WIMP isocurvature perturbation and small scale structure

TL;DR

This paper investigates how isocurvature perturbations in WIMP dark matter, unaffected by damping during kinetic decoupling, can significantly influence small scale structure formation, especially during early matter domination.

Contribution

It demonstrates that isocurvature perturbations generated during phase transitions can impact small scale structures, a novel insight into dark matter's role in cosmic evolution.

Findings

Isocurvature perturbations can be large and influence small scale structures.

Early matter domination enhances isocurvature effects.

Observable signatures in small scale structure are linked to phase transition processes.

Abstract

The adiabatic perturbation of dark matter is damped during the kinetic decoupling due to the collision with relativistic component on sub-horizon scales. However the isocurvature part is free from damping and could be large enough to make a substantial contribution to the formation of small scale structure. We explicitly study the weakly interacting massive particles as dark matter with an early mater dominated period before radiation domination and show that the isocurvature perturbation is generated during the phase transition and leaves imprint in the observable signatures for small scale structure.