Abstract
We show how knowledge of the cold dark matter (CDM) density can be used, in conjunction with measurements of the parameters of a scenario for beyond the Standard Model (BSM) physics, to provide information about the evolution of the Universe before Big Bang Nucleosynthesis (BBN). As examples of non-standard evolution, we consider models with a scalar field that may decay into BSM particles, and quintessence models. We illustrate our calculations using various supersymmetric models as representatives of classes of BSM scenarios in which the CDM density is either larger or smaller than the observed density when the early Universe is assumed to be radiation-dominated. In the case of a decaying scalar field, we show how the CDM density can constrain the initial scalar density and the reheating temperature after it decays in BSM scenarios that would yield overdense dark matter in standard radiation-dominated cosmology, and how the decays of the scalar field into BSM particles can be constrained in scenarios that would otherwise yield underdense CDM. We also show how the early evolution of the quintessence field can be constrained in BSM scenarios.
Highlights
The very early Universe at temperatures ∼ 10 − 100 GeV, orders of magnitude above the scale of Big Bang Nucleosynthesis (BBN)
We show how knowledge of the cold dark matter (CDM) density can be used, in conjunction with measurements of the parameters of a scenario for beyond the Standard Model (BSM) physics, to provide information about the evolution of the Universe before Big Bang Nucleosynthesis (BBN)
In the case of a decaying scalar field, we show how the CDM density can constrain the initial scalar density and the reheating temperature after it decays in BSM scenarios that would yield overdense dark matter in standard radiation-dominated cosmology, and how the decays of the scalar field into BSM particles can be constrained in scenarios that would otherwise yield underdense CDM
Summary
The relic density calculation is generally performed in the standard cosmological model, in which the expansion rate of the Universe is given by the Friedmann equation. The radiation density reads ρrad(T. where geff is the effective number of degrees of freedom of radiation, which is given by the particle content of the Standard Model and the QCD equation of state (see, for example, [41, 42]). With heff the effective number of entropic degrees of freedom of radiation To solve this set of equations, one defines the ratio of the number density of BSM particles to the radiation entropy density Y (T ) ≡ n(T )/srad(T ), and the ratio of the relic particle mass to the temperature, x ≡ mrelic/T , and combines them into [43, 44]: dY =−. Since it was shown that the theoretical uncertainties due to the cross section calculation at tree level and to the uncertainties in the QCD equation of state are of the order of a tenth [36, 37, 41, 42, 48, 49], we add a 10% theoretical error to the Planck measurements and obtain the following 95% C.L. interval: 0.095 < Ωh2 < 0.1428
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