Description
We study the propagation of high-frequency electromagnetic waves in curved spacetime in the presence of axion-like scalar fields. We employ the spinoptics approximation and extend the covariant effective action approach recently developed by Frolov to incorporate axion–photon coupling. The resulting spinoptics equations are solved in the background of a Schwarzschild black hole dressed with an axion field, with particular emphasis on the appropriate construction of a complex null tetrad associated with null rays in the presence of the axion. We show that axions affect photon trajectories differently from gravitational fields.