Blueshift of light rays induced by gravitational wave memory effect

TL;DR

This paper investigates how gravitational wave memory effects in pp-wave spacetimes cause a permanent frequency shift in photons, impacting redshift measurements and potentially explaining supernova redshift anomalies.

Contribution

It demonstrates that gravitational wave memory induces a finite, path-dependent redshift effect on photons, offering new insights into gravitational wave-photon interactions.

Findings

Null geodesics crossing a pp-wave pulse exhibit an energy memory effect.

The effect produces a finite asymptotic shift in photon frequency.

This shift influences redshift measurements and may clarify supernova redshift data anomalies.

Abstract

The article deals with photon propagation in pp-wave spacetimes in the strong gravitational-wave regime and its consequences for redshift measurements. We show that null geodesics crossing a localized pp-wave pulse exhibit an energy memory effect, producing a finite asymptotic shift in the photon frequency measured by static observers. This path-dependent contribution acts directly on the redshift observable and may help account for divergent interpretations of supernova redshift data in the presence of intervening gravitational radiation.