The Effects of QCD Equation of State on the Relic Density of WIMP Dark Matter

TL;DR

This paper refines the calculation of WIMP dark matter relic density by incorporating recent lattice QCD results, significantly improving theoretical precision to match observational data, especially for WIMP masses between 3 and 15 GeV.

Contribution

It introduces updated relic density predictions using lattice QCD, reducing theoretical uncertainties and highlighting differences from previous models for specific WIMP mass ranges.

Findings

Relic density predictions differ by up to 9-12% for certain WIMP masses.

Updated calculations improve alignment with Planck observational data.

QCD effects are most significant for WIMP masses between 3 and 15 GeV.

Abstract

Weakly Interactive Massive Particles (WIMPs) are the most widely studied candidate particles forming the cold dark matter (CDM) whose existence can be inferred from a wealth of astrophysical and cosmological observations. In the framework of the minimal cosmological model detailed measurements on the cosmic microwave background by the PLANCK collaboration fix the scaled CDM relic density to $\Omega_{c}h^2=0.1193\pm0.0014$, with an error of less than 1.5%. In order to fully exploit this observational precision, theoretical calculations should have a comparable or smaller error. In this paper we use recent lattice QCD calculations to improve the description of the thermal plasma. This affects the predicted relic density of "thermal WIMPs", which once were in chemical equilibrium with Standard Model particles. For WIMP masses between 3 and 15 GeV, where QCD effects are most important, our predictions differ from earlier results by up to 9% (12%) for pure S-wave (P-wave) annihilation. We use these results to compute the thermally averaged WIMP annihilation cross section that reproduces the correct CDM relic density, for WIMP masses between 0.1 GeV and 10 TeV.