A New Top Quark Mass Measurement

The latest top quark mass measurement at the Large Hadron Collider (LHC) is on the low side relative to previous measurements and the global average (which is 172.69 ± 0.30 from direct measurements), and is fairly precise despite using a fairly complex set of decay products to measure it. 

The new measurement is 1.93 sigma from the global average, so the new measurement is just barely consistent with the global average. In contrast, many other recent LHC measurements of the top quark mass have been high (almost two sigma high in at least one case) relative to the global average.

The mass of the top quark is measured in 36.3 fb−1 of LHC proton-proton collision data collected with the CMS detector at s√ = 13 TeV. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to five observables to extract the top quark mass. The top quark mass is measured to be 171.77 ± 0.37 GeV. This approach significantly improves the precision over previous measurements.

CMS Collaboration, "Measurement of the top quark mass using a profile likelihood approach with the lepton+jets final states in proton-proton collisions at s√ = 13 TeV" arXiv:2302.01967 (February 3, 2023).

Dark Matter Still Has Nothing On MOND In The Milky Way

The more complex dark matter particle mass models of the Milky Way, perform not better in describing what we see with other telescopes than the far simply MOND model when it comes to the Milky Way's rotation curve.

We use data from the Gaia DR3 dataset to estimate the mass of the Milky Way (MW) by analyzing the rotation curve in the range of distances 5 kpc to 28 kpc. 

We consider three mass models: the first model adds a spherical dark matter (DM) halo, following the Navarro-Frenk-White (NFW) profile, to the known stellar components. The second model assumes that DM is confined to the Galactic disk, following the idea that the observed density of gas in the Galaxy is related to the presence of more massive DM disk (DMD), similar to the observed correlation between DM and gas in other galaxies. The third model only uses the known stellar mass components and is based on the Modified Newton Dynamics (MOND) theory. 

Our results indicate that the DMD model is comparable in accuracy to the NFW and MOND models and fits the data better at large radii where the rotation curve declines but has the largest errors. For the NFW model we obtain a virial mass M(vir)=(6.5±0.3)×10^11M⊙ with concentration parameter c=14.5, that is lower than what is typically reported. In the DMD case we find that the MW mass is M(d)=(1.6±0.5)×10^11M⊙ with a disk's characteristic radius of Rd=17 kpc.

Francesco Sylos Labini, et al., "Mass models of the Milky Way and estimation of its mass from the GAIA DR3 data-set" arXiv:2302.01379 (February 2, 2023) (accepted for publication in The Astrophysical Journal).

Physics Needs Better Literature Reviews

One of my favorite physicists, Stacy McGaugh, reacting to a tweet expressing the same opinion by another of my favorite physicists, Sabine Hossenfelder, bemoans a cultural and institutional problem with the fundamental physics community that I agree is a serious one. 

What is it?

Physicists routinely publish papers that fail to review the literature sufficiently to identify the fact that previous published work already rules out, disproves, or contradicts the hypotheses that they are advancing in their papers.

It is a standard and almost universal practice that pretty much every thesis, dissertation, and published physics paper (other than a very short letter preliminarily reporting a very narrow measurement or result before a full length analysis of the results can be published) contains some review of the literature that brings the reader to the point of scientific knowledge where the matters being addressed by the authors in the new thesis, dissertation, or paper begins.

But, in many cases, this literature review is half-hearted and perfunctory, and misses key prior work relevant to the new paper.

For example, one of my pet peeves is when a paper says that their proposal is "well motivated" by concepts developed decades earlier that have later been found to be deeply flawed.

This isn't a "mortal sin". The physics literature is vast and it grows every week. Not everyone in the discipline can devote the time that I do to reading every abstract in a whole range of related fundamental physics categories every day when it comes out on arXiv. And, there are multiple ways of looking at a problem that can make identifying relevant papers challenging (the same issue comes up in doing patent and trademark searches, or searching for precedents related to a legal issue).

But, if you are going to be advancing a new hypothesis in this field, you really should do a proper literature review (and more generally, you should really know the literature relevant to your work from multiple perspectives) before advancing theories that are contradicted by other observational evidence or theoretical considerations that you don't mention or engage with in your paper.

You don't have to agree with everything else that has ever been published. Sometimes previously published papers are incorrect and you are right. But when that happens, rather than ignoring what previously published papers have to say, you really should engage with prior contradictory papers and explain why you think that their observations or analysis is flawed or inapplicable, and thus doesn't actually contradict your work.

You don't necessarily have to spell out the contradictions or flaws of the prior work in full in every new paper in a series of papers developing an idea. It is sufficient to do it once in your first paper identifying what you believe is a flaw in prior work and then to cite that that discussion, incorporating it by reference and with a brief mention, in later papers. But that is very different from ignoring contradictory prior work entirely.

If the authors of physics papers did more diligent and comprehensive literature reviews (and peer reviewers did a better job of insisting on better quality reviews of the literature which would catch both many innocent omissions and many cases where prior contradictory work is willfully ignored), the quality of the papers that did get published would be greater. This is because a lot of speculative garbage papers that ignore known insurmountable obstacles to their work would be dropped before they were presented.

