Gallium Anomaly Solved Without New Physics

The gallium anomaly as a 20% deviation from the expected number of neutrino interactions with a gallium atom, which was pointed at as evidence of sterile neutrinos. Only, it turns out that what was wrong was a 20% error in the calculation of the theoretically expected value by ignoring parts of the calculation that were too important to ignore. When calculated correctly, theory and experiment were consistent (in what has become, by now, a familiar pattern).

For more than 30 years, scientists have found that roughly 20% fewer electron neutrinos are captured by gallium nuclei than expected. Dubbed the gallium anomaly, this discrepancy has raised the possibility that something fundamental might be missing from our understanding of neutrinos or atomic nuclei. Now Matteo Cadeddu at the National Institute for Nuclear Physics (INFN) and the University of Cagliari, both in Italy, and his colleagues have shown that this mismatch may instead originate from the way the electron-neutrino capture rate is calculated [1]. . . . 

When an electron neutrino is captured by a gallium nucleus, an electron is created and a neutron turns into a proton, transforming gallium into germanium. In the standard capture-rate calculation, the behavior of the nucleus is treated separately from that of the neutrino and electron. This approximation simplifies the calculation but may overlook key aspects of the capture process. Cadeddu and his colleagues instead developed a more rigorous approach that fully accounts for the interplay between the nucleus, neutrino, and electron. Using this technique, the researchers predicted a capture rate about 20% lower than previous estimates, closely matching the experimental results. This finding offers a solution to the gallium anomaly without requiring new physics. It disfavors one of the previously leading explanations: the existence of so-called sterile neutrinos. . . . 

[1] M. Cadeddu, et al., "Possible solution to the gallium anomaly moving beyond the leptonic wave-function factoriziation," 137 Phys. Rev. Lett. 131805 (September 24, 2026). 

From here.

Are Neutrinos Really Massive? (And Top Quark Mass Technicalities)

Neutrino oscillation is the primary evidence for the conclusion that neutrinos have mass. And, this paradigm has been pretty successful so far (although, with six degrees of freedom, fitting the data isn't necessary too difficult). The short (five page) paper below makes the provocative argument that neutrino oscillation arises from the curvature of space-time rather than from massive neutrinos.

This would solve the problem of how neutrinos acquire mass, which is a major unsolved problem in physics, in an unexpected way: they don't. I'm skeptical, and this isn't a fully worked out idea that explains neutrino oscillation in full yet. But it is at least notable and deserves serious exploration by other researchers to see if this idea really has merit.

The Dirac equation in stationary curved spacetime implies that describing two-flavor neutrino oscillations requires treating the invariant mass and conserved energy of each propagating state distinctly, as gravity affects energy differently than mass. 

By re-analysing the publicly released KamLAND dataset, we show that modeling flavor states of massless neutrinos as two-level quantum states with energy-dependent level splitting, analogous to modified Jaynes-Cummings models, results in a higher-likelihood fit to the observed data than the standard massive-neutrino paradigm.

Golam Mortuza Hossain, Pushpit Kumar, "Neutrino Oscillations without Mass: A Re-analysis of KamLAND Data following the Dirac Equation in Curved Spacetime" arXiv:2609.39638 (September 30, 2026).

In other physics news, a preprint suggests corrections to the formula used to determine the top quark mass in one of the approaches used to do so (the introduction to the paper is also a good background discussion of the general issue addressed):

We calculate the three-loop O(αα2s) mixed QCD-EW corrections to the top quark mass and obtain the relationships between the pole (Mt) and MS bar (mt(μ)) masses at this order. 

In performing our calculation, we express the three-loop self-energies as a function of three-loop master integrals (MIs). These MIs are defined so as to solve a differential equation in ϵ-factorized form, allowing for their solution to be expressed as iterated integrals. We discuss the types of differential forms that we encounter, which include periods of elliptic curves, and their role in the final physical result. 

Using our results, we calculate the shift in mt(Mt) arising at this order. For Mt = 172.3 GeV, the shift is -216 MeV, which is comparable to the currently quoted experimental uncertainty.

Daniele Gaggero, Ciaran Williams, "O(αα2s) corrections to the Top Quark mass" arXiv:2609.40229 (September 30, 2026).