Lepton-pair production in dipion τ lepton decays

We study the tau(-) -> nu(tau)pi(-)pi(0)l(+)l(-) (l = e, mu) decays, which are O(alpha(2)) suppressed with respect to the dominant di-pion tau decay channel. Both the inner bremsstrahlung and the structure- (and model-) dependent contributions are considered. In the l = e case, structure-dependent effects are O(1%) in the decay rate, yielding a clean prediction of its branching ratio, 2.3 x 10(-5), measurable with BABAR or Belle(-II) data. For l = mu is, both contributions have a similar magnitude, and we get a branching fraction of (1.6 +/- 0.3) x 10(-7), reachable by the end of Belle-II operation. These decays allow one to study the dynamics of strong interactions with simultaneous weak and electromagnetic probes; their knowledge will contribute to reducing backgrounds in lepton flavor and lepton number violating searches.