Atomic Nuclei Described At Quark-Gluon Level

Context

Once of the things that physicists can do, even if our understanding of the laws of physics is complete, is to formally derive the properties of more complex structures, like atoms, from the fundamental laws of physics found in the Standard Model. 

We understand the structure of atoms mostly in the context of a simplified proton-neutron-electron model, that is used in chemistry and even, for the most part, in nuclear physics, with a simplified (mostly experimentally fit) binding energy description of how protons and neutrons are held together in atomic nuclei that describes the residual strong force that holds protons and neutrons in the atom together in a nucleus (that we know is mediated mostly by composite pions as force carriers and to a secondary extent by force carrying composite kaons, rather than directly by gluons). 

The Standard Model of Particle physics provides a more fundamental description of protons, neutrons, and their interactions in terms of quarks and gluons with its model of the strong force that binds quarks and gluons to each other that is mediated by force carrying gluons. This theory is called quantum chromodynamics (QCD) because the analogy to electric charge for the strong force is called "color charge". Quarks can have one of three color charges, and gluons come in eight combinations that involve pairs of color charges.

The New Paper

Half a century after the Standard Model was devised, a new paper has made a major breakthrough at advancing the unfinished project of explaining atomic nuclei in terms of quarks and gluons, rather than in terms of composite protons and neutrons bound by the residual strong force.

The new paper accurately reproduces the structure of 18 atomic different nuclei with quantum chromodynamics (the theory of the Standard Model strong force that binds quarks and gluons to each other).

The parton distribution functions (PDFs) describe the structure of a composite particle in terms of quarks and gluons. PDFs can be calculated, in theory, from first principles in the Standard Model without any experimental input beyond the values of the two dozen or so experimentally measured physical constants of the Standard Model. 

But until less than a decade ago, in practice, parton distribution functions were almost always created by a vast statistical data dump from billions of collisions to which a mathematical function was fitted, that were very particular to particular particles at particular energy scales. These were updated from time to time with new data from more collisions. 

When it has been done previously from first principles, this has mostly been confined to individual protons, neutrons, or other simple hadrons such as pions (hadrons are composite particles whose particles are bound by gluons), not to multi-hadron atoms.

The new paper make some big leaps beyond that, advancing the project of rigorously demonstrating what we had merely assumed (for some good reasons) for the last fifty years: that the structure of atomics can be described fully from first principles using the Standard Model.

I quote at length from a secondary source account of what the paper is doing, because the paper itself is too technical for a general audience and what the paper is doing is sufficiently technical that I don't want to mangle it in my paraphrased retelling of it.

The atomic nucleus is made up of protons and neutrons, particles that exist through the interaction of quarks bonded by gluons. It would seem, therefore, that it should not be difficult to reproduce all the properties of atomic nuclei hitherto observed in nuclear experiments using only quarks and gluons. However, it is only now that an international team of physicists has succeeded in doing this. . . .

This long-standing deadlock has only now been broken, in a paper published in Physical Review Letters. Its main authors are scientists from the international nCTEQ collaboration on quark-gluon distributions.

"Until now, there have been two parallel descriptions of atomic nuclei, one based on protons and neutrons which we can see at low energies, and another, for high energies, based on quarks and gluons. In our work, we have managed to bring these two so far separated worlds together," says Dr. Aleksander Kusina, one of the three theoreticians from the Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) participating in the research. . . .

Experiments . . . show that when electrons have relatively low energies, atomic nuclei behave as if they were made of nucleons (i.e. protons and neutrons), whereas at high energies, partons (i.e. quarks and gluons) are "visible" inside the atomic nuclei.

The results of colliding atomic nuclei with electrons have been reproduced quite well using models assuming the existence of nucleons alone to describe low-energy collisions, and partons alone for high-energy collisions. However, so far these two descriptions have not been able to be combined into a coherent picture.

In their work, physicists from the IFJ PAN used data on high-energy collisions, including those collected at the LHC accelerator at CERN laboratory in Geneva. The main objective was to study the partonic structure of atomic nuclei at high energies, currently described by parton distribution functions (PDFs).

These functions are used to map how quarks and gluons are distributed inside protons and neutrons and throughout the atomic nucleus. With PDF functions for the atomic nucleus, it is possible to determine experimentally measurable parameters, such as the probability of a specific particle being created in an electron or proton collision with the nucleus.

From the theoretical point of view, the essence of the innovation proposed in this paper was the skillful extension of parton distribution functions, inspired by those nuclear models used to describe low-energy collisions, where protons and neutrons were assumed to combine into strongly interacting pairs of nucleons: proton-neutron, proton-proton and neutron-neutron.

The novel approach allowed the researchers to determine, for the 18 atomic nuclei studied, parton distribution functions in atomic nuclei, parton distributions in correlated nucleon pairs and even the numbers of such correlated pairs.

The results confirmed the observation known from low-energy experiments that most correlated pairs are proton-neutron pairs (this result is particularly interesting for heavy nuclei, e.g. gold or lead). Another advantage of the approach proposed in this paper is that it provides a better description of the experimental data than the traditional methods used to determine parton distributions in atomic nuclei.

"In our model, we made improvements to simulate the phenomenon of pairing of certain nucleons. This is because we recognized that this effect could also be relevant at the parton level. Interestingly, this allowed for a conceptual simplification of the theoretical description, which should in future enable us to study parton distributions for individual atomic nuclei more precisely," explains Dr. Kusina.

The agreement between theoretical predictions and experimental data means that, using the parton model and data from the high-energy region, it has been possible for the first time to reproduce the behavior of atomic nuclei so far explained solely by nucleonic description and data from low-energy collisions. The results of the described studies open up new perspectives for a better understanding of the structure of the atomic nucleus, unifying its high- and low-energy aspects.

From Phys.org. The paper and its abstract are as follows:

We extend the QCD Parton Model analysis using a factorized nuclear structure model incorporating individual nucleons and pairs of correlated nucleons. Our analysis of high-energy data from lepton deep-inelastic scattering, Drell-Yan, and 𝑊 and 𝑍 boson production simultaneously extracts the universal effective distribution of quarks and gluons inside correlated nucleon pairs, and their nucleus-specific fractions. Such successful extraction of these universal distributions marks a significant advance in our understanding of nuclear structure properties connecting nucleon- and parton-level quantities.

A. W. Denniston, et al, "Modification of Quark-Gluon Distributions in Nuclei by Correlated Nucleon Pairs", 133 Physical Review Letters 152502 (October 11, 2024). DOI: 10.1103/PhysRevLett.133.152502

An earlier pre-print related to this paper can be found at arXiv, but the open access version of this paper is not yet available at arXiv.

Ancient South African DNA

A new paper on South African ancient DNA isn't paradigm shifting but does pin down more precisely when outsiders from different places began to admix with local hunter-gatherers and the extent to which that mixture involved mostly male outsiders who replaced a significant share of local hunter-gatherer men in the gene pool. 

