CP Violation in the scalar sector

TL;DR

This paper explores how extended scalar sectors, especially multi-Higgs models, can introduce new sources of CP violation affecting gauge boson couplings and discusses constraints and possibilities for spontaneous CP violation.

Contribution

It analyzes CP violation mechanisms in two- and three-Higgs-doublet models, highlighting the impact on gauge couplings and the role of symmetries in spontaneous CP violation.

Findings

CP violation can arise in trilinear gauge couplings in two-Higgs-doublet models.

Alignment limit constrains CP-violating couplings.

Multiple complex vacua in three-Higgs-doublet models with $S_3$ symmetry can lead to spontaneous CP violation.

Abstract

Models with an extended scalar sector may in principle provide new sources of CP violation originating in the scalar potential. One of the simplest ways to implement this idea is to have CP violation in a two-Higgs-doublet model. Here, it leads to CP violation in trilinear weak gauge boson couplings. We discuss how these couplings are becoming constrained in the alignment limit. In a model with three Higgs doublets, subject to an $S_3$ symmetry, several complex vacua are possible. Some of these, but not all, may lead to spontaneous CP violation.