Gravitational waves in the modified gravity

TL;DR

This paper investigates gravitational waves within a modified gravity framework involving a scalar field, revealing additional polarization modes beyond those predicted by general relativity, including scalar longitudinal and breathing modes.

Contribution

It introduces a specific modified gravity model with a scalar field and analyzes the resulting gravitational wave polarization modes, highlighting new scalar modes not present in general relativity.

Findings

Identification of two additional scalar polarization modes.

Analysis of how scalar field potential affects gravitational wave modes.

Extension of gravitational wave polarization analysis to modified gravity theories.

Abstract

We have taken a modified version of the Einstein Hilbert action, $ f(R, T^\phi) $ gravity under consideration, where $T^\phi$ is the energy-momentum tensor trace for the scalar field under consideration. The structural behaviour of the scalar field considered varies with the form of the potential. The number of polarization modes of gravitational waves in modified theories has been studied extensively for the corresponding fields. There are two additional scalar modes, in addition to the usual two transverse-traceless tensor modes found in general relativity: a massive longitudinal mode and a massless transverse mode (the breathing mode).