New constraints on the dark side of non-standard interactions from reactor neutrino scattering data

In neutrino oscillation physics, numerous exact degeneracies exist under the name LMA-Dark. These degeneracies make it impossible to determine the sign of.Delta m(31)(2),known as the atmospheric mass ordering, with oscillation experiments alone in the presence of new neutrino interactions. The combination of different measurements, including multiple oscillation channels and neutrino scattering experiments, lifts some aspects of these degeneracies. In fact, previous measurements of coherent elastic neutrino nucleus scattering (CE nu NS) by COHERENT already ruled out the LMA-Dark solution for new physics with mediators heavier than M-Z' similar to 50 MeV, while cosmological considerations disfavor these scenarios for mediators lighter than M-Z' similar to 3 MeV. Here we leverage new data from the Dresden-II experiment, which provides the strongest bounds on CE nu NS with reactor neutrinos to date. We show that these data completely remove the degeneracies in the nu(e) sector for mediators down to the MeV scale, at which point constraints from the early Universe take over. While the LMA-Dark degeneracy is lifted in the nu(e) sector, it can still be restored in the nu(mu) and.nu(iota) sectors, or with very specific couplings to up and down quarks, and we speculate on a path forward.

Automated summary

This article mainly introduces the degeneracies in neutrino oscillation physics, known as LMA-Dark, which make it impossible to determine the atmospheric mass ordering using oscillation experiments alone. By combining different measurements, the degeneracies can be lifted to some extent. New data from the Dresden-II experiment are used to completely remove the degeneracies in the ν(e) sector at the MeV scale. However, the LMA-Dark degeneracy can still be restored in the ν(μ) and ν(τ) sectors.