Cosmological signatures of decaying dark matter

Abstract

The decaying dark matter (DDM) scenario is a viable way of ionizing the Universe at high redshifts. We examine the constraints on this scenario due to the diffuse ultraviolet flux and Gunn–Peterson tests. The latter require the decaying particle's lifetime to be less than |$\sim10^{23}\ {\rm s}$|⁠. Observations of the diffuse UV flux along with a conservative estimate of its Galactic component require the DDM particle to have mass greater than 28.5 eV. With larger estimates of the Galactic contribution to the UV flux, the limit becomes |$m > 34.5\ {\rm eV}.$| We also point out a distinctive signature of DDM: a sharp drop in the infrared part of the spectrum.