.

Wednesday, May 1, 2013

Some Important Open Issues In Human Prehistory

1. When and where did Neanderthal admixture take place?

One, two and three admixture event scenarios are all plausible (and, of course, more complex scenarios are also possible).

The simplest model assumes that admixture took place ca. 100 kya to 75 kya at a time when the archaeology shows the two species overlapping in the Levant and the effective population size would have been smallest, and not thereafter. But, this would mean that a schism into West Eurasian and East Eurasian populations would have had to happen very early on to prevent the admixed Neanderthal genes from coming closer to fixation between the proto-West Eurasians and proto-East Eurasians than differences in which Neanderthal genes are found in each population reflect.

Another one admixture model puts the date closer to 50-75 kya when the modern human population is at a post-Toba low point after an initial Out of Africa surge, perhaps in an Arbian or Persian Gulf refugium. This reduced effective population size, and allows for a sustained period of declining population during which genetic drift can loose some of the Neanderthal inheritance and give rise to Founder effects not likely to be seen in a rapidly expanding population that has reached fixation.

In a simple two event model, West Eurasians and East Eurasians split before admixture takes place and Neanderthal admixture takes place in parallel processes that produce similar overall levels of admixture in each clade of Eurasians in different places - perhaps one in Anatolia, and another in Arabia, Persia or South Asia. This also has the virtue of driving down effective population sizes in each source population.

A three event model combines these two models, which some admixture taking place early on and pre-schism and some taking place later in parallel.

An example of a more complex model would be one with a common admixture event, additional East Eurasian admixture, and then additional West Eurasian admixture that is diluted in the Upper Paleolithic to Neolithic transition by West Asian populations that did not experience the additional West Eurasian admixture experienced by Europeans with prolonged co-existence with Neanderthals.

2. Were there cases of archaic admixture in Africa?

Preliminary population genetic analysis and possibly one Y-DNA haplogroup A00 that looks older than the species make this look plausible and may have happened in two or three separate cases there quite recently.

The case for Neanderthal and Denisovan admixture where observed is in my opinion rock solid and not adequately explained by any other mechanism (such as deep population structure in Africa within modern humans).

The window of time in which additional non-African, non-Neanderthal, non-Denisovan admixture could be discovered in modern humans alive today hasn't completely closed but is well on its way to doing so. It is quite clear that this isn't present outside modern relict populations of Eurasia and the Americas.

3. It is clear that there was a major modern human population genetic transition in Europe between the Upper Paleolithic and the early Iron Age. How much of this transition in any given part of Europe took place:
* during the Mesolithic era on the eve of the Neolithic revolution;
* when the first farmers arrived with the Neolithic revolution;
* in the mid- to late Neolithic (i.e. the Copper Age and early Bronze Age);
* in the early Iron Age.

Two subquestions here are particularly unclear.

First, were Y-DNA Haplogroup R1b and mtDNA haplogroup H, respectrively which expanded from Iberia during the Neolithic era and Bronze Age indigeneous haplogroups in continuity with the Paloelithic era, or did they arrive with folk migrations in the Mesolithic, the early Neolithic, or the Bell Beaker people?

Tenatively, I favor an arrival of R1b predominantly with the Bell Beaker people, and an arrival of mtDNA haplogroup H in Iberia mostly in the Mesolithic or with the Bell Beaker people. But, there is no ancient Y-DNA evidence old enough to definitively resolve the question, mutation rate based dates are too uncertain to resolve the issue, and the ancient mtDNA evidence is thin. Publically available data from France on this point is particularly thin.

Second, what were the relative contributions to the expansion of Y-DNA Haplogroup R1b and mtDNA haplogroup H, respectrively which expanded from Iberia during the Neolithic era and Bronze Age of the first farmer early Neolithic megalithism culture and the Bell Beaker expansion?

I suspect that R1b and H expansions in Western Europe are predominantly Bell Beaker rather than Megalithic, but the eivdence is not yet secure enough to be sure.

This goes hand in hand with the question of whether the Bell Beaker expansion gave rise to language shift from previous languages of the first farmers of that region. I suspect that it did, but resolution of this prehistoric genetic question would go a long way towards shoring up or undermining that assumption.

On the other hand, many points are fairly settled.

In my mind, there is increasingly little reason to doubt that linguistically Indo-European didn't arrive in Western Europe until at least the Urnfield culture, and that prior to that point almost the entire maximal range of Bell Beaker influence had at some point been linguistically Vasconic.

In my mind, it is all but settled that the Indo-European Iron Age tweaks to the gene pool of Western Europe were quite modest.

It is also likely all but settled in my mind that mtDNA H was at the very least confined to far Southern regions in Europe until the Neolithic at the earliest, and that mtDNA H bearers did not participate materially in the repopulation of Europe immediately after the retreat of the glaciers after the Last Glacial Maximum. This in turn implies that this was probably not an important mtDNA component of refugia populations that participated in this repopulation and were probably rare in, or absent from Southern Europe until at least the Mesolithic (e.g. as a pilot wave from the Fertile Crescent and vicinity in advance of the first farmers on the eve the Neolithic revolution).

4. What were the geographic and archaeological culture sources for the first wave Neolithic populations of Europe and the Bell Beaker peoples?

