Feebly Interacting $U(1)_{\rm B-L}$ Gauge Boson Warm Dark Matter and XENON1T Anomaly

TL;DR

This paper proposes that a feebly interacting $U(1)_{B-L}$ gauge boson with keV-scale mass can serve as warm dark matter, explaining the XENON1T anomaly and addressing small-scale structure issues in cosmology.

Contribution

It introduces a non-thermal production mechanism for the $U(1)_{B-L}$ gauge boson as warm dark matter, linking it to the XENON1T excess and early universe physics.

Findings

The $U(1)_{B-L}$ gauge boson can explain the XENON1T excess with a kinetic mixing of ~10^{-15}.

The scenario addresses small-scale structure problems in cosmology.

The non-thermal origin involves decay of a coherently oscillating scalar field.

Abstract

The recent observation of an excess in the electronic recoil data by the XENON1T detector has drawn many attentions as a potential hint for an extension of the Standard Model (SM). Absorption of a vector boson with the mass of $m_{A'}\!\in\!(2\,{\rm keV},\!3\,{\rm keV})$ is one of the feasible explanations to the excess. In the case where the vector boson explains the dark matter (DM) population today, it is highly probable that the vector boson belongs to a class of the warm dark matter (WDM) due to its suspected mass regime. In such a scenario, providing a good fit for the excess, the kinetic mixing $\kappa\!\sim\!10^{-15}$ asks for a non-thermal origin of the vector DM. In this letter, we consider a scenario where the gauge boson is nothing but the $U(1)_{\rm B-L}$ gauge boson and its non-thermal origin is attributed to the decay of the coherently oscillating scalar of which condensation induces the spontaneous breaking of $U(1)_{\rm B-L}$. We discuss implications for the early universe physics when the warm nature of the vector DM serves as a resolution to both the small scale problems that $\Lambda$CDM model encounters and the XENON1T anomaly.