Abstract
We calculate the production rate of singlet fermions from the decay of neutral or charged scalar fields in a hot plasma. We find that there are considerable thermal corrections when the temperature of the plasma exceeds the mass of the decaying scalar. We give analytic expressions for the temperature-corrected production rates in the regime where the decay products are relativistic. We also study the regime of non-relativistic decay products numerically. Our results can be used to determine the abundance and momentum distribution of Dark Matter particles produced in scalar decays. The inclusion of thermal corrections helps to improve predictions for the free streaming of the Dark Matter particles, which is crucial to test the compatibility of a given model with cosmic structure formation. With some modifications, our results may be generalised to the production of other Dark Matter candidates in scalar decays.
Highlights
Explanation make the DM hypothesis very compelling
The probably strongest motivation for sterile neutrinos in the strict sense, i.e. right handed neutrinos νR that do mix with νL, are the observed neutrino oscillations, which have been awarded with the 2015 Nobel Prize in physics
In the SM neutrinos only exist with left handed (LH) chirality, while all other fermions come with LH and right handed (RH) chirality
Summary
Speculations about the existence of heavy neutrinos N have been motivated for various other reasons, see [3] for a review. The free streaming of N and its effect on structure formation provide another way to constrain the parameter space These depend strongly on the N phase space distribution function fN , which is determined by the way the heavy neutrinos are produced in the early universe. This already appears to exclude the scenario where all DM is composed of thermally produced N for μα = 0 (i.e. in absence of a MSW resonance) [52, 58]. At present it seems likely that thermally produced sterile neutrinos can explain all the observed DM consistent with the formation of small scale structure only if their production is resonantly enhanced by lepton asymmetries μα. We compute thermal corrections to the abundance and momentum distribution of N -particles
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