On UV sensitivities of non-renormalizable operators for freeze-in production of dark matter in modified cosmologies

The aim of this thesis is to investigate particle production in the early universe via scattering processes mediated by non-renormalizable operators. Famously , such a production is dominated at the very high temperatures where the universe became radiation dominated after cosmic inflation. However, if one considers modified cosmological histories this is not true anymore. This thesis will investigate motivated cosmological scenarios with a different expansion history and it will assess how particle production is affected