Semileptonic τ decays: powerful probes of non-standard charged current weak interactions

Pablo Roig

doi:10.1051/epjconf/201921208002

Abstract

When looking for heavy (O(few TeV)) New Physics, the most eﬃcient way to bene?t from both high and low-energy measurements simultaneously is the use of the Standard Model Eﬀective Field Theory (SMEFT). In this talk I highlight the importance of semileptonic τ decays in complementing, in this respect, the traditional low-energy precision observables and high-energy measurements. This is yet another reason for considering hadronic tau decays as golden channels at Belle-II beyond the unquestionable interest of the CP violation anomaly in τ → KS πντ decays, that I also discuss within the eﬀective theory. A couple of new results for τ−→ K− ντ decays are also included.

Highlights

IntroductionImagine four fermion weak interactions are modified, with respect to the Standard Model (SM) 1, by the exchange of new heavy mediators with O(10) TeV masses
Effective field theory applicationI explain the first sentence of the abstract above
When looking for heavy (O(few TeV)) New Physics, the most efficient way to benefit from both high and low-energy measurements simultaneously is the use of the Standard Model Effective Field Theory (SMEFT)

Summary

Introduction

Imagine four fermion weak interactions are modified, with respect to the Standard Model (SM) 1, by the exchange of new heavy mediators with O(10) TeV masses At this energy scale one must include all renormalizable operators of dimension 4 consistent with the underlying local gauge symmetry in the Lagrangian, including both SM and beyond the SM (BSM) degrees of freedom. Instead, we look at the same processes at E ∼ 1 TeV, the heavy BSM degrees of freedom are no longer dynamical and they should be integrated out from the action This will give rise (in addition to the SM Lagrangian) to an infinite tower of (classically) non-renormalizable operators written in terms of the SM fields. The main results of applying eq (1) to hadronic tau decays in searching for heavy NP in a model-independent way will be discussed, and compared to other low- and high-energy probes in the remainder of this contribution

Application to semileptonic tau decays

Conclusions