Modern Europe is to a crude approximation a composite of a West Asian, Mediterrean and Northeast Asian signal. New ancient DNA data from Central Europe makes it an unlikely Bell Beaker source population. A region roughly stretching from the Balkans to Anatolia to the Caucasus to the Zargos Mountains and Western Persia to the remainder of the Fertile Crescent are the most plausible candidates. But, some of these areas are blanks in the ancient DNA map, we don't have a perfectly solid sense of how the ancient populations of these regions differed from the modern ones other than to be forewarned that there has been a lot of historic and late prehistoric era population. It is also possible that at least one signal from a first wave Neolithic population (most likely the LBK) has been so obscured that it can no longer be distinguished from noise in modern populations.

The emerging notion of LBK as "the Neolithic revolution wave that failed" is looking more plausible.

Data from the Ukraine, Central Asia and Iran are particular thin.

5. Are the outlier dates for modern humans in the New World from 20,000 years ago and older valid or not?

There is good reason to scrutinize this data as explained in a previous post, but the evidence is what it is and if there is really no methodological flaw then we have to explain it. The possibility that outlier sites could represent archaic hominin populations that made the trip before modern humans but left a very modest footprint because their lithic technology was less advanced and they were less ecology distrupting top predators is particularly intriguing if the evidence becomes strong enough to force us to fit the theory to it.

6. What archaic hominin species is Denisovan DNA associated with?

Denisovan DNA was found in a Siberian cave. Denisovan admixture is found from roughly the Wallace line and beyond. At least two know archaic hominin species were present in between: Homo Erectus, in most of that region, and Homo Florensis on Flores and perhaps a couple of neighboring islands only. Theories about the existence as a separate species and range of Homo Heidlebergus is also sketchy.

There is no solid indication of Neanderthals beyond South Asia, but they aren't entirely ruled out, particular via a Northern route to the Denisovan cave. Some clade analysis of the Denisovan DNA suggests a clade shared with Neanderthals apart from Homo Erectus.

7. When did modern humans make it from South Asia to Southeast Asia?

The window admitted by archaeology is approximately 100,000 years ago to 45,000 years ago, with a time frame of 65,000 to 75,000 most strongly favored by the evidence, but not very conclusively established.

8. How many waves of mass migration were there to Asia in the Upper Paleolithic and when did they take place?

There is little evidence of prehistoric mass population genetic transfer between East Eurasia and West Eurasia (with a couple of notable exceptions, e.g., for Uralic populations and in the case of mtDNA haplogroup X) prior to the historic era after this initial first order split of Eurasians after leaving Africa.

The data is probably a better fit to several waves of pre-Neolithic migration, rather than just one (although the major Neolithic waves need to be understood to parse the earlier waves from the genetic data). But, the timing and paths of these waves is subject to reasonable dispute.

9. How did Homo Erectus go extinct?

While the evidence is very thin indeed on this point, extinction due to warfare and/or inability to complete for food and territory with modern humans upon first contact, outside of Flores where a cooperative mode emerged, possibly boosted by the Toba erruption or a climate shift seems most plausible.

10. When, if ever, did Homo Florensis go extinct?

The earliest possible date for the extinction is about 10,000 years ago, which is the date of the oldest skeletal evidence, but there is good reason to think that they persisted even after first contact with Europeans and that there may even be a tiny population of this species extant on one known part of one Indonensian island.

11. Is the Inuit language linguistically related to the Uralic languages as part of a transpolar language family?

There is some scholarly evidence to suggest that this might be the case, but it is not widely accepted at this point.

12. Was the Na-Dene a separate migration wave to the New World separate from the Paleo-Eskimo Dorsett, or do they represent admixture of Dorsett and first wave indigeneous American populations?

Historically, these have been treated as two separate post-first wave indigeneous population events, but some suggestive ancient DNA analysis points to collapsing them into one wave. This population is the only one strongly linked to an old world Paleo-Siberian population lingustically to date.

13. To what extent can known historical cultures of the New World in the last several thousand be properly said to be derived from each other? What is the sequence of historical cultures in North America?

There is accumulating evidence that a lot of separate archaeological cultures in the New World can all be traced back to an early one near Monroe, Louisiana.

14. What are the linguistic origins of Japanese?

The Yayoi people came from Korea and the evidence strongly favors one of the languages of Korea at about that time as a source, but there is not agreement on which one. There is likewise dispute over whether Korean and Japanese languages are related to the Altaic languages with some evidence, particularly statistical analysis of lexemes, favoring that position.

15. Is the Dravidian language family indigeneous or did it have an outside source, and if so which one?

Multiple theories exist. I tend to favor an Afro-Dravidian hypothesis with a source language not that different from early Swahili, although distinct from it. This is because the South Asian Neolithic involved a heavy component of Sahel African crops. Some archaeological evidence suggests that it could be that these crops were brought to South Asia, domesticated by the Harappans or related populations, and then returned to Africa.

16. How did Y-DNA haplogroup T end up in the western EASTERN part of South Asia?

This distribution is suggestively similar to the expansion of the Dravidian language and South Asian Neolithic. But, the resolution of the Y-DNA haplogroup T data collected so far is not high enough to discern its source (and possibly with it a source for Dravidian crop transfer).