Wednesday, March 20, 2019

Anatolian Farmers Emerged From Local Hunter-Gatherers

This is completely consistent with the paradigm, but paradigm confirming research has its place too. 

The nuances are also notable. Mesolithic Europeans arose from populations that overlapped with those of the first farmers of the Fertile Crescent. And, in Anatolia, at least, Iranian/Caucasian first farmers predated Levantine first farmers.

Anatolia was home to some of the earliest farming communities. It has been long debated whether a migration of farming groups introduced agriculture to central Anatolia. Here, we report the first genome-wide data from a 15,000 year-old Anatolian hunter-gatherer and from seven Anatolian and Levantine early farmers. We find high genetic continuity between the hunter-gatherer and early farmers of Anatolia and detect two distinct incoming ancestries: an early Iranian/Caucasus related one and a later one linked to the ancient Levant. Finally, we observe a genetic link between southern Europe and the Near East predating 15,000 years ago that extends to central Europe during the post-last-glacial maximum period. Our results suggest a limited role of human migration in the emergence of agriculture in central Anatolia.
Michal Feldman, et al., "Late Pleistocene human genome suggests a local origin for the first farmers of central Anatolia." Nature Communications, 2019 DOI: 10.1038/s41467-019-09209-7

Tuesday, March 19, 2019

Progress In Estimating Hadron Masses

The scalar and axial-vector meson results are particularly an improvement over past work. Top quarks, of course, do not hadronize, so five valence quark types is appropriate. It is also worth noting that the fundamental parameters of QCD are only known to about 0.5% to 1% significance (or worse), so given the multiple parameters at issue, the 2.4%-2.9% errors are not much different from doing first principles calculations using these fundamental parameters.
Using a confining, symmetry-preserving regularisation of a vector×vector contact interaction, we compute the spectra of ground-state pseudoscalar and vector (fg¯) mesons, scalar and axial-vector (fg) diquarks, and JP=1/2+,3/2+ (fgh) baryons, where f,g,h{u,d,s,c,b}. The diquark correlations are essentially dynamical and play a key role in formulating and solving the three-valence-quark baryon problems. The baryon spectrum obtained from this largely-algebraic approach reproduces the 22 known experimental masses with an accuracy of 2.9(2.4)   %. It also possesses the richness of states typical of constituent-quark models, predicting many heavy-quark baryons not yet observed. This study indicates that diquark correlations are an important component of all baryons; and owing to the dynamical character of the diquarks, it is typically the lightest allowed diquark correlation which defines the most important component of a baryon's Faddeev amplitude.
Pei-Lin Yin, Chen Chen, Gastao Krein, Craig D. Roberts, Jorge Segovia, Shu-Sheng Xu "Masses of ground-state mesons and baryons, including those with heavy quarks" (March 1, 2019).

Details results appear below the fold.

META NOTE: This is the 1600th post at this blog. 

Thursday, March 14, 2019

Ancient DNA From Iberia

We assembled genome-wide data from 271 ancient Iberians, of whom 176 are from the largely unsampled period after 2000 BCE, thereby providing a high-resolution time transect of the Iberian Peninsula. We document high genetic substructure between northwestern and southeastern hunter-gatherers before the spread of farming. We reveal sporadic contacts between Iberia and North Africa by ~2500 BCE and, by ~2000 BCE, the replacement of 40% of Iberia’s ancestry and nearly 100% of its Y-chromosomes by people with Steppe ancestry. We show that, in the Iron Age, Steppe ancestry had spread not only into Indo-European–speaking regions but also into non-Indo-European–speaking ones, and we reveal that present-day Basques are best described as a typical Iron Age population without the admixture events that later affected the rest of Iberia. Additionally, we document how, beginning at least in the Roman period, the ancestry of the peninsula was transformed by gene flow from North Africa and the eastern Mediterranean.
IƱigo Olalde, et al.,"The genomic history of the Iberian Peninsula over the past 8000 years" 363 (6423) Science 1230-1234 (March 15, 2019). DOI: 10.1126/science.aav4040

New York Times summary here. One of many notable points it makes: "Before the Roman era, the Basque had DNA that was indistinguishable from that of other Iron Age Iberians. But Roman genes did not flow into Basque Country."

