Small-scale Cosmic Signatures of Feebly Interacting Massive Particles

Understand

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.