Tuesday, January 31, 2023

The Red Deer Cave People Were Modern Humans

Ancient DNA has resolved the longstanding question of whether the Red Deer Cave People who lived in China a few thousand years before the Holocene era and seemed to have archaic skeletal features were modern humans or where archaic hominins (or archaic hominin hybrids).

The answer is that they were genetically modern humans.

I previously blogged this result here, but the linked discussion from John Hawks puts this conclusion in better context.

Thursday, January 26, 2023

Deur Takes On The Hubble Tension

Deur's analysis of the self-interaction of gravitational fields addresses the Hubble tension.
One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g., the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g., fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. 
Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution of the universe, can explain the tension. We find that with field self-interaction accounted for, both low- and high-redshift data are simultaneously well-fitted, thereby showing that gravitational self-interaction could explain the Hubble tension. Crucially, this is achieved without introducing additional parameters.
Corey Sargent, Alexandre Deur, Balsa Terzic, "Hubble Tension and Gravitational Self-Interaction" arXiv:2301.10861 (January 25, 2023).

@mitchell_porter at the Physics Forums discusses the analysis restates the argument made in the paper in summary form:
Gravitational self-interaction causes tighter binding of localized massive systems. This also leads to depletion of the gravitational field at large distances. The magnitude of gravitational depletion changes over the course of cosmic time, in a way depending on the number and type of gravitationally bound systems that have formed.

The Hubble tension can be resolved because the early universe was relatively homogeneous, so there was no gravitational depletion at high redshift; but once structure formation began, so did gravitational depletion.

A specific depletion function is proposed (equation 2, based on a 2017 paper . . .), depending on the rate and frequency of galactic mergers (parameters b and A in equation 2). The value of these parameters is inferred by fitting the depletion function to various cosmological data.

Indeed, the paper argues that the Hubble tension actually allows for a more precise determination of those parameters than Deur's previous papers that made the analysis, also allowing his previous work involving a depletion function to be more tightly fit. 

Wednesday, January 25, 2023

More Muon g-2 Calculations

It is becoming ever more clear that the BMW calculation of the Standard Model expected value of muon g-2 (which is consistent with the experimental results) is correct, while the Theory Initiative calculation of the Standard Model expected value of muon g-2 (which is in strong tension with the experimental results) is flawed.
Two preprints today with lattice calculations of a clean piece of the muon g-2 HVP (2301.08274, 2301.08696). Both blind. Both in perfect agreement with BMW and previous lattice results. Both in 3-4σ tension with the dispersive approach.

From here (hat tip to Jester).

This needs to be taken in the the context of experimental results such as those showing that there are no lepton universality violations, disfavoring sterile neutrinos, ending a CKM matrix element measurement anomaly, and myriad searches failing to find evidence of other hypothetical new particles. 

Take as a whole, these experimental results continue to ever more tightly close the door on a whole lot of proposed extensions or modifications of the Standard Model of Particle Physics.

Sunday, January 22, 2023

Modern Humans Arrived In Europe Earlier Than Previously Believed

I missed this paper when it was released. 

Discoveries at a rock-shelter in southern France put H. sapiens in Europe as early as 56,800 years ago, a new study finds. That’s around 10,000 years earlier than previously thought (SN: 5/11/20).
From Science News citing L. Slimak et al. "Modern human incursion into Neanderthal territories 54,000 years ago at Mandrin, France." Science Advances (February 9, 2022). doi: 10.1126/sciadv.abj9496.

Thursday, January 19, 2023

Progress In Measuring A Standard Model Physical Constant

Scientists at the Belle experiment have made progress in pinning down the value of a physical constant that represents the probability of a W boson mediated transition between bottom quarks and charm quarks. Bottom quarks can also transition to up quarks, and mass-energy conservation permitting, to top quarks. 

Previously, different ways of measuring this constant were producing results that weren't very close to each other given the uncertainties of the measurements.

Previous V_cb values from inclusive & exclusive decays were only marginally compatible (3σ tension). The new Vcb exclusive obtained by Belle in this work is "in agreement with inclusive determinations"
Via Twitter.

