A soft origin for CKM-type CP violation

TL;DR

This paper introduces a two-Higgs-doublet model with a Z3 symmetry where CP violation arises solely from a soft scalar potential term, affecting only the CKM matrix and suppressing flavor-changing neutral currents.

Contribution

The model demonstrates a novel mechanism where CP violation is confined to the CKM matrix through a soft scalar coupling, with minimal parameters and suppressed flavor-changing neutral interactions.

Findings

CP violation originates solely in the CKM matrix.

Neutral scalar Yukawa interactions are all real in the mass basis.

Scalar masses can be as low as a few hundred GeV due to suppressed flavor-changing neutral currents.

Abstract

We present a two-Higgs-doublet model, with a $\mathbbm{Z}_3$ symmetry, in which CP violation originates solely in a soft (dimension-2) coupling in the scalar potential, and reveals itself solely in the CKM (quark mixing) matrix. In particular, in the mass basis the Yukawa interactions of the neutral scalars are all real. The model has only eleven parameters to fit the six quark masses and the four independent CKM-matrix observables. We find regions of parameter space in which the flavour-changing neutral couplings are so suppressed that they allow the scalars to be no heavier than a few hundred GeV.