Hadronic tau decays as New Physics probes in the LHC era

TL;DR

This paper investigates how hadronic tau decays can serve as sensitive probes for new physics beyond the Standard Model, providing precise bounds on non-standard interactions using a model-independent effective field theory approach.

Contribution

It demonstrates the potential of specific tau decay channels, especially tau to pi pi nu, to disentangle and constrain all effective couplings related to new physics in a theoretically clean manner.

Findings

Sub-percent bounds on non-standard coupling ratios to Fermi constant.

Tau decay bounds complement electroweak precision and LHC measurements.

Combined data tighten constraints on lepton universality violation.

Abstract

We analyze the sensitivity of hadronic tau decays to non-standard interactions within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Both exclusive and inclusive decays are studied, using the latest lattice data and QCD dispersion relations. We show that there are enough theoretically clean channels to disentangle all the effective couplings contributing to these decays, with the $\tau \to \pi\pi\nu_\tau$ channel representing an unexpected powerful New Physics probe. We find that the ratios of non-standard couplings to the Fermi constant are bound at the sub-percent level. These bounds are complementary to the ones from electroweak precision observables and $p p \to \tau \nu_\tau$ measurements at the LHC. The combination of tau decay and LHC data puts tighter constraints on lepton universality violation in the gauge boson-lepton vertex corrections.