Massive hidden photons as lukewarm dark matter

TL;DR

This paper investigates whether keV-MeV mass hidden photons, interacting via kinetic mixing, can account for dark matter, but finds they are likely only a subdominant component due to astrophysical and cosmological constraints.

Contribution

It provides a detailed calculation of hidden photon relic abundance including plasma effects and assesses observational bounds, concluding the viability of hidden photons as dominant dark matter is limited.

Findings

Hidden photons can only contribute subdominantly to dark matter.

Resonant production is almost independent of hidden photon mass.

Astrophysical and cosmological bounds strongly constrain hidden photon dark matter.

Abstract

We study the possibility that a keV-MeV mass hidden photon (HP), i.e. a hidden sector U(1) gauge boson, accounts for the observed amount of dark matter. We focus on the case where the HP interacts with the standard model sector only through kinetic mixing with the photon. The relic abundance is computed including all relevant plasma effects into the photon's self-energy, which leads to a resonant yield almost independent of the HP mass. The HP can decay into three photons. Moreover, if light enough it can be copiously produced in stars. Including bounds from cosmic photon backgrounds and stellar evolution, we find that the hidden photon can only give a subdominant contribution to the dark matter. This negative conclusion may be avoided if another production mechanism besides kinetic mixing is operative.