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

The process of photon splitting γ→γγ in a strong magnetic field is investigated both below and above the pair creation threshold. Contrary to the statement by Baier et al., the “allowed” channel γ‖→γ⊥γ⊥ is shown not to be a comprehensive description of splitting in the strong field because the “forbidden” channel γ‖→γ‖γ⊥ 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.