The paper is here. It also shows no lepton universality violations. The abstract of the paper is as follows:
We present a measurement of the differential shapes of exclusive B→D∗ℓν¯ℓ (B=B−,B¯0 and ℓ=e,μ) decays with hadronic tag-side reconstruction for the full Belle data set of 711fb−1 integrated luminosity. 
We extract the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameters and use an external input for the absolute branching fractions to determine the Cabibbo-Kobayashi-Maskawa matrix element and find |Vcb|CLN=(40.1±0.9)×10−3 and |Vcb|BGL=(40.6±0.9)×10−3 with the zero-recoil lattice QCD point (1)=0.906±0.013. We also perform a study of the impact of preliminary beyond zero-recoil lattice QCD calculations on the |Vcb| determinations. 
Additionally, we present the lepton flavor universality ratio Reμ=(B→D∗eν¯e)/(B→D∗μν¯μ)=0.990±0.021±0.023, the electron and muon forward-backward asymmetry and their difference ΔAFB=0.022±0.026±0.007, and the electron and muon D∗ longitudinal polarization fraction and their difference ΔFD∗L=0.034±0.024±0.007. The uncertainties quoted correspond to the statistical and systematic uncertainties, respectively.

Monday, January 16, 2023

Cousin Marriage Was Common In Minoan Crete And Bronze Age Greece

The three waves of migration revealed by ancient DNA from Crete conforms to the existing paradigm (and tends to support the connection of the Minoan language with pre-Indo-European Anatolian languages), but the high rate of cousin marriage there was a surprise. 

[O]n Crete and the other Greek islands, as well as on the mainland, it was very common to marry one's first cousin 4000 years ago. "More than a thousand ancient genomes from different regions of the world have now been published, but it seems that such a strict system of kin marriage did not exist anywhere else in the ancient world," says Eirini Skourtanioti, the lead author of the study who conducted the analyses.

From here, discussing the paper whose abstract and citation are as follows: 

The Neolithic and Bronze Ages were highly transformative periods for the genetic history of Europe but for the Aegean—a region fundamental to Europe’s prehistory—the biological dimensions of cultural transitions have been elucidated only to a limited extent so far. 
We have analysed newly generated genome-wide data from 102 ancient individuals from Crete, the Greek mainland and the Aegean Islands, spanning from the Neolithic to the Iron Age. We found that the early farmers from Crete shared the same ancestry as other contemporaneous Neolithic Aegeans. 
In contrast, the end of the Neolithic period and the following Early Bronze Age were marked by ‘eastern’ gene flow, which was predominantly of Anatolian origin in Crete. 
Confirming previous findings for additional Central/Eastern European ancestry in the Greek mainland by the Middle Bronze Age, we additionally show that such genetic signatures appeared in Crete gradually from the seventeenth to twelfth centuries BC, a period when the influence of the mainland over the island intensified. 
Biological and cultural connectedness within the Aegean is also supported by the finding of consanguineous endogamy practiced at high frequencies, unprecedented in the global ancient DNA record. Our results highlight the potential of archaeogenomic approaches in the Aegean for unravelling the interplay of genetic admixture, marital and other cultural practices.
Skourtanioti, E., Ringbauer, H., Gnecchi Ruscone, G.A. et al. "Ancient DNA reveals admixture history and endogamy in the prehistoric Aegean." Nat Ecol Evol (January 16, 2023). https://doi.org/10.1038/s41559-022-01952-3

The body text of the paper relates that:
In addition to this high frequency of distant genetic relatedness, we also report extraordinarily high levels of consanguinity (~50% of the 27 individuals) estimated from the runs of homozygosity (ROH) by performing hapROH on the genotyping data. The individual ROH histograms matched more with the expectations for parents being related to the degree of first cousins, half-siblings and aunt/uncle–nephew/niece. . . . Coupling the evidence for frequent distant relatives and cousin–cousin unions suggests that those individuals formed a small endogamous community that regularly practiced first-cousin intermarriages.

Intriguingly, endogamy is not a unique feature of Hagios Charalambos. We applied the method on another 61 Aegean individuals from all the periods that met recommended SNP coverage thresholds. In total, we found that ~30% of the individuals have most of their ROH in the bin of the longest ROH blocks, consistent with being offspring of parents related to a degree equivalent to first and second cousins. Offspring of close-kin unions were identified from the Neolithic through the LBA but due to the uneven sampling no conclusions can be drawn regarding temporal trends. Consanguinity was also present in higher frequency in the smaller islands of Salamis, Lazarides, Koukounaries and Koufonisia (50%) but overall it seemed common throughout the Aegean. The observed high frequency of endogamy diachronically points to a rather common social practice in the prehistoric Aegean that is so far unattested in the rest of the global aDNA record.

Science Should Be Democratic, But It Isn't A Democracy


Science should be democratic, in that it should be open to scientific contributions from anyone, and its stylistic conventions can be decided democratically. 

But science isn't a democracy. It is has different means of determining right and wrong.

Thursday, January 12, 2023

Calculating The Proton and Neutron Electric Dipole Moment

The Standard Model assumes, and there are multiple theoretical arguments to support, that there is no charge parity (CP) violation (which is equivalent to dependence upon the direction of time) in the strong force. 

