Dark matter velocity dispersion effects on CMB and matter power spectra

TL;DR

This paper investigates how dark matter particle velocity dispersion influences the cosmic microwave background and matter power spectra, revealing notable effects for non-thermal dark matter origins that mimic warm dark matter signatures.

Contribution

It introduces a modified CAMB code to analyze velocity dispersion effects, highlighting their impact on small-scale power spectrum cut-offs for non-thermal dark matter.

Findings

Velocity dispersion causes a cut-off in the matter power spectrum.

Cold dark matter from thermal processes shows negligible effects.

Non-thermal dark matter induces effects similar to warm dark matter.

Abstract

Effects of velocity dispersion of dark matter particles on the CMB TT power spectrum and on the matter linear power spectrum are investigated using a modified CAMB code. Cold dark matter originated from thermal equilibrium processes does not produce appreciable effects but this is not the case if particles have a non-thermal origin. A cut-off in the matter power spectrum at small scales, similar to that produced by warm dark matter or that produced in the late forming dark matter scenario, appears as a consequence of velocity dispersion effects, which act as a pressure perturbation.