Post-Reheating Inflaton-Mediated Dark and Visible Matter Scatterings: A Cosmological Perspective

The initial density of both the Dark Matter(DM) and the Standard Model (SM) particles may be produced via perturbative decay of inflaton with different decay rates, creating an initial temperature ratio, $\xi=T_{DM,i}/T_{SM,i}$. This scenario implies inflaton mediated scatterings between the DM and the SM, that can modify the temperature ratio. The effect of these scatterings is studied in a gauge-invariant model of inflaton interactions upto dimension-5 with all the SM particles including Higgs. It is observed that a lower (or higher) initial dark matter (DM) temperature will rapidly rise (or fall), even with minimal couplings to the inflaton. There is a stringent lower limit on the DM mass to satisfy the relic density, as faster back-scattering processes deplete DM into SM particles. Both the BBN and CMB constraints become stronger for $\xi_i<1$, probing values as small as $10^{-4}$. In particular, CMB constraints become important to probe light dark matter scenario, with smaller $\xi_i$ values.