Thermodynamics of the early Universe with mirror dark matter

TL;DR

This paper investigates how mirror dark matter influences the thermodynamics of the early Universe, especially around nucleosynthesis, revealing potential explanations for discrepancies in effective neutrino species counts.

Contribution

It provides a numerical analysis of thermodynamic evolution with a mirror sector, highlighting its impact on effective neutrino numbers during key early Universe epochs.

Findings

Effective neutrino number increases at lower temperatures.

Mirror sector affects primordial nucleosynthesis predictions.

Potential resolution of neutrino count discrepancies between epochs.

Abstract

Mirror matter is a promising self-collisional dark matter candidate. Here we study the evolution of thermodynamical quantities in the early Universe for temperatures below ~100 MeV in presence of a hidden mirror sector with unbroken parity symmetry and with gravitational interactions only. This range of temperatures is interesting for primordial nucleosynthesis analyses, therefore we focus on the temporal evolution of number of degrees of freedom in both sectors. Numerically solving the equations, we obtain the interesting prediction that the effective number of extra-neutrino families raises for decreasing temperatures before and after Big Bang nucleosynthesis; this could help solving the discrepancy in this number computed at nucleosynthesis and cosmic microwave background formation epochs.