Dark matter production during the thermalization era

Keisuke Harigaya,Kyohei Mukaida,Masaki Yamada

doi:10.1007/jhep07(2019)059

Keisuke Harigaya, Kyohei Mukaida + Show 1 more

Open Access

https://doi.org/10.1007/jhep07(2019)059

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Abstract

We revisit the non-thermal dark matter (DM) production during the thermalization and reheating era after inflation. The decay of inflaton produces high-energy particles that are thermalized to complete the reheating of the Universe. Before the thermalization is completed, DM can be produced from a collision between the high-energy particles and/or the ambient plasma. We calculate the DM abundance produced from these processes for the case where the cross section of the DM production is proportional to the n-th power of the center of mass energy. We find that the collision between the high-energy particles is almost always dominant for n ≳ 4 while it is subdominant for n≲2. The production from the ambient plasma is dominant when n≲3 and the reheating temperature is of the order of or larger than the DM mass. The production from a collision between the high-energy particle and the ambient plasma is important for n ≲ 2 and the reheating temperature is much lower than the DM mass.

Highlights

We calculate the dark matter (DM) abundance produced from these processes for the case where the cross section of the DM production is proportional to the n-th power of the center of mass energy
We will see that the contribution (A) is dominant when the cross section of DM production depends positively and strongly on the center of mass energy as considered in ref
The contribution (B) is important when the cross section is mildly dependent on the center of mass energy and the reheating temperature is much lower than the DM mass

Summary

Thermalization era

We briefly review the thermalization process of inflaton decay products, which is relevant to the computation of the non-thermal production rate of dark matter in the post-reheating era. Where Γφ is the decay rate of the inflaton After this happens t tmax, the energy and number density of radiation is dominated by the thermalized sector. High-energy particles are continuously produced from the inflaton decay until the Hubble parameter decreases to the decay rate: Γφ H This is the time when the reheating is completed and the Universe becomes to be dominated by thermal radiation. This process is completed within a Hubble time for T < Tmax, there remains a tail of cascading particles because the inflaton continuously sources the high-energy particles. The spectrum of these cascading particles can be estimated as follows. The scattering involving particles in the high-energy tail is the dominant process when the cross section of DM production process positively depends on the center of mass energy and/or the reheating temperature is smaller than the DM mass

DM production during the thermalization era

Conclusions and discussion