New constraints on the dark side of non-standard interactions from reactor neutrino scattering data
Peter B. Denton, Julia Gehrlein
Abstract
In neutrino oscillation physics, numerous exact degeneracies exist under the name LMA-Dark. These degeneracies make it impossible to determine the sign of $\mathrm{\ensuremath{\Delta}}{m}_{31}^{2}$, 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 ($\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$) by COHERENT already ruled out the LMA-Dark solution for new physics with mediators heavier than ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\sim}50\text{ }\text{ }\mathrm{MeV}$, while cosmological considerations disfavor these scenarios for mediators lighter than ${M}_{{Z}^{\ensuremath{'}}}\ensuremath{\sim}3\text{ }\text{ }\mathrm{MeV}$. Here we leverage new data from the Dresden-II experiment, which provides the strongest bounds on $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ with reactor neutrinos to date. We show that these data completely remove the degeneracies in the ${\ensuremath{\nu}}_{e}$ 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 ${\ensuremath{\nu}}_{e}$ sector, it can still be restored in the ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ sectors, or with very specific couplings to up and down quarks, and we speculate on a path forward.