FIMP Dark Matter from Leptogenesis in Fast Expanding Universe

Within the framework of canonical type-I seesaw, a feebly interacting massive particle (FIMP) $\chi$ is introduced as dark matter candidate. The leptogenesis mechanism and relic density share common origin via decays Majorana neutrinos $N$. Provided an additional species $\varphi$ whose energy red-shifts $\rho_{\varphi}\propto a^{-(4+n)}$, Hubble expansion rate larger than standard scenario, i.e., Universe expands faster. consequences such fast expanding on well FIMP are investigated in detail. We demonstrate significant impact final baryon asymmetry abundance due to existence for strong washout scenario. While weak effects FEU relatively small. introduce scale factors $F_L$ $F_\chi$ describe corresponding FEU. A semi-analytical approach derive efficiency $\eta_L$ $\eta_\chi$ also discussed. viable parameter space success thermal correct DM obtained cosmology Our results show that it possible distinguish different scenarios cases.