Gravitational production of nearly thermal fermionic Dark Matter

Understand

We consider the cosmological production of fermionic dark matter during inflation and a post-inflationary radiation dominated era.

• This fermion \emph{only interacts gravitationally}, has a mass $m$ much smaller than the Hubble scale during inflation (but is otherwise arbitrary) and is in its Bunch-Davies vacuum state during inflation.
• We focus on superhorizon modes at the end of inflation, and assume instantaneous reheating.
• We obtain the full energy momentum tensor discussing its renormalization, and show that the contribution from particle production is of the kinetic-fluid form near matter-radiation equality.