Photon splitting in an ultrastrong magnetic field

We analyze the splitting of a photon with energy ω below the e+e− pair-production threshold in an ultrastrong magnetic field. We use the amplitudes found by employing the operator diagrammatic technique. In a field considerably above the critical values the process amplitudes become independent of the field strength. A study of the polarization operator of a photon in an external field of arbitrary strength in the energy range considered in the present investigation shows that there is only one set of polarizations of the initial and final photons for which the splitting amplitude is nonzero.