Most admixture between South African hunter-gatherers, West African derived Bantus, and East African herders, took place starting around roughly 900 CE to 1500 CE (i.e. during the European Middle Ages). European admixture with Southern Africans begins in earnest around 1800 CE. All of this admixture with outsiders was male outsider dominated.

Joscha Gretzinger, et al., "9,000 years of genetic continuity in southernmost Africa demonstrated at Oakhurst rockshelter" (October 2024) provides ancient DNA from 10,000 to 1,300 years old (based upon radiocarbon dates) from the Southern tip of South Africa. (Hat tip to Bernard).

The Khoi-San hunter-gatherers of Southern Africa have largely been forced into the Kalahari desert to the north, but still have a north-south cline genetically, and these ancient DNA samples are towards the southern edge of that cline, although not at the actual bottom of it, as one might expect, with the greatest similarity to the Khomani San (who are part of the Tuu linguistic family).

Bernard recounts from the paper (as translated from the French by Google) that:

None of these individuals have any genetic affinity with other African populations, even the most recent dated 1300 years ago, suggesting that the non-San component arrived in South Africa more recently than 1300 years ago. On the other hand, all the ancient Oakhurst individuals older than 4000 years ago as well as the other ancient South Africans from St. Helena, Faraoskop and Ballito Bay, dated between 2200 and 1300 years ago, are genetically indistinguishable. 

Then the authors highlighted a genetic discontinuity between 1300 and 400 years ago relative to the arrival of populations from northeastern Africa in South Africa. All these results suggest a very strong genetic continuity between 10,000 and 1300 years ago in South Africa, while the Oakhurst population does not show any sign of particular isolation as shown by the analysis of heterozygous segments.

The authors then investigated recent genetic admixtures in South Africa with the Northeast and West African components. To do this, they used the qpAdm software on contemporary San, Khoe and Bantu individuals with no European ancestry. They thus highlighted the older arrival of the Northeast African component (1068 years on average) compared to the arrival of the West African component (808 years on average among Bantu populations and 578 years among San and Khoe populations). This last result suggests the arrival of several waves of Bantu migration in South Africa, or a continuous flow of arrival of this population over several centuries:

On the other hand, the authors highlighted a sexual bias in these genetic admixture events. Thus, the San, Khoe and Bantu populations have more South African components in the X chromosome than in the autosomes, suggesting that there are more San women than men among the ancestors of contemporary populations, and therefore more men than women from Northeast Africa or West Africa. The ratio of the number of San women to the number of San men among the ancestors of current populations is estimated at 1.4 for the Damara population, 2.28 for the Hoan population, 4 for the Shua population, 5.2 for the Haiom population and 2.1 for the Bantu population of South Africa.

Finally, the authors highlighted a recent sexual bias corresponding to the arrival of men from Northwestern Europe in South Africa dated on average 199 years ago.

As another recent paper demonstrated, Southern African hunter-gatherers were genetically isolated from other modern humans for about 300,000 years (until about 1,100 years ago as indicated by this paper). 

Indirect Constraints On Dark Matter-Ordinary Matter Interactions

This very clever analysis strongly constrains the existence of non-gravitational long range interactions between dark matter and ordinary matter. 

Yet, the strong correlation of ordinary matter distributions and inferred dark matter halos, which necessarily follows from, among other things, the radial acceleration relation (RAR), requires such a force. So, this helps to prove that dark matter does not exist and the dark matter phenomena must be a function of modified gravity or a fifth force.

Dark matter's existence is known thanks to its gravitational interaction with Standard Model particles, but it remains unknown whether this is the only force present between them. While many searches for such new interactions with dark matter focus on short-range, contact-like interactions, it is also possible that there exist weak, long-ranged forces between dark matter and the Standard Model. In this work, we present two types of constraints on such new interactions. 

First, we consider constraints arising from the fact that such a force would also induce long range interactions between Standard Model particles themselves, as well as between dark matter particles themselves. Combining the constraints on these individual forces generally sets the strongest constraints available on new Standard Model-dark matter interactions. 

Second, we consider the possibility of constraining new long-ranged interactions between dark matter and the Standard Model using the effects of dynamical friction in ultrafaint dwarf galaxies, especially Segue I. Such new interactions would accelerate the transfer of kinetic energy from stars to their surrounding dark matter, slowly reducing their orbits; the present-day stellar half-light radius of Segue I therefore allows us to exclude new forces which would have reduced stars' orbital radii below this scale by now.

Zachary Bogorad, Peter Graham, Harikrishnan Ramani, "Constraints on Long-Ranged Interactions Between Dark Matter and the Standard Model", arXiv:2410.07324 (October 9, 2024).

The Nobel Prize In Chemistry In 2024

Commentators have noted the AI trend in both the physics and the chemistry awards this year. 

The Nobel Prize in Chemistry was awarded on Wednesday to three scientists for discoveries that show the potential of advanced technology, including artificial intelligence, to predict the shape of proteins, life’s chemical tools, and to invent new ones.

The laureates are: Demis Hassabis and John Jumper of Google DeepMind, who used A.I. to predict the structure of millions of proteins; and David Baker of the University of Washington, who used computer software to invent a new protein.

From the New York Times. 

Does Gravity Screen UV Divergences?

This article falls in the category of technical, but potentially important. And the fact that this is framed as a homage to Stanley Deser, one of the leading late 20th century GR theorists, means that it could gain traction, in the face of sociological rooted resistance to paradigm breaking ideas in astrophysics. 

Ultraviolet (i.e. high energy) divergences are a major barrier to quantum gravity theories, rendering gravity non-renormalizable. But this article explores the possibility that non-perturbative approaches to GR could solve that problem, which has been a major roadblock in quantum gravity theories. Deur's approach to explaining dark matter and dark energy phenomena also involve resort to non-perturbative GR effects.

In the peculiar manner by which physicists reckon descent, this article is by a "child" and "grandchild" of the late Stanley Deser. We begin by sharing reminiscences of Stanley from over 40 years. Then we turn to a problem which was dear to his heart: the prospect that gravity might nonperturbatively screen its own ultraviolet divergences and those of other theories. After reviewing the original 1960 work by ADM, we describe a cosmological analogue of the problem and then begin the process of implementing it in gravity plus QED.

R. P. Woodard and B. Yesilyurt, "The Other ADM" arXiv:2410.05213 (October 7, 2024).

The introduction begins as follows (in selected parts):

Stanley Deser was the Grand Old Man of quantum gravity. Everyone in the f ield knew him, and the vast majority of us loved him. His life was a testament to the persistence of scientific inquiry, optimism and simple humanity over the course of a turbulent century. . . . He graduated college at 18, and took a Ph.D from Harvard at age 22. In a career spanning seven decades he is credited with hundreds of publications, including 8 papers and a book written after the age of 90. 

. . . 

Gravity needed him: despite the lovely geometrical formulation of its early days, general relativity was not then a proper field theory. There was no canonical formalism, with its careful enumeration of the degrees of freedom and their contribution to the total energy. Hence there was no way to prove classical stability, no way to develop numerical integration techniques and no way to even begin thinking about quantization. In a memorable sequence of papers with Dick Arnowitt and Charlie Misner, Stanley sorted out the gauge issue, identified canonical variables and defined an energy functional for asymptotically flat geometries. Stanley would return to the problem of gravitational energy later on in his career. 

