Constraints on freeze-in dark matter from Lyman-$\alpha$ forest and 21-cm signal : single-field models

TL;DR

This paper uses Lyman-alpha and 21-cm observations to set new constraints on freeze-in dark matter models, particularly sterile neutrinos and millicharged particles, refining their allowed parameter space.

Contribution

It provides the first combined analysis of Lyman-alpha and 21-cm data to constrain freeze-in dark matter, including future sensitivity projections for SKA-low.

Findings

Lyman-alpha data excludes sterile neutrino FIDM masses above 1.8×10^{-3} GeV.

Future 21-cm observations could exclude sterile neutrino FIDM masses above 5.46×10^{-4} GeV.

Current Lyman-alpha data only weakly constrains millicharged FIDM, leaving much of the parameter space open.

Abstract

We report new Lyman-$\alpha$ and 21-cm constraints on freeze-in dark matter (FIDM) which injects energy into the intergalactic medium either through annihilation or decay to photon(s) or electron-positron pair. With respect to Lyman-$\alpha$ we fix the baseline ionization history using low redshift data about astrophysical reionization, whereas for 21-cm signal we adopt the baseline values of 21-cm power spectrum through a standard modeling of star formation developed so far. Using the latest numerical tools, we show that (i) for sterile neutrino FIDM, current Lyman-$\alpha$ data and future sensitivity of SKA-low (1000 hrs) on the 21-cm power spectra excludes the FIDM mass up to $1.8\times 10^{-3}$ GeV at 95$\%$ CL and $5.46\times 10^{-4}$ GeV, respectively, and (ii) for millicharged FIDM, current Lyman-$\alpha$ data only excludes the millicharge down to $10^{-8}$ within the FIDM mass range of $10^{-3}-1$ GeV at 95$\%$ CL, suggesting that the surviving parameter space of millicharged FIDM is still intact.