Thermal Fluctuations of Dark Matter in Bouncing Cosmology

TL;DR

This paper studies the behavior of dark matter thermal fluctuations in bouncing cosmology, deriving their evolution and stability, and suggests these fluctuations could help distinguish bouncing cosmology from inflation.

Contribution

It provides a detailed analysis of super-horizon thermal perturbations of dark matter in bouncing cosmology, highlighting their stability and potential observational significance.

Findings

Super-horizon dark matter fluctuations are stable in bouncing cosmology.

These fluctuations differ from inflationary predictions, offering a way to test bouncing models.

The evolution of thermal perturbations does not disrupt the bouncing universe background.

Abstract

We investigate the statistical nature of the dark matter particles produced in bouncing cosmology, especially, the evolution of its thermal fluctuations. By explicitly deriving and solving the equation of motion of super-horizon mode, we fully determine the evolution of thermal perturbation of dark matter in a generic bouncing background. And we also show that the evolution of super-horizon modes is stable and will not ruin the background evolution of a generic bouncing universe till the Planck scale. Given no super-horizon thermal perturbation of dark matter appears in standard inflation scenario such as WIMP(-less) miracles, such super-horizon thermal perturbation of dark matter generated during the generic bouncing universe scenario may be significant for testing and distinguishing these two scenario in near future.