Constraints on leptoquarks from lepton-flavour-violating tau-lepton processes

TL;DR

This paper investigates how leptoquarks can induce lepton-flavour violation in tau processes, deriving bounds on their couplings by translating effective field theory constraints into leptoquark parameters.

Contribution

It provides a model-independent analysis of leptoquark couplings to tau leptons by translating effective operator bounds into specific leptoquark interaction limits.

Findings

Derived bounds on leptoquark couplings from tau decay data.

Connected effective field theory constraints to leptoquark models.

Analyzed both scalar and vector leptoquarks in lepton-flavour violation contexts.

Abstract

Leptoquarks are ubiquitous in several extensions of the Standard Model and seem to be able to accommodate the universality-violation-driven $B$-meson-decay anomalies and the $(g-2)_\mu$ discrepancy interpreted as deviations from the Standard Model predictions. In addition, the search for lepton-flavour violation in the charged sector is, at present, a major research program that could also be facilitated by the dynamics generated by leptoquarks. In this article, we consider a rather wide framework of both scalar and vector leptoquarks as the generators of lepton-flavour violation in processes involving the tau lepton. We single out its couplings to leptoquarks, thus breaking universality in the lepton sector, and we integrate out leptoquarks at tree level, generating the corresponding dimension-6 operators of the Standard Model Effective Field Theory. In Ref. [1] we obtained model-independent bounds on the Wilson coefficients of those operators contributing to lepton-flavour-violating hadron tau decays and $\ell$-$\tau$ conversion in nuclei, with $\ell=e,\mu$. Hence, we use those results to translate the bounds into the couplings of leptoquarks to the Standard Model fermions.