We propose a variant of electroweak-scale baryogenesis characterized by the spontaneous breaking of the charge-parity ($CP$) symmetry in the early Universe driven by the vacuum expectation value of a $CP$-odd scalar. This $CP$ breaking period in the early Universe would be ended by the electroweak phase transition, with $CP$ being (approximately) conserved at present, thus avoiding the stringent electric dipole moment experimental constraints on beyond-the-Standard-Model sources of $CP$ violation. We study an explicit realization via a nonminimal Higgs sector consisting of two Higgs doublets and a singlet pseudoscalar ($2\mathrm{HDM}+a$). We analyze the region of the $2\mathrm{HDM}+a$ parameter space where such an early Universe period of $CP$ violation occurs, and show that the required thermal history and successful baryogenesis lead to a predictive scenario, testable by a combination of LHC searches and low-energy flavor measurements.

• Received 4 November 2022
• Accepted 29 March 2023

DOI:https://doi.org/10.1103/PhysRevD.107.075042

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society