Refraction index analysis of light propagation in a colliding gravitational wave spacetime

TL;DR

This paper explores how light propagates in a complex spacetime formed by colliding gravitational waves, using the optical medium analogy to understand effects like horizons or singularities.

Contribution

It generalizes previous optical medium analyses from single to colliding gravitational waves, providing insights into photon behavior in nonlinear gravitational interactions.

Findings

Photon propagation is affected by nonlinear gravitational interactions.

Optical medium analogy captures effects like horizons or singularities.

Provides a simplified framework for complex gravitational phenomena.

Abstract

The optical medium analogy of a given spacetime was developed decades ago and has since then been widely applied to different gravitational contexts. Here we consider the case of a colliding gravitational wave spacetime, generalizing previous results concerning single gravitational pulses. Given the complexity of the nonlinear interaction of two gravitational waves in the framework of general relativity, typically leading to the formation of either horizons or singularities, the optical medium analogy proves helpful to simply capture some interesting effects of photon propagation.