Matter Power Spectrum in Hidden Neutrino Interacting Dark Matter Models: A Closer Look at the Collision Term

TL;DR

This paper investigates how hidden neutrino interactions with dark matter affect the matter power spectrum, introducing a new derivation of the collision term and emphasizing the role of vector and scalar mediators in addressing small-scale structure issues.

Contribution

It provides a first-principles derivation of a generalized Fokker-Planck equation for cosmological perturbations and introduces a broadly applicable collision term with phenomenological implications.

Findings

Suppressed matter power spectrum on subgalactic scales.

Vector and scalar boson mediators are equally important.

New gauge-invariant derivation of perturbation equations.

Abstract

Dark Matter (DM) models providing possible alternative solutions to the small- scale crisis of standard cosmology are nowadays of growing interest. We consider DM interacting with light hidden fermions via well motivated fundamental operators showing the resultant matter power spectrum is suppressed on subgalactic scales within a plausible parameter region. Our basic description of the evolution of cosmological perturbations relies on a fully consistent first principles derivation of a perturbed Fokker-Planck type equation, generalizing existing literature. The cosmological perturbation of the Fokker-Planck equation is presented for the first time in two different gauges, where the results transform into each other according to the rules of gauge transformation. Furthermore, our focus lies on a derivation of a broadly applicable and easily computable collision term showing important phenomenological differences to other existing approximations. As one of the main results and concerning the small-scale crisis, we show the equal importance of vector and scalar boson mediated interactions between DM and light fermions.