There is an obvious place in the Standard Model equations of the strong force to insert a CP violation parameter, however, which is called the θ term. The θ term is zero if there is no CP violation in the strong force. 

But, while the theory assumes that the θ term is zero, experiments can never directly rule out a very small non-zero value for the θ term. 

A non-zero value for the θ term would have important qualitative implications, especially as a possible source of matter-antimatter asymmetry in the universe. The Standard Model and available observational evidence strongly support that this matter-antimatter asymmetry is an "initial condition" of the universe, contrary to the naive expectation that there should be equal amounts of matter and antimatter at the moment of the Big Bang. As a new paper discussed below explains:
Symmetries and their breaking are essential topics in modern physics, among which the discrete symmetries C (charge conjugation), P (parity), and T (time reversal) are of special importance. This is partially because the violation of the combined C and P symmetries is one of the three Sakharov conditions that are necessary to give rise to the baryon asymmetry of the universe (BAU). However, despite the great success of the standard model (SM), the weak baryogenesis mechanism from the CP violation within the SM contributes negligibly (∼ 16 orders of magnitude smaller than the observed BAU). This poses a hint that, besides the possible θ term in QCD, there could exist beyond-standard-model (BSM) sources of CP violation and thus the study of CP violation plays an important role in the efforts of searching for BSM physics.
One of the main ways to probe the magnitude of the θ term is to measure the electric dipole moments of the proton and the neutron, which are measurements that can be made with exquisite precision. No non-zero electric dipole moment has been observed for either the proton or the neutron. But strict upper bounds on this electromagnetic property of the nucleons have been established and those bounds can be incrementally improved over time.

A new paper uses Lattice quantum chromodynamics (QCD) methods to calculate from first principles the relationship between the observable quantities of the proton and neutron electric dipole moments, and the theoretical Standard Model parameter which is the θ term. 

The paper concludes that the electric dipole moment of the neutron is −0.00148(35)θ¯ e⋅fm and that the electric dipole moment of the proton is 0.0038(14)θ¯ e⋅fm. 

Thus, the θ term is about 675 times the magnitude of the neutron electric dipole moment and about 263 times the magnitude of the proton electric dipole moment, although both are zero if the θ term is zero (except for a weak force contribution about five orders of magnitude smaller than the current experimental limit). This also implies the the ratio of the electron dipole moment of the proton to the electron dipole moment of the neutron should be about -2.6.

The body text of the paper explains that:
The first experimental upper limit on the neutron EDM (nEDM) was given in 1957  as ∼ 10^−20 e·cm. During the past 60 years of experiments, this upper limit has been improved by 6 orders of magnitude. The most recent experimental result of the nEDM is 0.0(1.1)(0.2) × 10^−26 e·cm, which is still around 5 orders of magnitude larger than the contribution that can be offered by the weak CP violating phase. Currently, several experiments are aiming at improving the limit down to 10^−28 e·cm in the next ∼10 years. 
. . .

By using the most recent experimental upper limit of dn, our results indicate that θ¯ < 10^−10. 

This limit is equivalent to less than ± 1.2 x 10^-13 e·fm, which implies that the magnitude of the θ term must be less than about ± 10^-10, a constraint that will improve by about two orders of magnitude in the next decade.

This is too small by more than ten orders of magnitude to make a meaningful dent in the Sakharov conditions. The θ term would have to be roughly on O(1) after running to extremely high energy scales to explain the matter-antimatter asymmetry of the universe. But, the strong force becomes weaker, not stronger, at higher energy scales, so CP violation in the strong force should be less important at these energy scales, not more important.

Personally, I'm confident that the θ term is exactly zero, and that there are no new CP violating physics at higher energies, at least up to about the GUT scale, that explain the matter-antimatter asymmetry of the universe. 

Neither the zero value of the θ term, nor the existence of matter-antimatter asymmetry in the universe at a infinitesimal time after the Big Bang are "problems" in physics to be solved. They are simply descriptive features of our reality.