Mirror Cosmology Recapped

Here is a recap, all in one place, of work on mirror cosmology with an anti-matter universe before the Big Bang that is a mirror of our own and our own matter dominated universe that I've previously blogged, stripped of (probably wrong) speculations about dark matter and right handed neutrinos:

We argue that the Big Bang can be understood as a type of mirror. We show how reflecting boundary conditions for spinors and higher spin fields are fixed by local Lorentz and gauge symmetry, and how a temporal mirror (like the Bang) differs from a spatial mirror (like the AdS boundary), providing a possible explanation for the observed pattern of left- and right-handed fermions. By regarding the Standard Model as the limit of a minimal left-right symmetric theory, we obtain a new, cosmological solution of the strong CP problem, without an axion.

Latham Boyle, Martin Teuscher, Neil Turok, "The Big Bang as a Mirror: a Solution of the Strong CP Problem" arXiv:2208.10396 (August 22, 2022). The body text states:

In a series of recent papers, we have argued that the Big Bang can be described as a mirror separating two sheets of spacetime. Let us briefly recap some of the observational and theoretical motivations for this idea.

Observations indicate that the early Universe was strikingly simple: a fraction of a second after the Big Bang, the Universe was radiation-dominated, almost perfectly homogeneous, isotropic, and spatially flat; with tiny (around 10^−5) deviations from perfect symmetry also taking a highly economical form: random, statistically gaussian, nearly scale-invariant, adiabatic, growing mode density perturbations. Although we cannot see all the way back to the bang, we have this essential observational hint: the further back we look (all the way back to a fraction of a second), the simpler and more regular the Universe gets. This is the central clue in early Universe cosmology: the question is what it is trying to tell us.

In the standard (inflationary) theory of the early Universe one regards this observed trend as illusory: one imagines that, if one could look back even further, one would find a messy, disordered state, requiring a period of inflation to transform it into the cosmos we observe.

An alternative approach is to take the fundamental clue at face value and imagine that, as we follow it back to the bang, the Universe really does approach the ultra-simple radiation-dominated state described above (as all observations so far seem to indicate).

Then, although we have a singularity in our past, it is extremely special. Denoting the conformal time by τ , the scale factor a(τ) is ∝ τ at small τ so the metric g^(µν) ∼ a(τ)^(2ηµν) has an analytic, conformal zero through which it may be extended to a “mirror-reflected” universe at negative τ.

[W]e point out that, by taking seriously the symmetries and complex analytic properties of this extended two-sheeted spacetime, we are led to elegant and testable new explanations for many of the observed features of our Universe including: . . . (ii) the absence of primordial gravitational waves, vorticity, or decaying mode density perturbations; (iii) the thermodynamic arrow of time (i.e. the fact that entropy increases away from the bang); and (iv) the homogeneity, isotropy and flatness of the Universe, among others.

In a forthcoming paper, we show that, with our new mechanism for ensuring conformal symmetry at the bang, this picture can also explain the observed primordial density perturbations.

In this Letter, we show that: (i) there is a crucial distinction, for spinors, between spatial and temporal mirrors; (ii) the reflecting boundary conditions (b.c.’s) at the bang for spinors and higher spin fields are fixed by local Lorentz invariance and gauge invariance; (iii) they explain an observed pattern in the Standard Model (SM) relating left- and right-handed spinors; and (iv) they provide a new solution of the strong CP problem. . . .

In this paper, we have seen how the requirement that the Big Bang is a surface of quantum CT symmetry yields a new solution to the strong CP problem. It also gives rise to classical solutions that are symmetric under time reversal, and satisfy appropriate reflecting boundary conditions at the bang.

The classical solutions we describe are stationary points of the action and are analytic in the conformal time τ. Hence they are natural saddle points to a path integral over fields and four-geometries. The full quantum theory is presumably based on a path integral between boundary conditions at future and past infinity that are related by CT-symmetry. The cosmologically relevant classical saddles inherit their analytic, time-reversal symmetry from this path integral, although the individual paths are not required to be time-symmetric in the same sense (and, moreover may, in general, be highly jagged and non-analytic).

We will describe in more detail the quantum CT-symmetric ensemble which implements (12), including the question of whether all of the analytic saddles are necessarily time-symmetric, and the calculation of the associated gravitational entanglement entropy, elsewhere.

Another paper discusses one of the earlier papers by the authors above and elaborates on the foundation of their work:

In a recent work, Turok, Boyle and Finn hypothesized a model of universe that does not violate the CPT-symmetry as alternative for inflation. With this approach they described the birth of the Universe from a pair of universes, one the CPT image of the other, living in pre- and post-big bang epochs. The CPT-invariance strictly constrains the vacuum states of the quantized fields, with notable consequences on the cosmological scenarios.

