Weak-field expansion for processes in a homogeneous background magnetic field - art. no. 105014

The weak-field expansion of the charged fermion propagator under a uniform magnetic field is studied. Starting from Schwinger's proper-time representa tion, we express the charged fermion propagator as an infinite series corre sponding to different Landau levels. This infinite series is then reorganiz ed according to the powers of the external field strength B. For illustrati on, we apply this expansion to gamma --> nu<(<nu>)over bar> and nu --> nu g amma decays, which involve charged fermions in the internal loop. The leadi ng and subleading magnetic-field effects to the above processes are compute d.