The paper and its abstract are as follows:
We calculate the nucleon electric dipole moment (EDM) from the θ term with overlap fermions on three domain wall lattices with different sea pion masses at lattice spacing 0.11 fm. Due to the chiral symmetry conserved by the overlap fermions, we have well defined topological charge and chiral limit for the EDM. Thus, the chiral extrapolation can be carried out reliably at nonzero lattice spacings. We use three to four different partially quenched valence pion masses for each sea pion mass and find that the EDM dependence on the valence and sea pion masses behaves oppositely, which can be described by partially quenched chiral perturbation theory. With the help of the cluster decomposition error reduction (CDER) technique, we determine the neutron and proton EDM at the physical pion mass to be dn=−0.00148(14)(31)θ¯ e⋅fm and dp=0.0038(11)(8)θ¯ e⋅fm. This work is a clear demonstration of the advantages of using chiral fermions in the nucleon EDM calculation and paves the road to future precise studies of the strong CP violation effects.
Jian Liang, et al., "Nucleon Electric Dipole Moment from the θ Term with Lattice Chiral Fermions" arXiv:2301.04331 (January 11, 2023).

Wednesday, January 11, 2023

Experiments Won't Trigger The Collapse Of The Universe

The best available measurements and theory suggest that given the mass of the Higgs boson and the running of various Standard Model physics parameters with energy scale, that the vacuum is only "metastable" and has a tiny probability of collapsing and ending the universe as we know it. But events like this are likely to happen only once in a period of time that is significantly longer than the current age of the universe.

A new preprint looks at whether ultra-high energy cosmic rays or particle collider concentrations of energy could trigger such a vacuum collapse.

Fortunately for us, the bottom line is that we are safe from that happening. We are many orders of magnitude in energy scales below the danger zone.

More Doubt Cast On Reactor Neutrino Anomalies

Yet another apparent experimental observation discrepancy from the Standard Model bites the dust, although, this particular one had already been in doubt anyway. I am personally confident there are no beyond the Standard Model sterile neutrinos.

Discrepancies between reactor neutrino experiments and theory may be the result of errors in the analysis of electron data that form the basis of the neutrino predictions.
From here. A synopsis of the Letter in the journal publishing it explains that:
Several experiments have been set up outside nuclear reactors to record escaping antineutrinos. The data generally agrees with theory, but at certain energies, the antineutrino flux is 6–10% above or below predictions. These so-called reactor antineutrino anomalies have excited the neutrino community, as they could be signatures of a hypothetical sterile neutrino (see Viewpoint: Getting to the Bottom of an Antineutrino Anomaly). But a new analysis by Alain Letourneau from the French Atomic Energy Commission (CEA-Saclay) and colleagues has shown that the discrepancies may come from experimental biases in associated electron measurements.

The source of reactor antineutrinos is beta decay, which occurs in a wide variety of nuclei (more than 800 species in a typical fission reactor). To predict the antineutrino flux, researchers have typically used previously recorded data on electrons, which are also produced in the same beta decays. This traditional method takes the observed electron spectra from nuclei, such as uranium-235 and plutonium-239, and converts them into predicted antineutrino spectra. But Letourneau and colleagues have found reason to doubt the electron measurements.

The team calculated antineutrino spectra—as well as the corresponding electron spectra—using a fundamental theory of beta decay. This method works for some nuclei, but not all, so the researchers plugged the gaps using a phenomenological model. They were able to treat all 800-plus reactor beta decays, finding “bumps” in the antineutrino flux that agree with observations. Similar features are predicted for electron spectra, but they don’t show up in the data. The results suggest that an experimental bias in electron observations causes the reactor antineutrino anomalies. To confirm this hypothesis, the researchers call for new precision measurements of the fission electrons.
The Letter and its abstract are as follows:
We investigate the possible origins of the reactor antineutrino anomalies in norm and shape within the framework of a summation model where β− transitions are simulated by a phenomenological model of Gamow-Teller decay strength. The general trends of divergence from the Huber-Mueller model on the antineutrino side can be reproduced in both norm and shape. From the exact electron-antineutrino correspondence of the summation model, we predict similar distortions in the electron spectra, suggesting that biases on the reference spectra of fission electrons could be the cause of the anomalies.

A science article aimed at the general public ends its story on this paper with this quote from a neutrino physicist:
“We still have other anomalies in neutrino physics that we cannot explain,” she says. But taking all neutrino studies together, Huber says, the evidence for the sterile neutrino isn’t very strong: “It’s not a good global fit to the data.”

The preprint of this Letter was previously blogged in this post

Rich Ancient DNA From Bell Beaker People In Bronze Age SE Spain

A rich ancient DNA collection from elite burials in Southeast Spain during the Bronze Age establishes that this society probably had hereditary leadership in a moderately complex society, was exogamous, and was patrilocal. A five generation long patriarchal dynasty is established made up of men with Y-DNA haplogroup R1b-Z195.

This isn't terribly surprising. A variety of past ancient DNA studies have established the steppe societies, generally, were patrilocal and exogamous. Likewise, hereditary rule was the most common form of political organization in premodern societies.

