Electroweak Baryogenesis from Dark-Sector $CP$ Violation

We present a novel mechanism of electroweak baryogenesis where $CP$ violation occurs in a dark sector, comprised of standard model gauge singlets, thereby evading the strong electric dipole moment constraints. In this framework, the background of the timelike component of a new gauge boson $Z_{\mu }^{\prime }$, generated at electroweak temperatures, drives the electroweak sphaleron processes to create the required baryon asymmetry. We first discuss the crucial ingredients for this mechanism to work, and then show that all of them can be elegantly embedded in ultraviolet completions with a spontaneously broken gauged lepton number. The models under consideration have a rich phenomenology and can be experimentally probed in leptophilic $Z^{\prime }$ searches, dark matter searches, heavy Majorana neutrino searches, as well as through hunting for new Higgs portal scalars in multilepton channels at colliders.

Figure 1

We scan broadly over the model parameters to find points that allow for successful EWBG as proposed in this Letter (blue points). We show various experimental constraints (LEP, BABAR, beam dump, electron, and muon $g-2$, TEXONO, Borexino, CCFR) by the correspondingly labeled shaded regions, in the gauged $L_e+L_{\mu }+L_{\tau }$ (left) and $L_{\mu }+L_{\tau }$ (right) models.