Probing nontensorial gravitational waves with a next-generation ground-based detector network

TL;DR

This paper evaluates how a future ground-based gravitational wave detector network can detect non-tensorial polarization modes, testing alternative gravity theories through simulations of neutron star mergers.

Contribution

It introduces a method for localizing gravitational wave signals and constructing null streams to detect scalar and vector modes in a next-generation detector network.

Findings

Detection thresholds for scalar and vector modes at 5σ confidence are 0.045 and 0.014 respectively for a single event.

For a 10-year observing run, the detection limits are 0.05 and 0.02 for scalar and vector modes.

A few strong events could significantly improve the sensitivity to non-tensorial polarizations.

Abstract

In General Relativity, there are only two polarizations for gravitational waves. However, up to six polarizations are possible in a generic metric theory of gravity. Therefore, measuring the polarization content of gravitational waves provides an efficient way to test theories of gravity. We analyze the sensitivity of a next-generation ground-based detector network to nontensorial polarizations. We present our method to localize GW signals in the time-frequency domain and construct the model-independent null stream for events with known sky locations. We obtain results based on simulations of binary neutron star mergers in a six-detector network. For a single event at a luminosity distance $D_L=100 \, {\rm Mpc}$, at $5\sigma$ confidence, the smallest amplitude for detection of scalar and vector modes relative to tensor modes are respectively $A_{s}=0.045 $ and $A_{v}=0.014 $. For multiple events in an averaged observing run of 10 years, the detection limits at $5\sigma$ confidence are $A_s=0.05$ and $A_v=0.02$. If we are fortunate, a few strong events might significantly improve the limits.