$E_6$ Unification of Freeze-In Dark Matter and Leptogenesis

Abstract: We investigate the possibility of \emph{freeze-in} dark matter production and baryogenesis in an $E_6$ extension of the Standard Model, featuring a residual $U(1){\psi'}$ gauge symmetry. This symmetry arises from a linear combination of $U(1)\chi$ and $U(1){\psi}$, both of which are subgroups of the $E_6$. The spontaneous breaking of $U(1)_{\psi'}$ symmetry governs the dynamics of a singlet fermion, which naturally serves as a freeze-in dark matter candidate. The dark matter mass arises from dimension-five operators, and a discrete symmetry ensures their stability. We show that freeze-in production from scalar decay can yield the correct relic abundance for dark matter masses between few MeV to a few hundred GeV. Simultaneously, heavy right-handed neutrinos generate light neutrino masses via the type-I seesaw and produce the observed baryon asymmetry via leptogenesis.