The Bell Beaker people are really the only plausible source of Steppe ancestry in the pre-2000 BE period in Iberia. The Bell Beaker people may have also facilitated some of the early contacts between Iberia and North Africa as there are artifacts indicating a Bell Beaker presence in coastal Northwest Africa.

How the Basque people ended up with the language they have with the genetic makeup that they have, and the nature of the migration from the Steppe that gave rise to the Iberian Bell Beaker people (and Iberia is the first place that the Bell Beaker culture is attested), is still a mystery, as is the evidence from ancient DNA (perhaps tweaked by the data in this paper that is not highlighted) that Iberian Bell Beaker DNA was fairly distinct from non-Iberian Bell Beaker DNA (with the former more similar to Neolithic Iberian DNA and the latter more similar to Corded Ware culture DNA).

Another enduring question is whether some or all of the Bell Beaker people spoke Celtic languages, or some pre-proto-Celtic language, or some extinct branch of the Indo-European language family, or some non-Indo-European language.

The immense demographic upheaval in the British Isles and Western Europe associated with the Bell Beaker people strongly suggests that there was a language shift at the time of their arrival from what was presumably a language derived, at least remotely, from the language of the Neolithic Anatolians that was presumably spoken by the First Farmers of Europe.

But, I am among a minority of observers who are not convinced that the people of the Corded Ware civilization (who almost certainly spoke an Indo-European language or group of closely related Indo-European languages) and the Bell Beaker people may not have spoken the same language, and that the Bell Beaker people may not even have spoken an Indo-European language, despite the fact that the two populations have very similar Steppe autosomal genetic makeup.

Given the significant Steppe Y-DNA proportions in Basque men, I seek basically two plausible scenarios. 

One is that Basque men descend from an early wave of Steppe men in Iberia who integrated into their local wives' society and adopted their wives' language. In this case, Basque is probably the closest remaining language to the language of the first farmers of Europe and in particular the Cardial Pottery culture first farmers of Europe (both the LBK first farmers and the CP first farmers are basically derived from Neolithic Anatolians and probably both spoke languages related to the language of that source population).

The other is that some steppe people spoke Indo-European languages, while the proto-Bell Beaker people spoke another non-Indo-European language related to Basque. I see the fairly clean (albeit imperfect) sorting between Y-DNA R1a (and more specifically the sub-haplogroup associated with late Neolithic, early Bronze Age Indo-Europeans in Northern Europe and South Asia), and Y-DNA R1b (and more specifically the sub-haplogroup associated with the Bell Beaker people), as possible evidence of a linguistic divide between the two populations. Indeed, I would be almost certain that the Bell Beaker people spoke a different language than other Indo-Europeans, and the only question in my mind is whether the Bell Beaker people spoke a lost sister branch language of Indo-European, or a proto-Celtic language, or a non-Indo-European language.

The problem with a late Neolithic/early Bronze Age source for the Celtic languages (when there was a likely language shift driven by Bell Beaker people whose geographic range is a decent fit to the historical geographic range of the Celtic language speaking peoples) is that the Celtic language family seems too have member languages too similar too each other to have that kind of time depth, and the strong association of culturally distinctive Celtic material culture with the very late Bronze Age/early Iron Age Urnfield and La-Tene cultures that didn't obviously give rise to a major population genetic upheaval. The later date suggested by the archaeology also seems like a decent fit to the time depth of the Celtic language family (with Urnfield possibly being associated with an earlier Italo-Celtic language branch).

One possibility is that the Celtic languages are the product of a late Bronze Age/early Iron Age superstrate language that was influenced in parallel by one group of related substrate languages in Celtic areas and a different set of substrate language influences in Italic language areas. 