With Claudio Teitelboim (now Bunster) he established the stability of supergravity. And he collaborated with Larry Abbott to prove the classical stability of gravity with a positive cosmological constant. Stanley was a consummate collaborator: 

• With David Boulware he showed that endowing the graviton with a mass inevitably results in a ghost mode, provided that the theory has a smooth perturbative limit. 

• With Peter van Nieuwenhuizen he extended the work of ’t Hooft and Veltman to show that renormalizability is lost at one loop when general relativity is combined with either electromagnetism, Yang-Mills theory, or Dirac fermions. 

• With Bruno Zumino he showed that consistently coupling a spin 3/2 gravitino to gravity produces a locally supersymmetric theory. The two then applied their formalism to string theory and to the breaking of supersymmetry. 

• With Mike Duff and Chris Isham he identified the first true conformal anomaly, which led to a classification scheme with Adam Schwimmer. 

• With Roman Jackiw and Stephen Templeton he showed that adding a dimensionally-reduced Chern-Simons term to Yang-Mills or gravity results in massive particles of spin 1 and 2, respectively. 

• With Gerard ’t Hooft and Roman Jackiw he explained how to understand general relativity in 2 + 1 dimensions. 

• With Cedric Deffayet and Gilles Esposito-Farese he extended flat space Galileons to curved space. . . .

Then the two authors turn to a problem which long fascinated Stanley: the possibility that quantum gravity might regulate its own ultraviolet divergence problem and even those of other theories. We first review ADM’s prescient and thought-provoking demonstration that classical gravitation cancels the self-energy divergence of a point charge. This is “the other ADM” of our title. We then describe a quantum field theoretic analogue of the same basic effect in the context of inflationary cosmology. The next section discusses the prospects for implementing the ADM mechanism in general relativity plus QED on an asymptotically flat background. 

Part 3 of the paper explains this ADM mechanism:

The idea that gravity might regulate divergences is based on the fact that gravitational interaction energy is negative. 

For example, this makes the mass of the Earth-Moon system slightly smaller than the sum of their masses, even when one includes the kinetic energy of their orbital motion, 

M(EM)=M(E)+M(M)−(GM(E)M(M)/(2c^2R)). (1) 

The decrease works out to about 6 × 10^11 kilograms, which makes for a fractional reduction of 10^−13. Note that the fractional reduction becomes larger as the orbital radius R decreases. In 1960 Arnowitt, Deser and Misner quantified the mechanism in the context of a classical (in the sense of non-quantum) charged and gravitating point particle. Although they solved the full general relativistic constraints and then computed the ADM mass, their result can be understood using a simple model that they devised. 

Suppose the particle has a bare mass M(0) and charge Q, and is regulated as a spherical shell of radius R. Then its rest mass energy might be expressed as, 

M(R)c^2 = M(0)c^2 + Q^2/(8πε(0)R)−(GM^2(R)/(2R)), (2) 

where the single concession to relativity is that the Newtonian gravitational interaction energy has been evaluated using the total mass. Of course the quadratic equation (2) can be solved to give, 

M(R) = c^2R/G(√(1+(2GM(0)/(Rc^2)) + (GQ^2/(4πε(0)R^2c^4))) − 1). (3)

The unregulated limit is finite and independent of the bare mass,  

lim R→0 M(R) = √(Q^2/(4πε(0)G)). (4)

Three crucial points about the result (4) deserve mention: 

• It is finite; (3) (4) 

• It is independent of the bare mass M(0), as long as that is finite; and 

• It is nonperturbative. 

Of course finiteness results from the fact that gravitational interaction energy is negative. This is evident from expression (2). The Q^2/(8πǫ(0)R) term means that compressing a shell of charge costs energy, however, the −GM^2/(2R) term signals that gravity is able to pay the bill, no matter how high. 

The fact that any fixed M(0) drops out is also evident from expression (2). Note that this is not at all how a conventional particle physicist would have approached the problem. Our conventional colleague would have regarded the total mass M as a measured quantity and then required the bare mass to depend upon the regulating parameter R so as to force the result to agree with measurement, 

M(0)(R) = M(meas) − Q^2/(8πε(0)Rc^2) + GM(meas)^2/(2Rc^2) . (5) 

That is how renormalization works. It is unavoidable without gravity, but the presence of gravity opens up the fascinating prospect of computing fundamental particle masses from first principles. Setting Q = e in expression (4) gives an impossibly large result for the electron, 

√(e^2/(4πε(0)G) = √(e^2/(4πε(0)ℏc) × √(ℏc/G) = √α × M(Planck). (6)

However, it is well known that quantum field theoretic effects often the linear self-energy divergence of a classical electron to alogarithmic divergence. 

This opens the possibility of the true relation containing exponentials. For example, one gets within a factor of four with, 

M(electron)=√α x M(Planck) × exp(− 1/(e^1 x α)) ≈ 0.134 MeV, (7)

[Ed. the measured value of the electron mass is 0.51099895000 ± 0.00000000015 MeV]

where e^1≈2.71828 is the base of the natural logarithm. The electron also carries weak charge, which should enter at some level. Perhaps all fundamental particle masses can be computed from first principles? One might even hope that the mysterious generations of the Standard Model appear as “excited states” in such a picture.

The nonperturbative nature of the ADM mechanism is evident from the fact that (4) goes like the square root of the fine structure constant and actually diverges as Newton’s constant goes to zero. The perturbative result comes from expanding the square root of (3) in powers of Q^2 and G, 

M(R)= (M(0)+ Q^2/(8πε(0)Rc^2)) x [1 

− 1/4(2GM(0)/(Rc^2) + GQ^2/(4πε(0)R2c4)) 

+ 1/8 (2GM(0)/(Rc^2) + GQ^2/(4πε(0)R^2c^4)^2 

− 5/64(2GM(0)/(Rc^2) + GQ^2/4πε(0)R^2c^4)^3 

+ ...] . (8) 

This is a series of ever-higher divergences. Of course perturbation theory becomes invalid for large values of the expansion parameter, 

2GM(0)/(Rc^2) + GQ^2/(4πε(0)R^2c^4). (9) 

Perhaps the same problem invalidates the use of perturbation theory in quantum general relativity, which would show cancellations like (4) if only we could devise a better approximation scheme? It is hopeless trying to perform a genuinely nonperturbative computation. However, a glance at the expansion (8) shows what goes wrong with conventional perturbation theory: gravity has no chance to“keep up” with the gauge sector. The lowest electromagnetic divergence is Q^2/(8πε(0)Rc^2), whereas gravity’s first move to cancel comes at order −[Q^2/(4πε(0)Rc^2)]^2 × G/(8Rc^2).

What is needed is are organization of perturbation theory in which the gravitational response comes at the“same order”as the gravitational response. Several studies have searched for such an expansion without success. 

