Effective-field theory analysis of the $\tau^- \to \eta^{(\prime)} \pi^- \nu_\tau$ decays

TL;DR

This paper investigates the rare tau decays into eta or eta prime and a pion, using effective field theory to explore potential new physics effects beyond the Standard Model, especially scalar interactions.

Contribution

It provides a comprehensive EFT analysis of tau decays, highlighting their sensitivity to scalar interactions and potential to set stronger constraints than existing low-energy measurements.

Findings

Observables in these decays can constrain scalar interactions more effectively.

SM isospin breaking amplitudes are strongly suppressed, enhancing sensitivity.

The analysis assumes massless neutrinos and includes general dimension-six interactions.

Abstract

The rare $\tau^- \to \eta^{(\prime)} \pi^- \nu_\tau$ decays, which are suppressed by $G$-parity in the Standard Model (SM), can be sensitive to the effects of new interactions. We study the sensitivity of different observables of these decays in the framework of an effective field theory that includes the most general interactions between SM fields up to dimension six, assuming massless neutrinos. Owing to the strong suppression of the SM isospin breaking amplitudes, we find that the different observables would allow to set constraints on scalar interactions that are stronger than those coming from other low-energy observables.