LCSR application to radiative tau decay

The non-perturbative QCD e ects involved in radiative tau decay (iota(-) -> pi(-) nu(iota)gamma agW) are encoded in two form factors (FFs); vector (F-V) and axial-vector (F-A). These FFs are the same as those involved in radiative pion decay with the crucial di erence that the square of the momentum transferred, t, between the pi - gamma system is positive. This makes them timelike and can result in the production of real hadronic resonances. We calculate the analytical form for these FFs using the method of light-cone sum rules (LCSR) and present the decay width and the invariant mass spectrum of the pi - gamma system. The structure-dependent parameter gamma (i.e., F-A/F-V at zero momentum transfer) is found to be in good agreement with the experimental determination.