Hints of dark photon dark matter from observations and hydrodynamical simulations of the low-redshift Lyman-$\alpha$ forest

Abstract

Recent work has suggested that an additional $\lesssim 6.9\mathrm{eV}$ per baryon of heating in the intergalactic medium is needed to reconcile hydrodynamical simulations with Lyman-$\alpha$ forest absorption line widths at redshift $z\simeq 0.1$. Resonant conversion of dark photon dark matter into low frequency photons is a viable source of such heating. We perform the first hydrodynamical simulations including dark photon heating and show that dark photons with mass $m_{A^{\prime }}\sim 8\times 10^{-14}\mathrm{eV}{\mathrm{c}}^{-2}$ and kinetic mixing $ϵ\sim 5\times 10^{-15}$ can alleviate the heating excess. A prediction of this model is a non-standard thermal history for underdense gas at $z\gtrsim 3$.

Comments: 5+1 pages, 2+1 figures