A New Anomaly

There are four sets of valence quarks that produce kaons, two of which are charged and two of which are electromagnetically neutral: 

K⁺ (positive charge: up quark + anti-strange quark)

K⁻ (negative charge: anti-up quark + strange quark)

K⁰ (neutral: down quark + anti-strange quark)

K̄⁰ (neutral antiparticle: anti-down quark + strange quark)

In certain heavier atom collisions, there are more charged kaons than expected relative to the number of neutral kaons observed, which means that there are more up quarks (and anti-up quarks) relative to down quarks (and anti-down quarks) than expected.

Isospin symmetry is the concept that particles with up quarks substituted for down quarks (and vice versa) are identical in strong force interactions (in part, due to their similar mass and the indifference of the strong force to electromagnetic or weak force charge).

For some reason, however, more charged kaons are seen in argon-scandium collisions and also in some other particle collisions. The paper below fails to come up with a good explanation for why this is the case and calls for further study. The introduction to the paper explains that:

This paper focuses on hadron–nucleus and nucleus–nucleus collisions at center-of-mass (cms) energies of the order of 10 GeV per nucleon pair. Such processes are governed by (mostly) non-perturbative strong interactions, and result in the production of a large number– tens, hundreds– of new particles in the final state (multiparticle production). 

Isospin symmetry (IS) which can be considered as a remnant of the QCD flavor symmetry between u and d quarks, remains an essential even if approximate feature of the production process. 

At energies equal (or higher) to those specified above, the bulk features of multiparticle production (inclusive spectra, total multiplicities, etc) are widely believed to obey IS up to a very good accuracy, of the order of 3−4%. Nevertheless, the simultaneous measurement of inclusive spectra and yields of charged (K+, K−) and neutral (K0 S) mesons reported by the NA61/SHINE experiment in central Ar+Sc collisions at √ sNN = 11.9 GeV [1] reveals an unexpectedly large IS violation (18 ±6% at kaon mid-rapidity). 

As will be discussed below, measurements from other experiments over a wide range of collision energy appear consistent with this observation. At the present moment (Oct., 2026), the origin of this effect remains unclear.

The paper and its abstract are as follows: 

The NA61/SHINE experiment at the CERN SPS reports an unexpectedly large excess in the inclusive production of charged over neutral kaons in 0-10% central Ar+Sc collisions at sNN‾‾‾‾√=8.8 and 11.9 GeV. This effect corresponds to an unexpectedly large violation of isospin symmetry, that cannot be explained by known mechanisms contained in the present theoretical models. 

The comparison of the NA61/SHINE results to data from other experiments reveals, within sizeable uncertainties, a consistent isospin symmetry-violating excess of charged kaon production in the energy regime 2.6<sNN‾‾‾‾√<200 GeV. At LHC energies (0.9<sNN‾‾‾‾√<13 TeV) the charged-over-neutral kaon ratio appears consistent with unity, but the uncertainties remain sizeable. 

A similar excess of charged over neutral kaon yields is observed by NA61/SHINE in minimum bias π−+C reactions at sNN‾‾‾‾√=17.3 and 25.7 GeV, also in disagreement with model predictions. 

No clear theoretical explanation of these phenomena has been provided so far. An unexpectedly large violation of isospin symmetry brings potential heavy consequences for our understanding of particle production, and calls for a concentrated experimental and theoretical effort.

Andrzej Rybicki for the NA61/SHINE Collaboration, "Unexpectedly large violation of isospin symmetry in nucleus-nucleus collisions at CERN SPS energies" arXiv:2610.23498 (October 16, 2026) (18th International Workshop on Meson Physics (MESON 2026), Kraków, Poland).

I'm personally confident that ultimately an explanation consistent with Standard Model physics will be found. But it is a fairly recent anomaly that hasn't gotten a lot of attention yet, so it deserves a post here.

Milgrom's Latest MOND Paper

Mordehai Milgrom, who invented MOND, has long been ambivalent about whether this is really a modification of gravity or a modification of inertia. In his latest paper, he considers the possibility that it could be both.

It is plausible that in a more fundamental theory of MOND both gravity and inertia will differ from their Newtonian versions. Such theories, if they embody the basic tenets of MOND, will share its primary predictions with existing theories, which modify either gravity or inertia. But they are expected to differ in their structure and in their secondary predictions. 

Here, I discuss families of nonrelativistic MOND theories that modify both the kinetic and the gravitational actions of Newtonian dynamics. Each family is spanned by one parameter 0≤η≤1, which is the scaling dimension of the deep-MOND limit of all terms in the action. Pure modified gravity (η=0) and pure modified inertia (η=1) are the end cases in each family. I speak of families, since the modified action terms themselves are not strictly specified, but are treated in rather general terms. 

These theories are artificial in that they are not based on a single unifying idea that dictates the modification of the two components. But they are still useful in pinpointing some idiosyncracies of such theories. 

For example, neither of the two modified terms, by itself, leads to MOND phenomenology; only their combined effect does. I show how the two combine to make some of the primary MOND predictions, such as asymptotic flatness of rotation curves, the mass-asymptotic-speed relation, and the deep-MOND, virial, mass-velocity-dispersion (M−σ) relation. 

Another idiosyncracy of such theories is the emergence of different interpolating functions in the kinetic equations of motion and in the gravitational field equations, each relevant under different circumstances, and neither of which have the standard deep-MOND limit. Such examples alert us to the wide range of theories that can lead to MOND phenomenology.

Mordehai Milgrom, "Mixed modified-gravity--modified-inertia MOND theories" arXiv:2610.21699 (October 15, 2026).

Gallium Non-Anomaly Confirmed

The Gallium Anomaly had been used to support the idea of sterile neutrinos. But it turns out that the anomaly was just a result of a flawed calculation of the Standard Model expectation. The correct calculation shows no anomaly in independent experimental measurements.

The Gallium Anomaly is the disagreement between the measured capture rate of neutrinos by 71Ga and the rate theoretically expected from the electron capture decay of 71Ge. The experimental measurements were performed with intense artificial sources. 

In the present work we consider the sun as a neutrino source that can be calibrated via the fundamental, standard-model neutrino-electron elastic scattering reaction in terrestrial detectors. The result is found to be not anomalous, with good agreement between the measured value of 66.1 ± 3.1 SNU from SAGE and Gallex/GNO, and the total measured source strengths of solar sources, 67.5 +1.4 −1.1 SNU. It may be concluded that neither the 71Ga charged-current cross section nor gallium experiment extraction and counting efficiencies account for the Gallium Anomaly.

Steven R. Elliott, R. G. Hamish Robertson, "Gallium Anomaly and Solar Neutrinos"arXiv:2610.22219 (October 15, 2026).

Another paper confirms again that muon g-2 doesn't show a discrepancy between theoretical predictions of it and experimental measurements of it at extreme precision. The muon g-2 anomaly was also due to a flawed calculation of the Standard Model expectation. 

Progress is also being made in the tau g-2 calculation, but the experimental measurements of tau g-2 are too imprecise to meaningfully compare them to the theoretical calculation.