Quantum gravitational optics: Effective Raychaudhuri equation

TL;DR

This paper investigates how quantum electrodynamics vacuum polarization in a gravitational field modifies classical light ray behavior, leading to effective superluminal photon velocities and altered optical properties.

Contribution

It introduces a perturbative deformation of the Raychaudhuri equation accounting for vacuum polarization effects on photon propagation in curved spacetime.

Findings

Vacuum polarization induces modifications to optical scalars.

Photon velocities can become superluminal due to quantum effects.

The study provides a framework for quantum gravitational optics.

Abstract

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. These interactions violate the strong equivalence principle and affect the propagation of light leading to superluminal photon velocities. Taking into account the QED vacuum polarization, we study the propagation of a bundle of rays in a background gravitational field. To do so we consider the perturbative deformation of Raychaudhuri equation through the influence of vacuum polarization on photon propagation. We analyze the contribution of the above interactions to the optical scalars namely, shear, vorticity and expansion using the Newman-Penrose formalism.