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 Ωch2=0.1193±0.0014, 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.
Highlights
Assuming Newtonian gravity, and its extension into General Relativity, describes gravitational forces correctly, astronomical and cosmological observations show that most of the matter in our Universe is a non-luminous, neutral form of matter, called dark matter (DM)
There are several reasons for the popularity of weakly interactive massive particles (WIMPs). If they once were in full chemical equilibrium with the particles of the Standard Model (SM), which is true if the largest temperature after the most recent period of entropy production exceeded about 5% of the WIMP mass, the WIMP relic density can be calculated unambiguously for a given cosmological model, independent of initial conditions, using only particle physics quantities as input
Using recent lattice QCD results with dynamical quarks for the equation of state, we have computed the energy and entropy densities of the SM with emphasis on temperatures around the deconfinement transition at Tc = 154 MeV
Summary
Assuming Newtonian gravity, and its extension into General Relativity, describes gravitational forces correctly, astronomical and cosmological observations show that most of the matter in our Universe is a non-luminous, neutral form of matter, called dark matter (DM). There are several reasons for the popularity of WIMPs. There are several reasons for the popularity of WIMPs If they once were in full chemical equilibrium with the particles of the Standard Model (SM), which is true if the largest temperature after the most recent period of entropy production exceeded about 5% of the WIMP mass, the WIMP relic density can be calculated unambiguously for a given cosmological model, independent of initial conditions, using only particle physics quantities (masses and couplings, or cross sections) as input. This calculation yields approximately the observed relic density for roughly weak–strength WIMP annihilation cross sections.
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