  The out-of-equilibrium production of dark matter (DM) from standard model
(SM) species in the early universe (freeze-in mechanism) is expected in many
scenarios in which very heavy beyond the SM fields act as mediators. In this
conference, I have talked about the freeze-in of scalar, fermionic and vector
DM though the exchange of moduli fields \cite{chowdhury_moduli_2019}, which are
in the low-energy spectrum of many extra-dimensions and string theory
frameworks. We have shown that the high-temperature dependencies of the
production rate densities in this model, as well as the possibility of having
moduli masses at the post-inflationary reheating scale, make it crucial to
consider the contribution of the freeze-in prior the start of the standard
radiation era for a correct prediction of the DM relic density.