I haven't yet read the body text or supplemental materials and may update this post when (and if) I do.

Friday, March 1, 2019

LambdaCDM At Odds With Cluster Data

The galaxy cluster mass scale and its impact on cosmological constraints from the cluster population

The total mass of a galaxy cluster is one of its most fundamental properties. Together with the redshift, the mass links observation and theory, allowing us to use the cluster population to test models of structure formation and to constrain cosmological parameters. Building on the rich heritage from X-ray surveys, new results from Sunyaev-Zeldovich and optical surveys have stimulated a resurgence of interest in cluster cosmology. These studies have generally found fewer clusters than predicted by the baseline Planck LCDM model, prompting a renewed effort on the part of the community to obtain a definitive measure of the true cluster mass scale. Here we review recent progress on this front. Our theoretical understanding continues to advance, with numerical simulations being the cornerstone of this effort. On the observational side, new, sophisticated techniques are being deployed in individual mass measurements and to account for selection biases in cluster surveys. We summarise the state of the art in cluster mass estimation methods and the systematic uncertainties and biases inherent in each approach, which are now well identified and understood, and explore how current uncertainties propagate into the cosmological parameter analysis. We discuss the prospects for improvements to the measurement of the mass scale using upcoming multi-wavelength data, and the future use of the cluster population as a cosmological probe.
Comments:arXiv version of review article to appear in Space Science Reviews; 44 pages, 22 figures
Subjects:Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Cite as:arXiv:1902.10837 [astro-ph.CO]
 (or arXiv:1902.10837v1 [astro-ph.CO] for this version)

Thursday, February 28, 2019

The Truth About Calculus

Alt Text: "Symbolic Integration" is when you theatrically go through the motions of finding integrals, but the actual result you get doesn't matter because it's purely symbolic."

("Symbolic integration" actually means solving an integral analytically in a general indefinite integral form, rather than numerically.)
A procedure called the Risch algorithm exists which is capable of determining whether the integral of an elementary function (function built from a finite number of exponentials, logarithms, constants, and nth roots through composition and combinations using the four elementary operations) is elementary and returning it if it is. In its original form, Risch algorithm was not suitable for a direct implementation, and its complete implementation took a long time. It was first implemented in Reduce in the case of purely transcendental functions; the case of purely algebraic functions was solved and implemented in Reduce by James H. Davenport; the general case was solved and implemented in Axiom by Manuel Bronstein. 
However, the Risch algorithm applies only to indefinite integrals and most of the integrals of interest to physicists, theoretical chemists and engineers, are definite integrals often related to Laplace transforms, Fourier transforms and Mellin transforms. Lacking of a general algorithm, the developers of computer algebra systems, have implemented heuristics based on pattern-matching and the exploitation of special functions, in particular the incomplete gamma function.[1] Although this approach is heuristic rather than algorithmic, it is nonetheless an effective method for solving many definite integrals encountered by practical engineering applications. Earlier systems such as Macsyma had a few definite integrals related to special functions within a look-up table. However this particular method, involving differentiation of special functions with respect to its parameters, variable transformation, pattern matching and other manipulations, was pioneered by developers of the Maple[2] system then later emulated by Mathematica, Axiom, MuPAD and other systems.
The fact that a function in calculus and its inverse are profoundly different in difficulty is very non-intuitive but is definitely true. The assumption that they should be similar in difficulty is similar to the faulty reasoning behind "naturalness" as a hypothesis generator and evaluator in physics.

The "alt text" while seemingly just tongue in cheek word play actually hints at a deeper truth as well. While "symbolic integration" doesn't mean what the alt text says that it does, it isn't actually uncommon in theoretical physics to have a paper that calculates something as a proof of concept or a demonstration of a method when the actual result of the calculation doesn't matter.

FYI: This blog is currently one post short of its 3% humor quota.