The paper concludes with the material quoted below:

Stanley Deser was a great physicist and a good man who left the world a better place. Section 1 reviews some of his most important contributions to physics while section 2 presents personal reminiscences from one of his students. The remainder of the paper is devoted to one motivation for Deser’s early fascination with quantum gravity: the possibility that it might regulate its own divergences and those of other theories. This possibility arises because the gravitational interaction energy is negative, and sourced by the same sectors which diverge.

Section 3 reviews the example ADM discovered of how classical (that is, non-quantum) general relativity cancels the famous linear divergence of a point charged particle. The final result (4) is not only finite but also independent of the bare mass, as long as that is finite. This raises the fascinating prospect of not only solving the problem of quantum gravity but also computing fundamental particle masses from first principles. It is impossible to overstate the revolution this would work on our perception of quantum gravity. From a sterile issue of logical consistency, without observable consequences at ordinary energies, and only perturbatively small effects even at the fantastic scales of primordial inflation, quantum gravity would be thrust to center stage. Every measurement of a fundamental particle mass would represent a sensitive check. One might even hope that the mysterious 2nd and 3rd generations of the Standard Model emerged as excited states of the 1st generation.

Of course there is a catch: one must make the calculation nonperturbatively in an interacting quantum field theory. This is evident from how its classical limit (4) depends upon α and G. There seems little hope of ever being able to perform an exact computation in an interacting 3 + 1 dimensional quantum field theory. What is needed instead is a way of reorganizing conventional perturbation theory so that the negative energy constrained degrees of freedom have a chance to “keep up” with the positive energy, unconstrained degrees of freedom. The key to this seems to be solving the Hamiltonian Constraint. 

Section 4 describes how one accomplishes just that in the theory of primordial inflation. Fittingly, the solution (24) is given using ADM variables. Although it is not clear if this form regulates the usual ultraviolet divergences of gravity with a scalar, the weak field expansion (25) of the gauge-fixed and constrained action does show an ADM-like erasure of the scalar perturbation except for those parts protected by the nonzero first slow roll parameter ǫ.

Section 5 represents our initial attempt to implement the ADM mechanism for Quantum Electrodynamics + General Relativity. Although it is clear that the Hamiltonian Constraint can be solved exactly, a number of issues remain, the most important of which is how to extract “background” parts of the kinetic and potential energies so as to keep quantum corrections small. We look forward to further study of this system.

This Year's Nobel Prizes In STEM

The Nobel Prize in Physics for 2024 was awarded to John J. Hopfield and Geoffrey E. Hinton for their work in using machine learning methods (specifically, neural networks, a form of artificial intelligence) to solve physics problems. 

Both my son and his girlfriend currently work in the AI industry (and my brother and my daughter both work in the larger IT industry), so this is highly relevant to me personally. The large language models (LLMs) used in my own industry, law, are getting dramatically better by the year, but are still not ready for prime time and are prone to making things up and reaching absurd conclusions.

The prize in Physiology or Medicine went to Victor Ambros and Gary Ruvkun for their discovery of microRNA, which helps determine how cells develop and function. 

The Nobel prize in chemistry will be awarded tomorrow.

A Short Demographic History Of Portugal

The Iberian Peninsula, located at the southwestern tip of Europe, is a geographically isolated region. Archaeological evidence indicates that this region has been occupied by humans for at least 400,000 years. It subsequently played a crucial role as a refuge during the Last Glacial Maximum. When the climate warmed about 14,000 years ago, people repopulated the European continent during the Mesolithic. The archaeological remains from this period in Portugal are characterized by the presence of numerous shell middens. Between 5700 and 5600 BC, the Neolithic brought a new way of life to the region with the introduction of agriculture and livestock. This development was brought about by human migrations from Anatolia. In particular, the maritime migrations of these groups brought to Portugal the ceramics of the Cardial culture that reached Portugal around 5500 BC. The latest paleogenomic studies have shown the arrival of a new population despite the persistence of a significant Mesolithic component. The improvement of technology and in particular the emergence of metallurgy resulted in more complex social organizations during the Chalcolithic between 3000 and 2000 BC. These societies are characterized by different regional cultures. In the Bronze Age, changes are observed from 2000 BC, characterized by the arrival of a steppe component in the genome of these ancient individuals. The Iron Age begins around 800 BC. The introduction of iron allows for major advances in agricultural methods, but also in warlike practices. The Celts are located in the north, west and center of the Iberian Peninsula. Phoenician trading posts appear in the southwest. The Roman conquest begins in 218 BC. when Portugal was integrated into the Roman Empire. This period saw the development of urbanization. Roman culture and the Latin language spread throughout the country. In the fifth century AD, Germanic tribes arrived in the Iberian Peninsula. The Suebi dominated the northwest until the unification of the peninsula by the Visigoths . At the beginning of the 8th century, Islamic tribes from North Africa invaded the peninsula, subsequently incorporating it into the Umayyad Caliphate . The Catholic reconquest culminated in the creation of the County of Portugal, then with the creation of the Kingdom of Portugal in 1143. In recent years, some paleogenomic studies have made it possible to study demographic movements during the history of the Iberian Peninsula, but only 51 ancient genomes dated before the Visigoth Kingdom have been analyzed in Portugal so far. 

Xavier Roca-Rada and his colleagues have just published a paper entitled:The genetic history of Portugal over the past 5,000 years . They sequenced 68 new ancient genomes from Portugal dated between the Neolithic and the 19th century. The authors added to these data 590 ancient genomes from the Iberian Peninsula previously published[.]

From here.

The demographic history of Portugal is complex and with old and new ancient DNA and lots of written history from a fairly early point, can be corroborated fairly accurately. It is easy to otherwise assume that an absence of evidence means that everything was simple, a lesson to be taken seriously in less well documented contexts.

New Moons Of Uranus and Neptune

Astronomers have found a new 7 km diameters moon of Uranus and new 14 km and 23 km moons around Neptune, which also shed light on the respective planet-moon-dust formation around these two planets. They believe that they have now detected all moons up to 8 km diameter around Uranus and up to 14 km around Neptune. But there are likely to be many undetected moons of up to 5 km diameter.

We have conducted extremely ultra-deep pencil beam observations for new satellites around both Uranus and Neptune. Tens of images on several different nights in 2021, 2022 and 2023 were obtained and shifted and added together to reach as faint as 26.9 and 27.2 magnitudes in the r-band around Uranus and Neptune, respectively. One new moon of Uranus, S/2023 U1, and two new moons of Neptune, S/2021 N1 and S/2002 N5, were found. 

S/2023 U1 was 26.6 mags, is about 7 km in diameter and has a distant, eccentric and inclined retrograde orbit similar to Caliban and Stephano, implying these satellites are fragments from a once larger parent satellite. S/2023 U1 almost completely overlaps Stephano in orbital phase space. 

S/2021 N1 was 26.9 mags, about 14 km in size and has a retrograde orbit similar to Neso and Psamathe, indicating they are a dynamical family. We find S/2021 N1 is in a Kozai-Lidov orbital resonance. 

