Small-scale Cosmic Signatures of Feebly Interacting Massive Particles

TL;DR

This paper investigates the potential small-scale cosmic signatures of Feebly Interacting Massive Particles (FIMPs), deriving bounds and analyzing their impact on structure formation to address challenges in standard cosmological models.

Contribution

It introduces an analytic approximation for FIMP phase-space distribution and explores viable theories that resolve small-scale structure issues in cosmology.

Findings

Derived bounds for feeble theories based on small-scale structure signatures

Identified FIMP models compatible with standard cosmological evolution

Provided a framework to constrain FIMPs through cosmic structure observations

Abstract

Feebly Interacting Massive Particles (FIMPs), if they exist, should be notoriously difficult to detect even indirectly. In order to constrain them, we derive bounds for feeble theories sourced via Standard Model fields by investigating their predicted signatures regarding small-scale structure formation. To achieve this, we obtain an analytic approximation for the phase-space distribution function for a generic dimension $\ell$ scattering operator. As a proof of concept, realizations of such theories are discussed, which provide a viable thermal evolution and are able to solidly solve the enduring small-scale structure challenges appearing in $\Lambda$CDM cosmology.