Tuesday, February 26, 2019

Sean Carroll On Cosmology

  1. The Big Bang model is simply the idea that our universe expanded and cooled from a hot, dense, earlier state. We have overwhelming evidence that it is true.
  2. The Big Bang event is not a point in space, but a moment in time: a singularity of infinite density and curvature. It is completely hypothetical, and probably not even strictly true. (It’s a classical prediction, ignoring quantum mechanics.)
  3. People sometimes also use “the Big Bang” as shorthand for “the hot, dense state approximately 14 billion years ago.” I do that all the time. That’s fine, as long as it’s clear what you’re referring to.
  4. The Big Bang might have been the beginning of the universe. Or it might not have been; there could have been space and time before the Big Bang. We don’t really know.
  5. Even if the BB was the beginning, the universe didn’t “pop into existence.” You can’t “pop” before time itself exists. It’s better to simply say “the Big Bang was the first moment of time.” (If it was, which we don’t know for sure.)
  6. The Borde-Guth-Vilenkin theorem says that, under some assumptions, spacetime had a singularity in the past. But it only refers to classical spacetime, so says nothing definitive about the real world.
  7. The universe did not come into existence “because the quantum vacuum is unstable.” It’s not clear that this particular “Why?” question has any answer, but that’s not it.
  8. If the universe did have an earliest moment, it doesn’t violate conservation of energy. When you take gravity into account, the total energy of any closed universe is exactly zero.
  9. The energy of non-gravitational “stuff” (particles, fields, etc.) is not conserved as the universe expands. You can try to balance the books by including gravity, but it’s not straightforward.
  10. The universe isn’t expanding “into” anything, as far as we know. General relativity describes the intrinsic geometry of spacetime, which can get bigger without anything outside.
  11. Inflation, the idea that the universe underwent super-accelerated expansion at early times, may or may not be correct; we don’t know. I’d give it a 50% chance, lower than many cosmologists but higher than some.
  12. The early universe had a low entropy. It looks like a thermal gas, but that’s only high-entropy if we ignore gravity. A truly high-entropy Big Bang would have been extremely lumpy, not smooth.
  13. Dark matter exists. Anisotropies in the cosmic microwave background establish beyond reasonable doubt the existence of a gravitational pull in a direction other than where ordinary matter is located.
  14. We haven’t directly detected dark matter yet, but most of our efforts have been focused on Weakly Interacting Massive Particles. There are many other candidates we don’t yet have the technology to look for. Patience.
  15. Dark energy may not exist; it’s conceivable that the acceleration of the universe is caused by modified gravity instead. But the dark-energy idea is simpler and a more natural fit to the data.
  16. Dark energy is not a new force; it’s a new substance. The force causing the universe to accelerate is gravity.
  17. We have a perfectly good, and likely correct, idea of what dark energy might be: vacuum energy, a.k.a. the cosmological constant. An energy inherent in space itself. But we’re not sure.
  18. We don’t know why the vacuum energy is much smaller than naive estimates would predict. That’s a real puzzle.
  19. Neither dark matter nor dark energy are anything like the nineteenth-century idea of the aether.
From Sean Carroll's blog (a January 12, 2019 post).

He is mostly, but not entirely, correct. I have put what I agree with in bold, and what I think is wrong or overstated in strikeout, and that visually makes clear the extent to which I do and do not agree with his 19 statements about cosmology.

I agree with 1-12, 14, and 18.

I disagree with 13 ("Dark matter exists. Anisotropies in the cosmic microwave background establish beyond reasonable doubt the existence of a gravitational pull in a direction other than where ordinary matter is located."). Dark matter phenomena definitely exist and require "new physics" to explain, but the interpretation he gives to the CMB is more model dependent than he acknowledges. There are, however, at most, 50-50 odds that it is caused by dark matter particles rather than gravity modification or something similar. Also, many of the more viable dark matter particle theories require a fifth force or gravity modification in addition to dark matter particles. Personally, I think that an explanation predominantly from gravity modification (including subtle refinements of GR in either a classical or quantum gravity mode) is more likely than not to be correct.