S/2002 N5 was 25.9 mags, is about 23 km in size and it makes a family of distant prograde satellites with Sao and Laomedeia. 

All three new moons show for the first time dynamical groups of moons exist around both Uranus and Neptune. The creation of these groups likely produced dust that could be the source of red material seen on the leading hemispheres of some larger inner satellites like Titania, Oberon and Umbriel. 

We also detected all known outer moons of Uranus and Neptune on multiple nights. This survey mostly completes the outer satellites of Uranus to about 8 km and Neptune to about 14 km in diameter. 

The size distributions of satellite dynamical families around the giant planets shows a strong steepening in the power law size distribution smaller than 5 km in diameter. The satellites of a family become much more common smaller than 5 km and their size distribution is consistent with a collisional break-up of a once larger parent satellite.

Scott Sheppard, "New Moons of Uranus and Neptune from Ultra-Deep Pencil Beam Surveys" arXiv:2410.00108 (September 30, 2024) (Accepted Astronomical Journal).

Woit On What We Should Be Looking For

In a rare, insightful moment, Peter Woit offers his suggestions on where a deeper understanding of space-time and quantum gravity should be headed. I tend to agree with him.

The big problem with the supposedly now conventional view that spacetime needs to be replaced by something more fundamental that is completely different is of course: “replaced with what?”. A lot of attention is given to two general ideas. One is “holography”, the other Arkani-Hamed’s amplitudes program. But these are now very old ideas that show no signs of working as hoped. . . .

One lesson of the development of our best fundamental theory is that the new ideas that went into it were much the same ideas that mathematicians had been discovering as they worked at things from an independent direction. Our currently fundamental classical notion of spacetime is based on Riemannian geometry, which mathematicians first discovered decades before physicists found out the significance for physics of this geometry. If the new idea is that the concept of a “space” needs to be replaced by something deeper, mathematicians have by now a long history of investigating more and more sophisticated ways of thinking about what a “space” is. That theorists are on the road to a better replacement for “space” would be more plausible if they were going down one of the directions mathematicians have found fruitful, but I don’t see that happening at all.

To get more specific, the basic mathematical constructions that go into the Standard Model (connections, curvature, spinors, the Dirac operator, quantization) involve some of the deepest and most powerful concepts in modern mathematics. Progress should more likely come from a deeper understanding of these than from throwing them all out and starting with crude arguments about holograms, tensor networks, or some such.

To get very specific, we should be looking not at the geometry of arbitrary dimensions, but at the four dimensions that have worked so well, thinking of them in terms of the spinor geometry which is both more fundamental mathematically, and at the center of our successful theory of the world (all matter particles are described by spinors). One should take the success of the formalism of connections and curvature on principal bundles at describing fundamental forces as indicating that this is the right set of fundamental variables for describing the gravitational force. Taking spin into account, the right language for describing four-dimensional geometry is the principal bundle of spin-frames with its spin-connection and vierbein dynamical variables (one should probably think of vectors as the tensor product of more fundamental spinor variables).

What I’m suggesting here isn’t a new point of view, it has motivated a lot of work in the past (e.g. Ashtekar variables). I’m hoping that some new ideas I’m looking into about the relation between the theory in Euclidean and Minkowski signature will help overcome previous roadblocks. Whether this will work as I hope is to be seen, but I think it’s a much more plausible vision than that of any of the doomers.

From Peter Woit's blog "Not Even Wrong" on recent articles discussing the somewhat fringe notion getting attention of Space-Time unraveling.

CDF Was Wrong On The W Boson Mass

Matt Strassler took some time last week to note at his blog that the CDF recalculation of the W boson mass (which was 0.1% higher than other measurements and also much higher than the Standard Model prediction from other known physical constants, which seems modest but is a little more than eight standard deviations higher than the expected value) was wrong. 

The Standard Model electroweak fit from other physically measured constants (shown as the dashed line in the chart below) is as follows:

80,357 ± 4 [inputs] ± 4 [theory] MeV/c2

Since the ATLAS and CMS results are both consistent with all other previous measurements as well as with the Standard Model, and since CMS has even reached the same level of uncertainty obtained by CDF, this makes CDF by far the outlier, as you can see above. The tentative but reasonable conclusion is that the CDF measurement is not correct.

This was pretty much what everyone had suspected in April of 2022 when this CDF result was announced. The source of the error in the CDF measurement and reanalysis of data is still not entirely clear.

A Particle Data Group review article on the subject is here. The PDG world average doesn't yet include the 2024 experimental results.

Dingo Origins

The dingo came from East Asia via Melanesia.

the new study, published in Nature Scientific Reports, uses sophisticated 3D scanning and geometric morphometrics on ancient dingo specimens to show clearly that they are most similar to Japanese dogs, as well as the 'singing dogs' of New Guinea and the highland wild dog of Irian Jaya.

The remains studied were over 3,000 years old. 

From this source, citing:

Koungoulos, L.G., Hulme-Beaman, A., Fillios, M. et al., "Phenotypic diversity in early Australian dingoes revealed by traditional and 3D geometric morphometric analysis." Sci Rep (2024) DOI: 10.1038/s41598-024-65729-3

John Hawks Revisits Neanderthal Genetic Diversity

 

Tree of relationships of Pleistocene human ancestors including Neanderthal and Denisovan genomes. Recent human relationships based on Ragsdale and coworkers (2013). The Thorin genome (grouped together with the Forbes' Quarry skull) adds to the diversity of later Neanderthals. The diversity among these groups was still less than within modern African populations or among Denisovan populations.

John Hawks analyzes the implications of the new  "Thorin" genome from Gortte Mandrin and provides charts above in the process of putting the new ancient genome in context.

String Theory Still A Failure

An op-ed article in the New York Times notwithstanding, string theory is still a failure.

The claim is that if it hasn't been experimentally disproven, and it is mathematically beautiful, we should study it. But, of course, you can't experimentally disprove it, because there isn't even a version of it that is suggested at the one that actually explains our reality.

The near definitive ruling out of supersymmetry which most scholars see as a precondition for it and low energy approximation of it doesn't help. The dubiousness of a Majorana neutrino theory doesn't help either. Its reliance of theories that only work in an anti-de Sitter universe which we don't live in also fails to recommend it. And, its claimed need for ten or eleven dimensions, in a four dimensional world, has not found satisfactory solutions.

Woit further develops this theme.

Pre-Colombian New World Admixture In Ancient Easter Island Genomes

Polynesian people reached Easter Island around 1250 CE and were the first humans there. Europeans first reached the island in 1722 CE, at which time there were 1,500 to 3,000 people living there. European diseases, Europeans killing them, and Portuguese slave traders brought the Polynesian population down to a low point of 110 people some time after the 1860s. This paper's introduction suggested that as many as 15,000 people were living on the island on its pre-European peak, but later studies and this paper suggest that this peak population was greatly overestimated. The best fit to the genetic data shows a steady but slow population increase on the island after it was settled until European first contact, and the ecological collapse theory is rejected.

