Electric-magnetic duality and renormalization in curved spacetimes
  We point out that the duality symmetry of free electromagnetism does not hold in the quantum theory if an arbitrary classical gravitational background is present. The symmetry breaks in the process of renormalization, as also happens with conformal invariance. We show that a similar duality-anomaly appears for a massless scalar field in $1+1$ dimensions. 
Ivan Agullo, Aitor Landete, Jose Navarro-Salas
gr-qc hep-th