Here we examine the validity of this proposal by adopting the point of view of archaic cosmology, based on de Sitter projective relativity, with an event-based reading of quantum mechanics, which is a consequence of the relationship between the universal information reservoir of the archaic universe and its out-of-equilibrium state through quantum jumps. In this scenario, the big bang is caused by the instability of the original (pre)vacuum with respect to the nucleation of micro-events that represent the actual creation of particles.

Finally, we compare our results with those by Turok et al., including the analytic continuation across the big bang investigated by Volovik and show that many aspects of these cosmological scenarios find a clear physical interpretation by using our approach. Moreover, in the archaic universe framework we do not have to assume a priori the CPT-invariance like in the other models of universe, it is instead a necessary consequence of the archaic vacuum structure and the nucleation process, divided into two specular universes.

Ignazio Licata, Davide Fiscaletti, Leonardo Chiatti, Fabrizio Tamburini, "CPT Symmetry in Projective de Sitter Universes" arXiv:2002.07550 (February 18, 2020).

The universe before the Big Bang is the CPT reflection of the universe after the bang, so that the state of the universe does not spontaneously violate CPT. The universe before the bang and the universe after the bang may be viewed as a universe/anti-universe pair, created from nothing. The early universe is radiation dominated and inflationary energy is not required. We show how CPT selects a preferred vacuum state for quantum fields on such a cosmological spacetime. This, in turn, leads to a new view of the cosmological matter/anti-matter asymmetry[.]

Latham Boyle, Kieran Finn, Neil Turok, "The Big Bang, CPT, and neutrino dark matter" arXiv:1803.08930 (March 23, 2018).

Some of their key earlier papers by some of these authors (which I haven't yet read and don't necessarily endorse) are: "Gravitational entropy and the flatness, homogeneity and isotropy puzzles" arXiv:2201.07279, "Two-Sheeted Universe, Analyticity and the Arrow of Time" arXiv:2109.06204, and "CPT-Symmetric Universe" arXiv:1803.08928. 

In the multiverse, the universes can be created in entangled pairs with spacetimes that are both expanding in terms of the time variables experienced by internal observers in their particle physics experiments. The time variables of the two universes are related by an antipodal-like symmetry that might explain why there is no antimatter in our universe: at the origin, antimatter is created, by definition and for any observer, in the observer's partner universe. The Euclidean region of the spacetime that separates the two universes acts as a quantum barrier that prevents matter-antimatter from collapse.

Salvador J. Robles-Perez, "Restoration of matter-antimatter symmetry in the multiverse" arXiv:1706.06304 (June 20, 2017).

Cosmological inflation:

In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10^−36 seconds after the conjectured Big Bang singularity to some time between 10^−33 and 10^−32 seconds after the singularity. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago). . . . It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe. Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.

Magnetic monopoles are already a non-existent problem so in this respect, cosmological inflation is merely ruling out a rubbish theory with no observational support.

Galaxies Ten Billion Years Ago Look A Lot Like Galaxies Today

The LambdaCDM model expects galaxies to take longer to appear when they do and to evolve significantly over time scales of billions of years. But, the latest observations of galaxies as much as 10 billion years old suggest that galaxies then had basically the same dynamics that they do now

We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z≃1.47 and zC-400569 at z≃2.24) using new high-resolution ALMA observations of multiple 12CO transitions. For zC-400569 we also re-analyze high-quality Hα data from the SINS/zC-SINF survey. 

We find that (1) Both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∼8 kpc contrary to previous results pointing to outer declines in the rotation speed Vrot; (2) The intrinsic velocity dispersions are low (σCO≲15 km/s for CO and σHα≲37 km/s for Hα) and imply Vrot/σCO≳17−22 yielding no significant pressure support; (3) Mass models using HST images display a severe disk-halo degeneracy: models with inner baryon dominance and models with "cuspy" dark matter halos can fit the rotation curves equally well due to the uncertainties on stellar and gas masses; (4) Milgromian dynamics (MOND) can successfully fit the rotation curves with the same acceleration scale a0 measured at z≃0. 

The question of the amount and distribution of dark matter in high-z galaxies remains unsettled due to the limited spatial extent of the available kinematic data; we discuss the suitability of various emission lines to trace extended rotation curves at high z. Nevertheless, the properties of these two high-z galaxies (high Vrot/σV ratios, inner rotation curve shapes, bulge-to-total mass ratios) are remarkably similar to those of massive spirals at z≃0, suggesting weak dynamical evolution over more than 10 Gyr of the Universe's lifetime.

Federico Lelli, Zhi-Yu Zhang, Thomas G. Bisbas, Lingrui Lin, Padelis Papadopoulos, James M. Schombert, Enrico Di Teodoro, Antonino Marasco, Stacy S. McGaugh, "Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy" arXiv:2302.00030 (January 31, 2023) (Accepted for publication in Astronomy and Astrophysics).

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.

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. 

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.

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.

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.

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.

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).

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. Letourneau, et al., "Origin of the Reactor Antineutrino Anomalies in Light of a New Summation Model with Parametrized β− Transitions"130 Phys. Rev. Lett. 021801 (January 10, 2023).

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.

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.

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).

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).