About 10% of Easter Island ancestry comes from pre-Columbian admixture with the indigenous peoples of the Americas as a result of admixture events in the time period from 1250-1430 CE, with a best fit timing in the late 1300s. This date also strongly favors admixture with indigenous Americans after, and not before the ancestors for the sampled individuals arrived on Easter Island. In particular, "the Native American component in Ancient Rapanui to be most closely related to Pacific Coast South Americans and not North Americans or populations east of the Andes further substantiates trans-Pacific contacts between Polynesians and Native Americans."

This further corroborates prior evidence of pre-Columbian contact between Polynesians and the pre-Columbian peoples of the Americas, and is also consistent the with expected time frame of these contacts from prior data.

we reconstructed the genomic history of the Rapanui on the basis of 15 ancient Rapanui individuals that we radiocarbon dated (1670–1950 CE) and whole-genome sequenced (0.4–25.6×). We find that these individuals are Polynesian in origin and most closely related to present-day Rapanui, a finding that will contribute to repatriation efforts. Through effective population size reconstructions and extensive population genetics simulations, we reject a scenario involving a severe population bottleneck during the 1600s, as proposed by the ecocide theory. Furthermore, the ancient and present-day Rapanui carry similar proportions of Native American admixture (about 10%). Using a Bayesian approach integrating genetic and radiocarbon dates, we estimate that this admixture event occurred about 1250–1430 CE.

From here. The body text of the article provides some background:

several pieces of evidence suggest that Rapa Nui did not constitute the easternmost point of long sea voyages and that Polynesian peoples eventually reached the Americas before Columbus. 

Genetic studies on present-day individuals have supported such contact. Present-day Rapanui were found to harbour Native American and European admixture in their genomes. Notably, in that work, Native American admixture (dated 1280–1495 CE) was estimated to pre-date European admixture (dated 1850–1895 CE). 

More recently, Native American admixture was detected not only in present-day individuals from Rapa Nui, but also from Rapa Iti, Tahiti, Palliser, Nuku Hiva (North Marquesas), Fatu Hiva (South Marquesas) and Mangareva. In that study, the Native American gene flow in the different islanders was dated between 1150 (South Marquesas) and 1380 CE (Rapa Nui), in line with the date estimated in ref. 5. 

However, the only two ancient DNA studies of ancient Rapanui so far did not find evidence for Native American admixture. The first study focused on mitochondrial DNA from 12 individuals, whereas the second analysed low-depth (0.0004–0.0041×) whole-genome data from 5 individuals dating before and after European contact. In the latter, downstream population genetic analyses confirmed that the five ancient individuals were Polynesian. However, even though the analysed human remains were post-dating the inferred Native American admixture time, no Native American ancestry was reported in these ancient genomes, casting doubt on the findings based on data from present-day populations.

The admixture and Native American contract dates cited above are also just in the right time frame to explain the geographic distribution and lack of fixation of "Paleo-Asian" ancestry in modern South American populations, although that scarce Paleo-Asian component is very small and is seemingly not a very close match to Polynesian ancestry. 

The geographic spread and lack of fixation of the Paleo-Asian component in South America is inconsistent and irreconcilable with a time depth greater than that of the primary founding population of the Americas for that genetic ancestry component.

Highlights From The Last Year In High Energy Physics

A new fourteen page preprint summarizing results from several of the main subjects discussed at the Moriond 2024 conference has a highly concentrated wealth of results from the last year, some of which were first announced at the conference. The paper is Barbara Clerbaux, "Experimental Summary of the Moriond 2024 conference - Electroweak Interaction & Unified Theories" arXiv:2409.07120 (September 11, 2024).

This year's results generally strongly vindicate the Standard Model of Particle Physics, although there are a few minor experimental tensions with it. I summarize the results further below.

The Higgs Boson

The latest (full run 2) mass measurement from CMS and from ATLAS are mH = 125.04 ± 0.11 (stat) ± 0.05 (syst) GeV for the H→ZZ→4ℓ decay channel and mH = 125.17 ± 0.11 (stat) ± 0.09 (syst) GeV for the H→γγ decay channel, respectively, the main uncertainties coming from the lepton and photon energy scales. Figure 1 presents the various H mass measurements of ATLAS and the final run 1 and run 2 combination, leading to a relative precision of 0.09%. The H mass uncertainty target for the HL-LHC is about 20 MeV. 

The tiny width predicted in the SM of 4.1 MeV is much smaller than the experimental mass resolution of about 1 to 2 GeV. However BSM contributions could bring a significant enhancement of the H width. ATLAS and CMS deduced an indirect limit on the H width using the ratio of the off-shell and on-shell cross section measurements. 

Various other measurements of Higgs boson decays and couplings are basically consistent with the Standard Model predictions for those properties.  

A wide scope of new BSM H boson searches has been released by ATLAS and CMS. No excess are observed above the SM prediction, however still a large amount of phase space is available for extended H sectors. In the search for low mass H→γγ, CMS observes an excess of local (global) significance of 2.9σ (1.3σ) at a mass of 95.4 GeV, ATLAS observes a local significance of 1.7σ at 95.4 GeV. 

The 95.4 GeV excess is not statistically significant globally, or in the combined CMS and ATLAS measurements. Notably, the bump that is observed is very close to the mass of the Z boson, which is 91.188(2) GeV plus the mass of the b quark which is 4.183(7) GeV (according the latest Particle Data Group estimate), the sum of which is 95.371(7) GeV, which to three significant digits is 95.4 GeV. 

Since a bb decay is the most common form of Higgs boson decay, and Z boson-photon decays are also possible, one possibility, for example, is that this bump represents the decays of a real and a virtual Higgs boson pair in which one of the b quark decay products and a photon are missed by the LHC detectors and misinterpreted in the subsequent analysis.

The Electroweak Precision Results

The W mass is extracted from the W boson transverse mass and pT distributions. The obtained value, mW = 80366.5 ± 15.9 MeV, has an impressive precision of less than 0.02%. The W mass result, shown in Figure 4 (left) is in good agreement with the SM and does not confirm the higher value of the W mass obtained in 2022 by the CDF data re-analysis measurement. The ATLAS analysis is also sensitive to the W width, measured to be ΓW =2202±47 MeV. ATLAS performed a comprehensive study of events with jets and large missing transverse energy (MET) in the final state, providing a measurement of the differential Z→ ν¯ ν cross section as a function of the Z boson pT. The W mass is also measured by LHCb with uncertainties that are anti-correlated to that of ATLAS and CMS. Using about a third of the available run 2 dataset, the value of mW = 80354±32 MeV is obtained by LHCb, with the target to have an expected statistical precision with the full run 2 dataset of about 14 MeV. . . . 

