Towards precise baryogenesis in the 2HDM$+a$

TL;DR

This paper investigates baryogenesis within a non-minimal Higgs sector model, highlighting a transient CP violation mechanism that aligns with experimental constraints and offers testable predictions for future collider and flavor experiments.

Contribution

It provides a detailed, improved computation of baryon asymmetry in the 2HDM+a model, demonstrating a predictive scenario compatible with current constraints and accessible to near-future tests.

Findings

Baryon asymmetry is suppressed compared to previous estimates.

Larger mixing between singlet and pseudoscalars is required for successful baryogenesis.

Model predictions are testable with upcoming collider and flavor experiments.

Abstract

We perform a detailed investigation of the viable baryogenesis parameter space of a non-minimal Higgs sector consisting of two Higgs doublets and a singlet pseudoscalar (2HDM$+a$). In such a model, an early Universe period of transient CP violation may occur, driven by a nonvanishing vacuum expectation value of the CP-odd scalar $a$. This naturally avoids the stringent electric dipole moment experimental constraints on beyond-the-Standard-Model sources of CP violation. We provide a state-of-art computation of the baryon asymmetry, providing several important improvements over existing baryogenesis computations for this model. We show that the required thermal history and successful baryogenesis lead to a predictive scenario, testable in the near future by a combination of LHC searches and low-energy flavour measurements. Our improved predictions for the baryon asymmetry find that it is rather suppressed compared to earlier predictions, requiring larger mixing between the singlet and 2HDM pseudoscalars and hence leading to a more easily testable model at colliders.