Vector mesons in nuclear μ^--e^- conversion

We study nuclear µ−–e− conversion in the general framework of an effective Lagrangian approach without referring to
any specific realization of the physics beyond the Standard Model (SM) responsible for lepton flavor violation (L/f ). We show
that vector meson exchange between lepton and nucleon currents plays an important role in this process. A new issue of this
mechanism is the presence of the strange quark vector current contribution induced by the φ meson. This allows us to extract
new limits on the L/f lepton–quark effective couplings from the existing experimental data.