Gauge invariance and finite width effects in radiative two-pion tau leptondecay - art. no. 033007

The contribution of the rho(+/-) vector meson to the tau-->pi pi nu gamma d ecay is considered as a potential source for the determination of the magne tic dipole moment of this light vector meson. In order to keep the gauge in variance of the whole decay amplitude, a procedure similar to the fermion-l oop scheme for charged gauge bosons is implemented to incorporate the finit e width effects of the rho(+/-) vector meson. The absorptive pieces of the one-loop corrections to the propagators and electromagnetic vertices of the rho(+/-) mason and W+/- gauge boson have identical forms in the limit of m assless particles in the loops, suggesting this to be a universal feature o f spin-one unstable particles. Model-dependent contributions to the tau-->p i pi nu gamma decay are suppressed by fixing the two-pion invariant mass di stribution at the rho mason mass value. The resulting photon energy and ang ular distribution is relatively sensitive to the effects of the rho magneti c dipole moment.