The sin2θℓ eff measurement is a CMS highlighted new result presented at the conference. The mixing angle sin2θℓ eff is a key parameter of the SM and is calculated using other precise experimental inputs to be sin2θℓeff(SM)=0.23155±0.00004. Up to now the most precise measurements come from LEP and SLD, and differ between each other by about 3σ. The new CMS analysis uses the Drell-Yan events with electron or muon pairs in the final state. In case of the electron channel, the very forward calorimeters up to a pseudorapidity value of |η| = 4.36 are added in the event selection, increasing significantly the measurement precision of the forward-backward asymmetry in the lepton decay angle. From this, a value of sin2 θℓ eff=0.23157±0.00031 is extracted, reaching a comparable precision as the LEP and SLD measurements, as shown in Figure 4 (right). . . .

The test of lepton flavour universality (LFU) in W decays is the highlighted new result by ATLAS. The analysis uses the top-quark pair events and compares the occurrence of W decays in the muon and the electron final states. To reduce as much as possible the systematics uncertainties, the ratio R = BR(W→µν)/ BR(W→eν) is measured and normalised to the corresponding ratio for the Z boson BR(Z→µµ)/ BR(Z→ee). The ratio R obtained is presented in Figure 5(left), the value is in agreement with 1 with a relative uncertainty of 0.45%. This is the most precise single measurement for this ratio to date and is also more precise than the previous PDG (particle data group) average. 

The photon-induced production of a pair of tau leptons is observed for the first time in proton-proton collisions by CMS at 5.3σ. . . . Modifying the tau lepton magnetic moment modifies the γγ → ττ cross section and modifies the pT and mass distributions of the signal. A very precise measurement of the tau lepton anomalous magnetic moment is extracted and presented in Figure 5(right), in good agreement with the expected SM value given as the dashed vertical line. The measurement does not show evidence for the presence of new physics that would modify its value. 

Top Quark Physics 

Measurements of top quark properties have been reported by ATLAS and CMS. . . . A new combination of the ATLAS and CMS top quark mass measurements leads to mt = 172.52 ± 0.14 (stat) ± 0.30 (syst) GeV, the dominant systematics uncertainty coming from the b-quark jet energy scale. . . . The ttZ+tWZ cross section measurement has a small tension with the SM prediction (being slightly above at a 2σ level). The new ATLAS result on the t¯ tγ production is in agreement with the SM. 

Quantum entanglement in top events are new results that generated excitement and discussion during the conference. ATLAS and CMS presented their latest analysis results from top-antitop events in the dilepton decay channels. Top-quark pairs at the LHC are mainly unpolarised, with their spins being strongly correlated. The spin information can be measured via the final state particle angular variables. The spin correlation depends on the mass of the top-antitop system mt¯t and on the angular variables. A system is considered as being in a quantum entanglement state if D < −1/3, where D is defined as the trace of the spin correlation matrix divided by 3. . .  .  entanglement is observed with > 5σ at low mt¯t. The CMS analysis shows in addition that when a t¯t bound state (toponium, a colour singlet pseudo-scalar state) is included in the simulation, the agreement between the measurement and the SM simulations improves in the threshold mass region.

Beyond The Standard Model Physics 

[N]o deviation from the SM expectation has been observed[.]

Flavor Physics

The LHCb and CMS experiments made measurements of CP violation in b quark and charm quark decays that increase the precision with which the CP violating parameter in the CKM matrix has been measured.

The LHCb and Belle/Belle II experiments looked at lepton flavor universality violations in semi-leptonic decays of b quarks to charm quarks, in results that put the global average measurement in mild tension with the Standard Model prediction of lepton flavor universality (at a 3.2 sigma level). The great spread of the experimental results, however, casts doubt on the meaningfulness of a global average measurement.

Belle/Belle II improved the accuracy with which the branching fractions of ten kinds of B meson decays and measured the branching fractions of four more kinds of B meson decays for the first time.  

BESIII mostly measured charmed hadron decays, improving the precision with which the CKM matrix element for charm to strange quark transition probability is known and examining the possibility of lepton flavor universality violations:

Using this measurement together with input from lattice QCD calculation, the CKM matrix element |Vcs| is determined with a precision of 1.4%. When combined with the tau decay channel analysis, the precision on |Vcs| value improves to 1.0%. Lepton flavour universality tests have also been performed in leponic and semi-leptonic decays of charm mesons. No violation was observed at the 1.5% precision level.

Neutrino Physics

Multiple experiments including NOvA, T2K, and Super-Kamiokande studied neutrino oscillation parameters. The precision of the measurement of the mass difference between the second and third neutrino mass eigenstates was improved. A normal mass ordering is favored, but only inconclusively. CP violation in neutrino oscillations has also been largely confirmed, but its magnitude has large uncertainties.

Efforts to detect neutrinoless double-beta (0νββ) at the CUORE and Legend experiments continued to come up empty, increasing the minimum half-life for neutrinoless double-beta decay. At CUORE:

The limit obtained for the half-live time of 130Te, based on data taken from 2017-2023 . . . is T1/2 0ν > 3.8 x 10^25 yr at 90% CL, which is the most stringent limit for the 130Te to date. The corresponding limit on the effective Majorana mass assuming a light Majorana neutrino-exchange is mββ < 70-240 meV. 

The Legend experiment using enriched germanium detector 76Ge has a . . . ultimate goal is to reach sensitivity for a half-life time of this nucleus beyond 10^28 years, corresponding to a neutrino effective mass measurement of about 18 meV.

Neutrinoless double beta decay, if discovered, would be strong evidence that the neutrino is a Majorana particle with Majorana mass, and would represent the first evidence of non-conservation of lepton number ever observed. But, given the increasing evidence that the neutrino masses are masses are very small, with the lightest neutrino mass probably well under 18 meV, we shouldn't expect to be able to detect neutrinoless double beta decay in the near to medium term, even if neutrinos do have Majorana mass.

The Faser experiment at the LHC has as its goal: 

to measure SM neutrino interaction cross sections at unexplored TeV energies, as well as to search for long-lived BSM particles (e.g. axion-like particles ALPs). . . . New results were presented on neutrino (νe and νµ) interaction cross sections. . . . This represents the first detection of νe at the LHC. Results on limits on ALPs were also shown for a luminosity of 57.7 fb−1, excluding uncovered parameter space (in the coupling and mass plane) significantly. . . . 

The present neutrino mass limit of 0.8 eV from the Katrin experiment was reminded and the future release of the neutrino mass limit with 0.5 eV sensitivity expected for mid-2024 was presented, together with the R&D for the Katrin++ project to reach the inverted ordering mass scale.

The Katrin result is now outdated as previously reported at this blog. The new limit is actually 0.45 eV.

An interesting (small) deficit of events was observed by the IceCube experiment in the muon antineutrino survival probability for atmospheric neutrinos, that can be fitted with the addition of a fourth neutrino family (the p-value for the null hypothesis is 3.1%). 

The potentially anomalous IceCube results have been credibly explained as the result of flawed modeling. See also this July 2024 paper reaching a contrary conclusion.

Dark Matter Searches

Searches for dark matter (DM) by the Lux-Zeplin experiment at the Sanford Underground Research Facility and by the PandaX experiment at the China Jinping Underground Laboratory were reported.

