Decay estimates for the wave and Dirac equations with a magnetic   potential
  We study the dispersive properties of the wave equation and the massless Dirac equation in three space dimensions, perturbed with electromagnetic potentials. The potentials are assumed to be small but may be rough. For both equations, we prove a dispersive estimate of the form |u(t,x)|< C/t. The constant C can be estimated in terms of a weighted H^s norm of the data, for suitable values of s. As a consequence of our method of proof, we establish the limiting absorption principle for the massless Dirac operator perturbed with a small, rough matrix potential. 
Piero D'Ancona, Luca Fanelli