Quantum gravitational optics in the field of a gravitomagnetic monopole
  Vacuum polarization in QED in a background gravitational field induces interactions which {\it effectively} modify the classical picture of light rays as the null geodesics of spacetime. After a short introduction on the main aspects of the quantum gravitational optics, as a nontrivial example, we study this effect in the background of NUT space characterizing the spacetime of a spherical mass endowed with a gravitomagnetic monopole charge, the so called NUT factor. 
N. Ahmadi, S. Khoeini-Moghaddam and M. Nouri-Zonoz