Lower Mass Bounds on FIMP Dark Matter Produced via Freeze-In

TL;DR

This paper establishes lower mass bounds for FIMP dark matter produced via freeze-in, analyzing different production mechanisms and their impact on structure formation, with implications for sub-dominant dark matter scenarios.

Contribution

It provides a model-independent analysis of FIMP production mechanisms and derives lower mass bounds based on cosmological structure suppression.

Findings

Lower bounds on FIMP mass from structure formation constraints

Analysis of decay and collision production mechanisms

Implications for sub-dominant dark matter scenarios

Abstract

Feebly Interacting Massive Particles (FIMPs) are dark matter candidates that never thermalize in the early universe and whose production takes place via decays and/or scatterings of thermal bath particles. If FIMPs interactions with the thermal bath are renormalizable, a scenario which is known as freeze-in, production is most efficient at temperatures around the mass of the bath particles and insensitive to unknown physics at high temperatures. Working in a model-independent fashion, we consider three different production mechanisms: two-body decays, three-body decays, and binary collisions. We compute the FIMP phase space distribution and matter power spectrum, and we investigate the suppression of cosmological structures at small scales. Our results are lower bounds on the FIMP mass. Finally, we study how to relax these constraints in scenarios where FIMPs provide a sub-dominant dark matter component.