G -parity breaking in τ−→η(′)π−ντ decays induced by the η(′)γγ form factor
Physical Review D
Breaking of G-parity or new weak (second class) currents can be responsible for τ^- →η^(')π^- ν_τ decays. Forthcoming measurements of τ lepton properties at the Belle II experiment will be able to measure this decay channel for the first time. Isolating new physics contributions from the measured rates will require a careful evaluation of G-parity breaking contributions. Here we evaluate the one-loop contribution to τ^- →η^(')π^- ν_τ decays induced by the emission of two virtual photons and its
... later conversion into an η^(') meson. As expected, this contribution is very small and may be relevant only for new physics searches contributing at the 10^-4 level to the decay rate of τ^- →η^(')π^- ν_τ .