Confronting Flavour Symmetries and extended Scalar Sectors with Lepton Flavour Violation Bounds

TL;DR

This paper examines how discrete flavour symmetries impact extended scalar sectors in lepton flavour violation, showing that symmetries can impose constraints that lead to experimental exclusions of certain models.

Contribution

It highlights the interplay between flavour symmetries and scalar sectors, demonstrating how symmetries can restrict model viability under experimental bounds.

Findings

Flavour symmetries impose additional coupling relations.

Symmetries can prevent cancellations, tightening experimental constraints.

Certain models are excluded due to symmetry-induced restrictions.

Abstract

We discuss the tension between discrete flavour symmetries and extended scalar sectors arising from lepton flavour violation experiments. The key point is that extended scalar sectors will generically lead to flavour changing neutral currents, which are strongly constrained by experiments. Due to the large parameter space in the scalar sector such models will, however, usually have no big problems with existing and future bounds (even though the models might be constrained). This changes considerably once a flavour symmetry is imposed in addition: Due to the symmetry, additional relations between the different couplings arise and cancellations become impossible in certain cases. The experimental bounds will then constrain the model severely and can easily exclude it. We consider two examples which show how these considerations are realized. The same logic should apply to a much wider class of models.