Lepton-flavour-violating tau decays from triality

TL;DR

This paper explores models with lepton flavour triality predicting tau decays violating lepton flavor, which could be observed soon at Belle II, involving doubly-charged scalar mediators.

Contribution

It introduces new theories based on lepton flavour triality with specific decay signatures and analyzes their phenomenology with doubly-charged scalars as mediators.

Findings

Predicted tau decay modes are within reach of upcoming experiments.

Doubly-charged scalars are key mediators in these flavor-violating processes.

Models provide testable signatures for physics beyond the standard model.

Abstract

Motivated by flavour symmetry models, we construct theories based on a low-energy limit featuring lepton flavour triality that have the flavour-violating decays $\tau^\pm \to \mu^\pm \mu^\pm e^\mp$ and $\tau^\pm \to e^\pm e^\pm \mu^\mp$ as the main phenomenological signatures of physics beyond the standard model. These decay modes are expected to be probed in the near future with increased sensitivity by the Belle II experiment at the SuperKEKB collider. The simple standard model extensions featured have doubly-charged scalars as the mediators of the above decay processes. The phenomenology of these extensions is studied here in detail.