The source-free Maxwell action is invariant under electric-magnetic duality rotations in arbitrary spacetimes. This leads to a conserved classical Noether charge. We show that this conservation law is broken at the quantum level in the presence of a background classical gravitational field with a nontrivial Chern-Pontryagin invariant, in parallel with the chiral anomaly for massless Dirac fermions. Among the physical consequences, the net polarization of the quantum electromagnetic field is not conserved.
Publication Source (Journal or Book title)
Physical Review Letters
Agullo, I., Del Rio, A., & Navarro-Salas, J. (2017). Electromagnetic Duality Anomaly in Curved Spacetimes. Physical Review Letters, 118 (11) https://doi.org/10.1103/PhysRevLett.118.111301