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

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.