Baryogenesis from spontaneous CP violation in the early Universe

TL;DR

This paper introduces a new electroweak-scale baryogenesis mechanism involving spontaneous CP violation driven by a CP-odd scalar, which occurs early in the Universe and avoids current experimental constraints, with testable predictions.

Contribution

It presents a novel baryogenesis scenario using a non-minimal Higgs sector with spontaneous CP violation that is testable through collider and flavor experiments.

Findings

Identifies parameter space for early Universe CP violation in 2HDM + $a$ model.

Shows the scenario is consistent with current experimental constraints.

Predicts signatures accessible to LHC and flavor physics experiments.

Abstract

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 non-minimal Higgs sector consisting of two Higgs doublets and a singlet pseudoscalar (2HDM + $a$). We analyze the region of the 2HDM + $a$ 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 flavour measurements.