Probing non-tensorial polarizations of stochastic gravitational-wave backgrounds with ground-based laser interferometers

TL;DR

This paper explores how ground-based laser interferometers can detect and distinguish additional polarization modes of stochastic gravitational-wave backgrounds, which are predicted by extended theories of gravity beyond general relativity.

Contribution

It demonstrates that multiple detectors can effectively separate and measure different polarization modes of gravitational waves, enhancing tests of alternative gravity theories.

Findings

Multiple detectors can separate polarization modes.

Detectors have similar sensitivity to all polarization modes.

Method enables testing of extended gravitational theories.

Abstract

In a general metric theory of gravitation in four dimensions, six polarizations of a gravitational wave are allowed: two scalar and two vector modes, in addition to two tensor modes in general relativity. Such additional polarization modes appear due to additional degrees of freedom in modified theories of gravitation or theories with extra dimensions. Thus, observations of gravitational waves can be utilized to constrain the extended models of gravitation. In this paper, we investigate detectability of additional polarization modes of gravitational waves, particularly focusing on a stochastic gravitational-wave background, with laser-interferometric detectors on the Earth. We found that multiple detectors can separate the mixture of polarization modes in detector outputs, and that they have almost the same sensitivity to each polarization mode of stochastic gravitational-wave background.