A Unified Dark Matter Explanation for ${\mathbf{B}}^{+}\to {\mathbf{K}}^{+}\mathbf{\nu }\bar{\mathbf{\nu }}$ and the Super-Kamiokande Antineutrino Excess

Abstract

Recent results from Super-Kamiokande and Belle II have revealed intriguing excesses over Standard Model expectations. Super-Kamiokande observes a mild excess of ${\bar{\nu }}_e^{}$-like events near $20\mathrm{MeV}$, while Belle II reports a branching fraction for $B^{+}\to K^{+}\nu \bar{\nu }$ that exceeds the Standard Model prediction by approximately $2.7\sigma$. In this work, we study the simplest UV-complete complex scalar dark matter model with a gauged $\text{U}(1{)}_{{\text{L}}_{\mu }-{\text{L}}_{\tau }}^{}$ symmetry. We demonstrate that a light dark sector can simultaneously reproduce the observed dark matter relic density and accommodate both excesses within a unified framework.

Comments: 6 pages, 2 figures