Polarization effects in radiative decay of polarized $\tau$ lepton
  The polarization effects in the one-meson radiative decay of the polarized $\tau$ lepton, $\tau^-\to\pi^-\gamma\nu_{\tau}$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $\tau$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $\tau$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $\tau$ lepton polarization 3-vector in the rest frame. The vector and axial-vector form factors describing the structure-dependent part of the decay amplitude are determined using the chiral effective theory with resonances (R$\chi$T). 
G.I. Gakh, M.I. Konchatnij, A.Yu. Korchin, N.P. Merenkov
hep-ph