New limits on dark photons from solar emission and keV scale dark matter

TL;DR

This paper updates constraints on solar-emitted dark photons using recent XENON1T data, finds they do not explain the observed excess, but dark matter absorption of dark photons can fit the excess within astrophysical limits.

Contribution

It provides new bounds on dark photon emission from the Sun and demonstrates that dark matter absorption of dark photons can explain the XENON1T excess.

Findings

XENON1T data constrains solar dark photon emission more than stellar energy loss.

Dark photon absorption by dark matter can fit the XENON1T excess.

Solar emission of dark photons does not explain the XENON1T excess.

Abstract

We provide updates to the limits on solar emission of dark photons, or more generally any light vector particle coupled to the electron vector current. The recent 2019 and 2020 electronic recoil data from XENON1T now provides more stringent constraints on these models than stellar energy loss in the sub-keV mass region. We also show that solar emission of dark photons does not provide a good fit to the recent XENON1T excess in the 2-5 keV energy bins. In contrast, the absorption of 2-4 keV mass dark photons that saturate the local dark matter mass density does provide a good fit to the excess, for mixing angles in the range $\epsilon \in (4-12)\times 10^{-16}$, while satisfying astrophysical constraints. Similarly, other models utilizing the vector portal can fit the excess, including those with operators that directly couple the dark photon field strength to electron spin.