Less Minimal Flavour Violation

TL;DR

This paper analyzes the approximate U(2)^3 flavour symmetry in the quark sector of the Standard Model, deriving bounds on symmetry-breaking parameters and exploring implications for CP violation and Minimal Flavour Violation.

Contribution

It provides a comprehensive effective field theory analysis of flavour symmetry breaking parameters and their experimental bounds, including recent CP violation observations.

Findings

Significant bounds on flavour-breaking parameters from epsilon'/epsilon.

Potential explanation for CP violation in D decays within the framework.

Constraints consistent with Minimal Flavour Violation scenarios.

Abstract

We consider the approximate U(2)^3 flavour symmetry exhibited by the quark sector of the Standard Model and all its possible breaking terms appearing in the quark Yukawa couplings. Taking an Effective Field Theory point of view, we determine the current bounds on these parameters, assumed to control the breaking of flavour in a generic extension of the Standard Model at a reference scale Lambda. In particular, a significant bound from epsilon'/epsilon is derived, which is relevant to Minimal Flavour Violation as well. In the up-quark sector, the recently observed CP violation in D -> pi+ pi-, K+ K- decays might be accounted for in this generic framework, consistently with any other constraint.