Lepton flavor violating decays of vector quarkonia and of the $Z$ boson

TL;DR

This paper investigates how sterile fermions can enhance lepton flavor violating decays of quarkonia and the Z boson, providing calculations and models that demonstrate potential significant effects in certain scenarios.

Contribution

It presents detailed calculations of Wilson coefficients and explores the impact of sterile fermions on LFV decays within specific models like the inverse seesaw and effective sterile neutrino models.

Findings

LFV decay rates can be significantly enhanced with large sterile fermion masses.

Active-sterile mixing plays a crucial role in the magnitude of LFV decay enhancements.

The models demonstrate potential observable effects in future experiments.

Abstract

We address the impact of sterile fermions on the lepton flavor violating decays of quarkonia as well as of the $Z$ boson. We compute the relevant Wilson coefficients and show that the ${\rm B}(V\to\ell_\alpha\ell_\beta)$, where $V=\phi,\psi^{(n)}$, $\Upsilon^{(n)},Z$ can be significantly enhanced in the case of large sterile fermion masses and a non-negligible active-sterile mixing. We illustrate that feature in a specific minimal realization of the inverse seesaw mechanism, known as $(2,3)$-ISS, and in an effective model in which the presence of non-standard sterile fermions is parameterized by means of one heavy sterile (Majorana) neutrino.