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

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 B(V → ℓαℓβ), where V = ϕ,ψ(n), Υ(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 nonstandard sterile fermions is parametrized by means of one heavy sterile (Majorana) neutrino. [ABSTRACT FROM AUTHOR]