Bounds on lepton flavor violating physics and decays of neutral mesons from τ (μ) →3â.,", â.,"γγ -decays

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neu-
tral vector bosons V = ρ0, ω, φ, J/ψ, Υ, Z0, as well as pseudoscalar P = π0, η, η′, ηc and scalar
S = f0(500), f0(980), a0(980), χc0(1P ) mesons, without referring to a specific mechanism of LFV
realization. In particular, we relate the rates of the three-body LFV decays τ (μ) → 3`, where ` = μ
or e, to the two-body LFV decays (V, P ) → τ μ(τ e, μe), where V and P play the role of intermediate
resonances in the decay process τ (μ) → 3`. From the experimental upper bounds for the branching
ratios of τ (μ) → 3` decays, we derive upper limits for the branching ratios of (V, P ) → τ μ(τ e, μe).
We compare our results to the available experimental data and known theoretical upper limits from
previous studies of LFV processes and find that some of our limits are several orders of magnitude
more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton
dimension-six LFV operators from data on lepton decays. Some of these limits are either new or
stronger than those existing in the literature.