Dark Matter Interpretation of the Super-Kamiokande Antineutrino Excess in $\mathrm{U}(1{)}_{L_{\mu }-L_{\tau }}$ model

Abstract

Recent Super-Kamiokande analyses of the diffuse supernova neutrino background, based on data across all SK phases, indicate a mild preference over the zero-DSNB hypothesis at the level of about $2.3\sigma$ with electron-like antineutrino events at $E_{{\bar{\nu }}_e}\simeq 20\mathrm{MeV}$. We investigate whether this excess can be explained by MeV-scale dark matter annihilation into neutrinos in a $\mathrm{U}(1{)}_{L_{\mu }-L_{\tau }}$ model. The dark matter is a Dirac fermion with $m_{\chi }\simeq 22\mathrm{MeV}$ that annihilates via a light $Z^{\prime }$ mediator into ${\nu }_{\mu }{\bar{\nu }}_{\mu }$ and ${\nu }_{\tau }{\bar{\nu }}_{\tau }$, which are partly converted into ${\bar{\nu }}_e$ through flavor oscillations. We find that this scenario simultaneously accounts for the excess and the observed relic abundance via thermal freeze-out. We further discuss the relevant laboratory and cosmological constraints, including neutrino trident production, NA64-$\mu$, Borexino, and the contribution to $\Delta N_{\mathrm{eff}}$.

Comments: 9 pages, 2 figures