New avenues for tau flavor violation

TL;DR

The paper addresses how tau flavor violation can reveal the underlying breaking of lepton flavor symmetries in nature. It uses the SMEFT framework to organize CLFV by the amount of flavor violation (one-, two-, or three-unit shifts) and surveys the corresponding processes, experimental strategies, and current constraints, highlighting the tau sector's unique sensitivity. A key contribution is detailing how two-unit LFV can be probed at $d=6$ with channels beyond the conventional $\ell\to\ell'\gamma$ searches, including universality tests that constrain related operators, as well as the necessity of light mediators to render three-unit LFV observable. The work emphasizes broad, bias-free exploration of model space to map viable new-physics scenarios and guide experimental efforts at facilities like Belle II and future $Z$-factories.

Abstract

I present a concise overview of tau flavor violation and the broad opportunities it offers, with a focus on non-standard decay channels and their underlying theoretical motivations.

Figures (1)

• Figure 1: CLFV processes (only one representative shown per group) organized by their $U(1)_{L_\mu-L_\tau}\times U(1)_{L_\mu+ L_\tau -2 L_e}$ breaking, adapted from Ref. Heeck:2016xwg.