Relic Abundance of Dark Photon Dark Matter

Abstract

We present a new mechanism for producing the correct relic abundance of dark photon dark matter over a wide range of its mass, extending down to $10^{-20}\mathrm{eV}$. The dark matter abundance is initially stored in an axion which is misaligned from its minimum. When the axion starts oscillating, it efficiently transfers its energy into dark photons via a tachyonic instability. If the dark photon mass is within a few orders of magnitude of the axion mass, $m_{{\gamma }^{\prime }}/m_a=\mathcal{O}(10^{-3}-1)$, then dark photons make up the dominant form of dark matter today. We present a numerical lattice simulation for a benchmark model that explicitly realizes our mechanism. This mechanism firms up the motivation for a number of experiments searching for dark photon dark matter.

Comments: 5 pages + supplementary material, 4 figures