Thermalization in the presence of a time-dependent dissipation and its impact on dark matter production

In standard cosmological scenarios, a heavy meta-stable field dominates the energy density of the universe after inflation. The dissipation of this field continuously sources high-energy particles. In general, the dissipation rate of this meta-stable field can have a non-trivial time dependence. We study the impact of this time-dependent dissipation rate on the thermalization of the high-energy decay products of the meta-stable field. These energetic particles can contribute substantially to dark matter production in addition to the usual production from the thermal bath particles during reheating. We investigate the impact of this generalized dissipation on dark matter production in a model-independent way. We illustrate the parameter space that explains the observed dark matter relic abundance in various cosmological scenarios. We observed that dark matter having a mass larger than the maximum temperature attained by the thermal bath can be produced from the collision of the high-energy particles which are not yet thermalized.