Wednesday, January 4, 2023

Progress Is Deciphering The Elamite Language

The Elamite language is a historically attested, but undeciphered language historically used in Southwestern Iran from about 2600 BCE to 330 BCE. One not widely accepted theory supposes that it is ancestral to the Dravidian languages of South Asia. But, the leading view is that it is a language isolate. The linked Wikipedia article about this language notes that:
A sizeable number of Elamite lexemes are known from the trilingual Behistun inscription and numerous other bilingual or trilingual inscriptions of the Achaemenid Empire, in which Elamite was written using Elamite cuneiform (circa 400 BC), which is fully deciphered. An important dictionary of the Elamite language, the Elamisches Wörterbuch was published in 1987 by W. Hinz and H. Koch. The Linear Elamite script however, one of the scripts used to write the Elamite language circa 2000 BC, has remained elusive until recently.
The approaches taken to decipher this language from the various scripts in which it is written resembles similar efforts to crack early Minoan and Greek written works.

Some recent developments in understanding its script came up in a review of two newly released books on the history of writing.
Being able to read a script is not the same as understanding a language. Even if the new hypothesis does find general acceptance, significant gaps will remain in our knowledge of Elamite grammar and vocabulary. It doesn’t help that Elamite is “isolated,” that is, unrelated to any other known tongue. All the same, there is now reasonable hope of translating what survives of the records these adventurous ancient traders left of their world.

Deciphering unknown languages often depends on the fact that the same language can be written in multiple scripts (as with Elamite, and later Turkish or Malay), and the same script can be used to write multiple languages (as with cuneiform, and later the Latin and Cyrillic alphabets).
A New York Times review of two new books on the history of writing via Language Log.

A paper published in 2022 claims to have almost fully deciphered the Linear Elamite script. The paper and its abstract are as follows:
Linear Elamite writing was used in southern Iran in the late 3rd/early 2nd millennium BCE (ca. 2300–1880 BCE). First discovered during the French excavations at Susa from 1903 onwards, it has so far resisted decipherment. 
The publication of eight inscribed silver beakers in 2018 provided the materials and the starting point for a new attempt; its results are presented in this paper. 
A full description and analysis of Linear Elamite of writing, employed for recording the Elamite language, is given here for the first time, together with a discussion of Elamite phonology and the biscriptualism that characterizes this language in its earliest documented phase.
Desset, François; Tabibzadeh, Kambiz; Kervran, Matthieu; Basello, Gian Pietro; Marchesi, Gianni "The Decipherment of Linear Elamite Writing". 112(1) Zeitschrift für Assyriologie und vorderasiatische Archäologie 11–60 (July 1, 2022) doi:10.1515/za-2022-0003.

Tuesday, January 3, 2023

The Lighter Side Of Gravity

I am a dad, so I am allowed to tell dad jokes.

LambdaCDM Is Still Inconsistent With JWST Observations

Someday, the mountain of data, including this factor of many, is going to get the consensus of astrophysicists and cosmologists to abandon the ΛCDM Standard Model of Cosmology.
JWST high redshift galaxy observations predict a higher star formation efficiency that the standard cosmology, which poses a new tension to ΛCDM. We find that the situation is worse than expected. 
The true situation is that the Planck CMB measurement has a strong tension with JWST high redshift galaxy observations. Specifically, we make a trial to alleviate this tension by considering alternative cosmological models including dark matter-baryon interaction, f(R) gravity and dynamical dark energy. Within current cosmological constraints from Planck-2018 CMB data, we find that these models all fail to explain such a large tension. 
A possible scenario to escape from cosmological constraints is the extended Press-Schechter formalism, where we consider the local environmental effect on the early formation of massive galaxies. Interestingly, we find that an appropriate value of nonlinear environmental overdensity of a high redshift halo can well explain this tension.
Deng Wang, Yizhou Liu, "JWST high redshift galaxy observations have a strong tension with Planck CMB measurements" arXiv:2301.00347 (January 1, 2023).

Sunday, January 1, 2023

Breakthrough Made In Numerically Solving Feynman Integrals

Theorists have found a way to solve complex Feynman integrals numerically by reducing them to simple linear algebra.
From Science.

If you don't know what that means, the article at the link does a decent job of explaining it at the undergraduate physics-math-engineering major level.

80% of new publications solving Feynman integrals used these theorists' open source code, which was released a year ago, to do so.

This is especially important for the physics of the strong force (that holds protons and neutrons made up of quarks together) a.k.a. QCD, and efforts to figure out quantum gravity, even though the article refers to the more familiar case of the quantum version of electromagnetism called quantum electrodynamics (QED for short).