None of the experiments detected any dark matter and the parameter space excluded by these direct dark matter detection experiments was expanded.

Muon g-2

Updates on anomalous magnetic moment of the muon defined as aµ = (gµ −2)/2 were also discussed. It is a very sensitive variable to new physics, as the quantum effects arise from virtual particle contributions from all known and potentially unknown particles. The long-standing discrepancy between the experimental measurements and the theory predictions has been scrutinised during the conference. The Fermilab Muon g-2 experiment is providing improved measurements, currently at a precision of 0.2 ppm. A lot of efforts are dedicated to the SM calculation, and more specifically on the hadronic vacuum polarisation contribution. New results on lattice QCD have been presented and when taken into account, the SM prediction for aµ falls better in line with the experimental results. However these computations are complicated, and lattice QCD results from other groups are expected to be public soon. A discussion will then take place on the inclusion or not of these results in the official SM calculation.

As mentioned in previous posts on the determination of the SM prediction for muon g-2, it is actually pretty clear that the experimental results confirm the SM prediction, and that the previously anomaly was a result of inaccurate experimental data that was used to substitute for some particular difficult Lattice QCD calculations. 

The Voynich Manuscript Is Not A Hoax

Image via Wikipedia

A post at Language Log explains how multispectral imaging from ten years ago (which was just recently released due to the efforts of a determined blogger) reveal that the Voynich Manuscript, an illustrated vaguely alchemical and astrological handwritten tome in an indecipherable code, probably written around 1425 CE, is not a hoax or fake. 

Claimed efforts to decipher it have likewise flopped.

CODATA Physical Constants Updated

CODATA is one of the global standards for measurements of physical constants (fundamental and otherwise). The 2022 update is now available at arXiv with commentary on how the values were established.

The 2026 CODATA adjustment of the fundamental constants is the next regularly scheduled adjustment. Data being used in this adjustment is required to have been discussed in a publication preprint or a publication prior to 31 December 2026.

The muon g-2 discussion in the preprint is already outdated (in part by design, as it is only considering papers before December 31, 2022).

The Muon g-2 Issue In A Nutshell

The introduction of a new paper by authors who describe themselves by the first initials of their surnames (KNTW) nicely sums of the state of the efforts to compare experimental measurements of muon g-2 with predictions of its value using the Standard Model of Particle Physics.

The anomalous magnetic moment of the muon, aµ, and its potential for discovering new physics stand at a crossroads. The accuracy and precision of the Standard Model (SM) prediction, a(SM)µ, relies on resolving significant tensions in evaluations of the hadronic vacuum polarization (HVP) contributions, a(HVP)µ . Data-driven evaluations of the HVP using e+e− → hadrons cross section data as input result in a value for a(SM)µ that is ∼ 5σ below the most recent experimental measurement from the Muon g−2 Experiment at Fermilab, a(exp)µ. With an unprecedented 200 parts-per-billion (ppb) precision, confirmation of previous measurements, and final results (expected in 2025) projected to improve the experimental precision by another factor of two, the measurements of aµ appear to be on solid ground.<1> However, high-precision lattice QCD calculations (incorporating QED corrections) and the most recent experimental measurement of the dominant e+e− → π+π− cross section from the CMD-3 experiment result in independent, but consistent values for aHVP that are >4σ larger than previous data-driven evaluations. They therefore generate values for a(SM)µ that are consistent with a(exp)µ and support a no-new-physics scenario in the muon g−2, whilst leaving an unexplained discrepancy with the vast catalogue of previously measured hadronic cross section data. 

The KNT (now KNTW) data-driven determinations of a(HVP)µ are crucial inputs to previous and future community-approved predictions for a(SM)µ from the Muon g−2 Theory Initiative. With multiple, independent lattice QCD evaluations of a(HVP)µ becoming significantly competitive only in recent years, it was one of only a few data-driven HVP evaluations which exclusively formed the value for a(HVP) lattice QCD and updated data-driven evaluations, with KNTW being a key input to the latter. An alternative approach to determine a(HVP)µ by experimentally measuring the spacelike vacuum polarization is under preparation at the MUonE Experiment. 

The KNTW procedure for evaluating the total hadronic cross section and a(HVP)µ (plus other precision observables which depend on hadronic effects) is undergoing a major overhaul and modernization of the analysis framework. The aim of this revamp is to make use of sophisticated analysis tools, perform new evaluations of various contributions, incorporate handles in the analysis structure that result in flexible and robust ways to test various systematic effects, improve determinations of corresponding systematic uncertainties and ultimately produce a new state-of-the-art in the determination of these quantities. These changes will be described in detail in the next full KNTW update. 

Such future data-driven evaluations of a(HVP)µ depend largely on new experimentally measured hadronic cross section data, particularly for the π+π− final state. These require increased precision and a more robust understanding of higher-order radiative corrections, which are currently being studied in detail within the STRONG2020 program and The RadioMonteCarlow 2 Effort. Whilst a discussion of these improvements is outside the scope of this letter, such future results have been announced from the BaBar, Belle II, BESIII, CMD-3, KLOE and SND experiments within the next few years. These new measurements could either fundamentally adjust the previous data-driven evaluations of a(HVP)µ used in the SM prediction that exhibits the ∼ 5σ discrepancy with a(exp)µ. Future SM predictions are expected to incorporate both to bring them more in line with e.g. the recent CMD-3 π+π− measurement or make the current tensions even worse if new measurements confirm lower cross section values with increased precision. 

Importantly, and as will be discussed in the next section, analysis choices in how to use these data can produce significantly different results. With this being the case, the future of a(HVP)µ and a(SM)µ being so uncertain, and the crossroads in the current tensions ultimately suggesting either a discovery of new physics or a multi-method confirmation of the SM, analysis blinding for data-driven determinations of the HVP is now paramount. 

<1> Alternative future measurements of aµ are also planned at JPARC and PSI.

Unification In Physics Doesn't Work

This figure was the classic illustration of force unification, although it turns out that unification doesn't happen, even under SUSY, with the constraints of recent high precision coupling constant measurements.

Woit at his "Not Even Wrong" blog shares some slides he did for a podcast on grand unified theories of physics, which try to combine the three forces of the Standard Model into a facets of a single force, typically within a single Lie group, rather than the SU(3) x SU(2) x U(1) of the Standard Model. He explains that:

The main goal of the slides is to explain the failure of the general paradigm of unification that we have now lived with for 50 years, which involves adding a large number of extra degrees of freedom to the Standard Model. All examples of this paradigm fail due to two factors: 

• The lack of any experimental evidence for these new degrees of freedom.  

• Whatever you get from new symmetries carried by the extra degrees of freedom is lost by the fact that you have to introduce new ad hoc structure to explain why you don’t see them.

Afghanistan, Once Upon A Time

There was a Greek kingdom in Afghanistan and surrounding parts of Central Asia, called the Greco-Bactrian Kingdom, for roughly 136 years from 256 BCE until 120 BCE.