A Real CKM Matrix and Physics Beyond the Standard Model

TL;DR

This paper explores the possibility of a real CKM matrix with CP violation arising from new physics beyond the Standard Model, analyzing experimental constraints and specific model implications.

Contribution

It demonstrates that a real CKM matrix is compatible with current data if new physics affects B_d mixing and CP violation, and examines multi-Higgs models for naturalness.

Findings

A real CKM matrix can fit current experimental data with additional new physics contributions.

A specific two-Higgs-doublet model can generate CP asymmetries consistent with observations.

New physics must contribute significantly to B_d mixing to allow a real CKM matrix.

Abstract

We study the possible existence of a real Cabibbo-Kobayashi-Maskawa (CKM) matrix, with CP violation originating from physics beyond the standard model (SM). We show that present experimental data allow for a real CKM matrix provided that new physics also contributes to Delta m_{B_d} by at least 20% of the SM contribution (for rho > 0), besides generating CP violation in the kaon sector. The naturalness of a real CKM matrix is studied within the framework of general multi-Higgs-doublet models with spontaneous CP violation. As an example, we discuss a specific two-Higgs-doublet model and its implications for CP asymmetries in non-leptonic neutral B-meson decays.