Baryogenesis and dark matter freeze-in from Higgs interactions
We present a model of freeze-in dark matter (DM) and baryogenesis in which the new particles are a TeV-scale electroweak-doublet vector-like fermion (VLF) and two gauge-singlet Majorana fermions that constitute the DM, the heavier one with a mass in the tens-to-hundreds of keV range. Feeble Yukawa couplings of the VLF to the DM and the Standard Model Higgs doublet induce freeze-in production of the DM via VLF decays in the early universe. Due to a CP-violating phase in these couplings, DM propagation and rescattering induce opposite charge asymmetries in the VLF and SM sectors. Even in the absence of $B-L$ violation, the VLF asymmetry guarantees a baryon asymmetry once in-equilibrium SM interactions are taken into account. A relatively small conversion factor from VLF asymmetry to baryon asymmetry is balanced by a more direct asymmetry generation mechanism than in other minimal models of freeze-in baryogenesis. The observed DM energy density requires the heavier DM particle to remain well out of equilibrium throughout production. This allows us to map out the VLF mass-lifetime space using a novel perturbative calculation of the baryon asymmetry. We find that the model is already significantly constrained by LHC searches and structure formation probes, which will continue to test interesting parameter space in the coming years. The addition of VLF Yukawa couplings not involving the DM breaks $B-L$ and greatly expands the viable parameter space, while inducing potential signatures from dark matter decay and lepton flavor violation.