Photon splitting above the pair creation threshold in a strong magnetic field

The process of photon splitting gamma-->gamma gamma in a strong magnetic field is investigated both below and above the pair creation threshold. Contrary to the statement by Paler et al., the "allowed" channel gamma(parallel to)-->gamma(perpendicular to)gamma(perpendicular to) is shown not to be a comprehensive description of splitting in the strong field because the ''forbidden'' channel y(parallel to)-->gamma(parallel to)gamma(perpendicular to) is also essential. The partial amplitudes and the splitting probabilities are calculated taking account of the photon dispersion and large radiative corrections near the resonance. (C) 1998 Published by Elsevier Science B.V. All rights reserved.