Abstract.
I will present in this talk recent works concerning the production of
particles (thermal bath as well as dark matter), in the earliest stage of
the Universe, between the preheating phase and the reheating time. I will
insist on the subtleties of backreactions from scattering of the inflaton
and apply it to the mechanism to the dark matter production in minimal
extensions of the Standard Model, especially gravitational production.
(The slides will be available here)