Abstract
It has been proposed that in a part of the parameter space of the Standard Model completed by three generations of keV…GeV right-handed neutrinos, neutrino masses, dark matter, and baryon asymmetry can be accounted for simultaneously. Here we numerically solve the evolution equations describing the cosmology of this scenario in a 1+2 flavour situation at temperatures T ≤ 5 GeV, taking as initial conditions maximal lepton asymmetries produced dynamically at higher temperatures, and accounting for late entropy and lepton asymmetry production as the heavy flavours fall out of equilibrium and decay. For 7 keV dark matter mass and other parameters tuned favourably, ∼ 10% of the observed abundance can be generated. Possibilities for increasing the abundance are enumerated.
Highlights
GeV-scale right-handed neutrinos freeze out and decay
We numerically solve the evolution equations describing the cosmology of this scenario in a 1+2 flavour situation at temperatures T ≤ 5 GeV, taking as initial conditions maximal lepton asymmetries produced dynamically at higher temperatures, and accounting for late entropy and lepton asymmetry production as the heavy flavours fall out of equilibrium and decay
These non-equilibrium decays release entropy [20], an effect which has been argued to be substantial for MH 1 . . . 10 GeV [21], and which needs to be included in dark matter and baryogenesis computations. (When πT MH, the GeV-scale flavours already have a small effect on the energy and entropy densities, this is on the percent level and insignificant on our resolution.)
Summary
The GeV-scale flavours that are responsible for leptogenesis at T ∼ 130 GeV, freeze out and subsequently decay when πT MH These non-equilibrium decays release entropy [20], an effect which has been argued to be substantial for MH 1 . (When πT MH, the GeV-scale flavours already have a small effect on the energy and entropy densities, this is on the percent level and insignificant on our resolution.). D3 kt (2π) the corresponding phase space integral, the energy density and pressure carried by the heavy flavours can be expressed as eH =. It is helpful to express the phase-space integrals in eq (3.5) in terms of the time-independent variable k (cf eq (3.4)), because ρ+II appears in a form for which a time-evolution equation is available. Defining Y ≡ n/sT , evolution equations for particle densities and phase space distributions from section 2 are transcribed as
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