Electromagnetic wave propagation in static black hole spacetimes: an effective refractive index description in Schwarzschild geometry
This paper presents a fully covariant and gauge-invariant formulation of electromagnetic wave propagation in static black hole spacetimes that reduces both axial and polar sectors to a unified master equation, enabling the derivation of a closed-form, position- and frequency-dependent effective refractive index in Schwarzschild geometry to provide an intuitive optical framework for analyzing gravitational effects on wave dynamics.