Warm and cold fermionic dark matter via freeze-in

TL;DR

This paper investigates the freeze-in mechanism for fermionic dark matter within a simple singlet model, showing it can produce both warm and cold dark matter over a wide mass range, including below keV.

Contribution

It demonstrates that freeze-in can account for dark matter in a minimal singlet fermionic model, allowing for a broad mass spectrum and bypassing WIMP unitarity bounds.

Findings

Dark matter abundance explained via freeze-in across a wide mass range.

Both warm and cold dark matter scenarios are achievable.

Dark matter masses can exceed WIMP unitarity bounds.

Abstract

The freeze-in mechanism of dark matter production provides a simple and intriguing alternative to the WIMP paradigm. In this paper, we analyze whether freeze-in can be used to account for the dark matter in the so-called singlet fermionic model. In it, the SM is extended with only two additional fields, a singlet scalar that mixes with the Higgs boson, and the dark matter particle, a fermion assumed to be odd under a Z_2 symmetry. After numerically studying the generation of dark matter, we analyze the dependence of the relic density with respect to all the free parameters of the model. These results are then used to obtain the regions of the parameter space that are compatible with the dark matter constraint. We demonstrate that the observed dark matter abundance can be explained via freeze-in over a wide range of masses extending down to the keV range. As a result, warm and cold dark matter can be obtained in this model. It is also possible to have dark matter masses well above the unitarity bound for WIMPs.