Is A Neutrino Anomaly Due To Bad Nuclear Physics Modeling?

It is often the case that a seemingly anomalous result is due to flawed model for making a theoretical prediction of the expected value. The "Gallium anomaly" in neutrino physics might be among them. But a new paper argues that this isn't the problem. This would open the door to beyond the Standard Model neutrino physics (something that I still very much doubt).

The gallium anomaly, a 20% deficit in the measured νe captures on 71Ga, remains unexplained. A recent work [Phys. Rev. Lett. 137, 131805 (2026), arXiv:2512.20560] has proposed a solution based on the breakdown of the factorization of lepton and nuclear wavefunctions that underlies the prediction of the cross section, combined with ad hoc Gamow-Teller nuclear transition densities. 

We test this proposed solution with transition densities calculated within the nuclear shell model (NSM), normalized to the 71Ge electron-capture half-life and convolved with Dirac-Hartree-Fock-Slater electron wavefunctions. We explore several NSM interactions, bare and effective Gamow-Teller operators, as well as the impact of the valence space. In all cases, we obtain remarkably consistent NSM transition densities. Our factorized and nonfactorized cross sections agree, remaining 20% higher than the measured value. In addition, we use NSM single-nucleon transition densities as ansatz and find that solving the anomaly requires fine-tuned densities, with percent-level cancellations and an overall scale orders of magnitude larger than the calculated NSM ones. We conclude that the gallium anomaly is not solved when using realistic nuclear transition densities.

D. Castillo, D. Frycz, J. Menéndez, "Possible Solution to the Gallium Anomaly? Nuclear Transition Densities" arXiv:2611.09788 (November 6, 2026).

MOND and Galaxy Clusters

MOND doesn't work as well in galaxy clusters as it does in individual galaxies. But it is a great improvement over Newtonian gravity without dark matter, even there. And it is closer to the mark than previously assumed now that the amount of interstellar gas has been determined to be underestitimated. This suggests that a fairly modest tweak could make it work in galaxy clusters as well. 

First proposed by Milgrom in 1983 as an alternative to the standard Cold Dark Matter (CDM) paradigm, Modified Newtonian Dynamics (MOND) has gained renewed momentum in light of persistent non-detections of exotic dark matter particles and growing tensions facing CDM on galactic scales. While MOND perfectly reproduces galactic rotation curves, it encounters notable challenges in explaining the equilibrium of galaxy clusters. Although it reduces the overall dark matter budget in these massive systems, an unidentified mass component remains required. 

This paper investigates the hypothesis that this missing mass is baryonic: composed of non-radiating ordinary matter such as stellar remnants, gas too diffuse to initiate star formation, or compact, ultra-dense clouds of cold molecular gas with low volume filling factors. Using a sample of 106 clusters mapped in X-rays, emitted by the hot intra-cluster medium (ICM) composing most of the visible mass, we derive first the total mass within the Newtonian dynamics, assuming hydrostatic equilibrium and spherical symmetry. Then, with the modified Poisson equation, we reconstruct the spatial distribution of the invisible missing matter within the MOND framework. In the sample, the relaxed systems harboring cooling flows, known as cool-core clusters, have the highest peaks of dark missing mass. Its density profile reveals a pronounced central concentration bounded by a steep truncation immediately beyond a core radius of 20-30 kpc, confirming previous studies. 

MOND reduces the necessary dynamical mass by a factor of 4 to 10. The residual missing mass is proportional to the total gas mass, being roughly twice lower.

Francoise Combes, "Modified Newtonian Dynamics and galaxy clusters" arXiv:2611.08702 (November 5, 2026) (accepted in PNAS (Inaugural article)).

There Are A Lot Of Dark Matter Models Out There

There are more than six thousand dark matter models floating out there in theory space. This is a lot, but it is also eminently finite. So, it makes sense that AI is a good tool to use to start making sense of them. But AI is not terribly accurate (81%), even though, in this case, it didn't actually hallucinate any new models.

Of course, there is only one right answer (which isn't guaranteed to be any of the models proposed so far), and a large share of them are ruled out be existing evidence (of which the creators of many models weren't necessarily aware).

To use a dark-matter model one needs to know what defines it, which observables it affects, which codes and likelihoods evaluate it, and under what assumptions a published bound applies. That information is scattered across tens of thousands of papers. 

We present DarkMatterFM-Registry, a machine-readable registry of dark-matter models extracted from arXiv full texts by a staged large-language-model (LLM) pipeline: 6,145 structured model cards, validated against a seven-file JSON Schema suite, ranked by expected value for observational follow-up, and enriched for the top ~2,000 with observables, constraints, and theory-to-observable routes. 

Schema checks pass 97.8% of cards, and an LLM-judged accuracy study on a stratified card sample finds 81% of section verdicts correct, 18% partially correct, and none hallucinated. 

As a first application we turn the registry into a priority-weighted roadmap of 25 concrete projects the community could build. The roadmap is built by judging every computational step of every enriched model's theory-to-observable routes as available, partial, or missing, and aggregating the resulting typed gaps weighted by model priority. 

We find that what blocks the most high-priority models is not missing theory but missing shared infrastructure: model files for existing relic-abundance solvers, a general non-cold Boltzmann-code framework, reusable indirect-detection likelihoods, and a Lyman-α forest likelihood for non-cold dark matter (the largest gap for structure-formation probes). The model cards, schemas, roadmap, and ranking are released making the project reproducible and the cards available for the community.

Ioana A. Zelko, Jo Bovy, Nolan Koblischke, "DarkMatterFM-Registry: A Machine-Readable Registry of Dark-Matter Models Extracted from the arXiv Literature" arXiv:2611.08583 (November 5, 2026)  (Accepted at the Machine Learning and the Physical Sciences Workshop (ML4PS), NeurIPS 2026. Registry, schemas, and code: this https URL).

A New X17 Paper

I continue to be skeptical that an X17 particle exists. There is no sign of it at the LHC so far, and it has not been replicated at a different experiment from ATOMKI that has seen anomalies.

The ATOMKI anomalies motivate the possibility of a new particle, the X17, with a mass of 17 MeV and weak couplings to nuclei and electrons. Such a particle may be produced at the LHC, travel 480 m in the far-forward direction, and decay to e+e− in FASER. 

In this paper, previous FASER searches for dark photons and axion-like particles (ALPs) are combined and interpreted as searches for a candidate X17 particle, the protophobic vector boson. The searches use data collected from pp collisions at s√=13.6 TeV in LHC Run 3 from 2022 for the dark photon search and from 2022-2023 for the ALP search. 

No excess events are found above the expected background, and the combined null results exclude a previously-unconstrained "low-coupling window" with electron coupling 6 × 10^−5 < ϵe < 1.2 × 10^−4. A "high-coupling window" remains.

FASER Collaboration, "Constraints on a Long-Lived X17 Vector Boson with FASER" arXiv:2611.03904 (November 2, 2026).

Another preprint has more X17 constraint discussion here.