Particle production in a gravitational wave background

TL;DR

This paper investigates how gravitational waves can produce massless particles, like photons, by calculating the scalar field production rate in a gravitational wave background, revealing potential wave attenuation effects.

Contribution

It provides a detailed calculation of massless scalar particle production by gravitational waves, extending the understanding of particle creation in curved spacetime.

Findings

Scalar field has a non-zero vacuum expectation value in a gravitational wave background

Gravitational waves can produce massless scalar particles without exponential suppression

Potential implications for gravitational wave attenuation mechanisms

Abstract

We study the possibility that massless particles, such as photons, are produced by a gravitational wave. That such a process should occur is implied by tree-level, Feynman diagrams such as two gravitons turning into two photons i.e. $g + g \rightarrow \gamma + \gamma$. Here we calculate the rate at which a gravitational wave creates a massless, scalar field. This is done by placing the scalar field in the background of a plane gravitational wave and calculating the 4-current of the scalar field. Even in the vacuum limit of the scalar field it has a non-zero vacuum expectation value (similar to what occurs in the Higgs mechanism) and a non-zero current. We associate this with the production of scalar field quanta by the gravitational field. This effect has potential consequences for the attenuation of gravitational waves since the massless field is being produced at the expense of the gravitational field. This is related to the time-dependent Schwinger effect, but with the electric field replaced by the the gravitational wave background and the electron/positron field quanta replaced by massless scalar "photons". Since the produced scalar quanta are massless there is no exponential suppression as occurs in the Schwinger effect due to the electron mass.