The first sentence of 15 ("Dark energy may not exist; it’s conceivable that the acceleration of the universe is caused by modified gravity instead.") is true. The second ("But the dark-energy idea is simpler and a more natural fit to the data.") is not. 

I disagree with 16 ("Dark energy is not a new force; it’s a new substance. The force causing the universe to accelerate is gravity."). This is a possibility, but not anything approaching a certainty. Indeed 16 is internally inconsistent with 15.

The last sentence of 17 ("But we’re not sure.") is true. The first two sentences of 17 ("We have a perfectly good, and likely correct, idea of what dark energy might be: vacuum energy, a.k.a. the cosmological constant. An energy inherent in space itself.") are mostly true except for the "likely correct" part.

19 is mostly true, but "anything like" in 19 is susceptible to different interpretations and if you standard for similarity is low, it isn't true, so it slightly overstates this proposition. 

Monday, February 25, 2019

The NYT On Dark Energy

Today's New York Times has an article discussing recent research efforts related to the phenomena attributed to dark energy.

Two basic kinds of astronomy observations, the first being discrepancies on the order of 9% in different kinds of measurements of Hubble's constant which measures the rate at which the expansion of the universe seems to be accelerating, and the other involving discrepancies in the apparent rate of expansion over time from a constant value based upon myriad observations of very old quasars.

Both of these results could be due to systemic errors in astronomy measurements which are hard to quantify, or could be solved by new physics such as quintessence or phantom energy theories in which the amount of dark energy is not constant (as it is if the cosmological constant is merely added to the equations of general relativity, the leading and most simple explanation for what is observed).

The problem with the new physics approaches discussed in the article, is that the kinds of new physics that would be necessary to reproduce what the observational evidence seems to show is very weird and ill motivated. Even the proponents of these new physics explanations justify them more as a proof of concept, showing that it is possible to come up with some sort of new physics that could explain the data, rather than strongly arguing that their crazy mechanism are actually what is causing the observational discrepancies that we see.

I don't rule out the possibility of new physics in this area that will help explain the data either, although at least some of the discrepancies are almost surely due to systemic errors in astronomy observations that aren't well quantified. But, if there is a new physics solution, it seems very unlikely that the ones proposed (such as a 100,000 year period in the early universe where extra dark energy appears for a while and then vanishes, or a theory in which energy is not conserved when things go fast enough) are actually the right ones.

Negative Mass Models Of Dark Energy And Dark Matter Don't Work

Another explanation of dark energy and dark matter fails miserably.

Can a negative-mass cosmology explain dark matter and dark energy?

A recent work by Farnes (2018) proposed an alternative cosmological model in which both dark matter and dark energy are replaced with a single fluid of negative mass. This paper presents a critical review of that model. A number of problems and discrepancies with observations are identified. For instance, the predicted shape and density of galactic dark matter halos are incorrect. Also, halos would need to be less massive than the baryonic component or they would become gravitationally unstable. Perhaps the most challenging problem in this theory is the presence of a large-scale version of the `runaway' effect, which would result in all galaxies moving in random directions at nearly the speed of light. Other more general issues regarding negative mass in general relativity are discussed, such as the possibility of time-travel paradoxes.
Comments:Submitted to A&A
Subjects:Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)
Cite as:arXiv:1902.08287 [astro-ph.CO]
(or arXiv:1902.08287v1 [astro-ph.CO] for this version)
Certain classes of modified gravity theories are also ruled out by new observations:

Constraints of general screened modified gravities from comprehensive analysis of binary pulsars

