Axion Decay in a Constant Electromagnetic Background Field and at Finite   Temperature using World-line Methods
  We investigate the radiative decay of the axion into two photons in an external electromagnetic field to one loop order. Our approach is based on the world-line formalism, which is very suitable to take into account the external field to all orders. Afterwards we discuss how the calculation could be generalized to finite temperature. 
Michael Haack (Halle U.), Michael G. Schmidt (Heidelberg U.)