Lepton flavor-violating transitions in effective field theory and gluonic operators

TL;DR

This paper explores how effective field theory, especially gluonic operators, can be used to probe lepton flavor violation at multi-TeV scales through low-energy experiments and constrains new physics models like leptoquarks.

Contribution

It emphasizes the role of gluonic operators derived from heavy quark integration in lepton flavor violation and provides constraints on their Wilson coefficients from experimental data.

Findings

Constraints on gluonic operator couplings from muon conversion experiments.

Limits on lepton flavor-violating tau decays involving hadrons.

Application of results to constrain leptoquark model parameters.

Abstract

Lepton flavor-violating processes offer interesting possibilities to probe new physics at multi-TeV scale. We discuss those in the framework of effective field theory, emphasizing the role of gluonic operators. Those operators are obtained by integrating out heavy quarks that are kinematically inaccessible at the scale where low-energy experiments take place and make those experiments sensitive to the couplings of lepton flavor changing neutral currents to heavy quarks. We discuss constraints on the Wilson coefficients of those operators from the muon conversion $\mu^- + (A,Z) \to e^- + (A,Z)$ and from lepton flavor-violating tau decays with one or two hadrons in the final state, e.g. $\tau \to \ell \ \eta^{(\prime)}$ and $\tau \to \ell \ \pi^+\pi^-$ with $\ell = \mu, e$. To illustrate the results we discuss explicit examples of constraining parameters of leptoquark models.