Testing gravity by binary pulsars nowadays becomes a key issue. Screened modified gravity is a kind of scalar-tensor theory with screening mechanism in order to satisfy the tight Solar System tests. In this paper, we investigate how the screening mechanism affects the orbital dynamics of binary pulsars, and calculate in detail the five post-Keplerian (PK) parameters in this theory. These parameters differ from those of general relativity (GR), and the differences are quantified by the scalar charges, which lead to the dipole radiation in this theory. We combine the observables of PK parameters for the ten binary pulsars, respectively, to place the constraints on the scalar charges and possible deviations from GR. The dipole radiation in the neutron star (NS) - white dwarf (WD) binaries leads to more stringent constraints on deviations from GR. The most constraining systems for the scalar charges of NS and WD are PSR~B1913+16 and PSR~J1738+0333, respectively. The results of all tests exclude significant strong-field deviations and show good agreement with GR.
Comments:14 pages, 20 figures, 2 tables, ApJ accepted
Subjects:General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)
Cite as:arXiv:1902.08374 [gr-qc]
(or arXiv:1902.08374v1 [gr-qc] for this version)
Also, LIGO rules out certain kinds of compact dark matter objects in the solar system:

Gravitational waves from compact dark matter objects in the solar system

Dark matter could be composed of compact dark objects (CDOs). We find that a close binary of CDOs orbiting {\it inside} solar system bodies can be a loud source of gravitational waves (GWs) for the LIGO and VIRGO detectors. An initial search of data from the first Advanced LIGO observing run (O1), sensitive to h01024, rules out close binaries orbiting near the center of the Sun with GW frequencies (twice the orbital frequency) between 50 and 550 Hz and CDO masses above approximately 10^{-9} M_sun.
Comments:5 pages, 3 figures
Subjects:General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as:arXiv:1902.08273 [gr-qc]
(or arXiv:1902.08273v1 [gr-qc] for this version)
On the other hand, this new gravity based paper looks interesting:

Dark matter effect attributed to the inherent structure of cosmic space

We propose that anomalous gravitational effects currently attributed to dark matter can alternatively be explained as a manifestation of the inherent structure of space at galactic length scales. Specifically, we show that the inherent curvature of space amplifies the gravity of ordinary matter such that the effect resembles the presence of the hypothetical hidden mass. Our study is conducted in the context of weak gravity, nearly static conditions, and spherically symmetric configuration, and leverages the Cosmic Fabric model of space developed by Tenev and Horstemeyer [T. G. Tenev and M. F. Horstemeyer, Int. J. Mod. Phys. D 27 (2018) 1850083; T. G. Tenev and M. F. Horstemeyer, Rep. Adv. Phys. Sci. 2 (2018) 1850011]
Subjects:General Relativity and Quantum Cosmology (gr-qc)
MSC classes:83D05, 74L99
Journal reference:International Journal of Modern Physics D (2019) 1950082
Cite as:arXiv:1902.08504 [gr-qc]
(or arXiv:1902.08504v1 [gr-qc] for this version)

This is summed up in the preprint's conclusion:
We showed that the inherent curvature of physical space (that is curvature uncaused by matter) amplifies the gravitational effects of ordinary matter and produces the kind of gravitational anomalies that are currently attributed to the presence of dark matter (DM). We proposed the Inherent Structure Hypothesis (ISH) stating that the so called DM effect is the manifestation of the inherent structure of space at galactic length-scales, and not the result of invisible mass. 
We demonstrated that any DM effect, which can be explained by the Modified Newtonian Dynamics (MOND) theory or by the presence of a DM halo, can be equally well explained by the ISH. At the same time, we showed, ISH allows for DM effects that cannot be explained by MOND or by DM halos. Therefore, we concluded that the Inherent Structure and DM explanations are observationally equivalent with each other to within some distance from the center of a gravitating system. However, beyond such distance, the ISH predicts that the gravitational impact of the hypothetical dark matter begins to be reversed and is nearly completely eliminated at sufficiently far distances. This is a verifiable prediction that would distinguish our model from other explanations of the DM effect. 
In the comparison between the ISH and MOND we noted an interesting relationship between the size of a gravitational system and its Schwartzchild radius through the MOND parameter a0. Such relationship hinted at the structural underpinnings of the DM effect. 
The Inherent Structure Hypothesis stems from the principle that structure is a fundamental aspect of matter, space, and nature in general, and as such can be incorporated into cosmological models that subscribe to the same principle.