Process ν → νγ in strong magnetic field with allowance for posironium contribution to photon dispersion

We have studied the radiative decay of neutrinos with relatively high energies E a parts per thousand << m (e) in a strong magnetic field taking into account the effect of a bound electron-positron pair (positronium) on photon dispersion. The allowance for the positronium contribution to the polarization operator of the photon substantially modifies the dispersion relation for the photon and the amplitude of the process in the vicinity of the cyclotron resonance. It is shown that the probability of the nu -> nu I-3 process considerably increases when the positronium contribution is taken into account.