THERMALLY-INDUCED PHOTON SPLITTING

We calculate thermal corrections to the non-linear QED effective actio n for low-energy photon interactions in a background electromagnetic f ield, The high-temperature expansion shows that at T much greater than in the vacuum contribution is exactly cancelled to all orders in the external field except for a non-trivial two-point function contributio n. The high-temperature expansion derived reveals a remarkable cancell ation of infrared sensitive contributions. As a result photon-splittin g in the presence of a magnetic field is suppressed in the presence of an electron-positron QED-plasma at very high temperatures. In a cold and dense plasma a similar suppression takes place. At the same time C ompton scattering dominates for weak fields and the suppression is rar ely important in physical situations. (C) 1998 Elsevier Science B.V. A ll rights reserved.