This six page article is just a conference paper summary of a much more involved modified gravity theory and its implications. The abstract is silent on how well it handles galaxy cluster physics, which deviate (in a quite systemic way) from simple toy-model MOND theories, or the Hubble tension.
We propose an alternative scalar-tensor theory based on the Khronon scalar field labeling a family of space-like three-dimensional hypersurfaces. This theory leads to modified Newtonian dynamics (MOND) at galactic scales for stationary systems, recovers GR plus a cosmological constant in the strong field regime, and is in agreement with the standard cosmological model and the observed cosmic microwave background anisotropies.
Luc Blanchet, Constantinos Skordis, "Khronon-Tensor theory reproducing MOND and the cosmological model" arXiv:2507.00912 (July 1, 2025) (Contribution to the 2025 Gravitation session of the 59th Rencontres de Moriond).
A fuller explanation of the theory can be found here.
Another lengthy paper by P. S. Bhupal Dev et al., examines the constraints dark matter-neutrino interactions which are very strict.
We present a comprehensive analysis of the interactions of neutrinos with the dark sector within the simplified model framework. We first derive the exact analytic formulas for the differential scattering cross sections of neutrinos with scalar, fermion, and vector dark matter (DM) for light dark sector models with mediators of different types. We then implement the full catalog of constraints on the parameter space of the neutrino-DM and neutrino-mediator couplings and masses, including cosmological and astrophysical bounds coming from Big Bang Nucleosynthesis, Cosmic Microwave Background, DM and neutrino self-interactions, DM collisional damping, and astrophysical neutrino sources, as well as laboratory constraints from 3-body meson decays and invisible Z decays.
We find that most of the benchmarks in the DM mass-coupling plane adopted in previous studies to get an observable neutrino-DM interaction effect are actually ruled out by a combination of the above-mentioned constraints, especially the laboratory ones which are robust against astrophysical uncertainties and independent of the cosmological history.
To illustrate the consequences of our new results, we take the galactic supernova neutrinos in the MeV energy range as a concrete example and highlight the difficulties in finding any observable effect of neutrino-DM interactions.
Finally, we identify new benchmark points potentially promising for future observational prospects of the attenuation of the galactic supernova neutrino flux and comment on their implications for the detection prospects in future large-volume neutrino experiments such as JUNO, Hyper-K, and DUNE. We also comment on the ultraviolet-embedding of the effective neutrino-DM couplings.
the Dalitz decays of vector mesons. Recently, the BESIII collaboration measured the Dalitz decay D∗0→D0e+e−D∗0→D0e+e− for the first time and reported a 3.5σ3.5σ excess over the theoretical prediction based on the vector meson dominance (VMD) model.
ReplyDeleteany thought
Different QCD models produce quite different results.
ReplyDeleteVMD, in particular, has a hit and miss record, with some interactions predicted right on the nose, and others, wildly off. A VMD calculation is a perturbative QCD simplification of full QCD (simplified for ease of computation). VMD is one of the older methods of simplifying full QCD to make it computationally tractable. But, the conditions under which it works better and the conditions under which it works less well are not terribly well understood.
Any gap between prediction and theory is very likely due to the inadequacies of the VWD methodology of approximating true and complete QCD. I'd take it more seriously if a good Lattice QCD study made the same prediction - but a Lattice QCD calculation is much, much more computationally intensive and much more work for the physicist doing it, than a VMD calculation.
Honestly, the extent to which QCD calculations are art as well as science, and the extent to which different approximations of QCD produce different results, is one of the "dirty little secrets" of high energy physics. At times, QCD and the SM can be remarkably precise. And, to get to 3.5 sigma, you still have to a prediction that is order of magnitude correct, so using a computationally efficient method to get reasonable close may still be "good enough for government work" in some circumstances.
ReplyDeleteOne of the interesting things about searches for new physics in HEP is that even though QCD is by a very long shot vastly less precise in what it can predict than electroweak physics, the are all sorts of proposals for new electroweak physics beyond the Standard Model, chasing the slightest and most short lived anomalies even after those anomalies are very nearly ruled out, while there are essentially no serious proposals to modify the SM version of QCD, where there is naively vast room in terms of experimental results and low precision for alternatives.
To some extent, that is because QCD, with its three quark colors, one coupling constant, one magnitude of color charge, and eight color combinations of gluons that are massless, is really quite an elegant theory with few moving parts. Progress in Lattice QCD in particular, that picks up non-perturbative QCD effects, has also tended to validate it and increase faith in it. And, perhaps the fact that the implementation of QCD is profoundly more difficult than EW physics has keep idle minds busy trying to implement orthodox QCD without modification, while EW physicists can't make their mark implementing it so they have to find something else to do like speculating about BSM modifications to it.