Test Gravitational-Wave Polarizations with Space-Based Detectors

TL;DR

This paper assesses how space-based gravitational wave detectors can identify non-tensor polarization modes in gravitational waves, revealing parameter estimation asymmetries and correlations that impact mode discrimination.

Contribution

It introduces a comprehensive Bayesian and Fisher matrix analysis of non-tensor modes using complete inspiral waveforms and explores the impact of a new LISA-Taiji network configuration.

Findings

Asymmetry in vector-mode parameter estimation at different inclination angles

Strong correlations between scalar-mode parameters limit independent estimation

Phase offset in the LISA-Taiji network has negligible effect on data analysis

Abstract

In this work, we systematically investigate the capability of space-based gravitational wave detectors in constraining parameters of non-tensor polarization modes. Using Bayesian inference and Fisher Information Matrix methods, we analyze gravitational wave signals from the inspiral phase of supermassive binary black hole mergers. By starting with time-domain signals and applying Fourier transforms, we avoid the use of the stationary phase approximation. We found an asymmetry in the estimation of the vector-mode parameter $\alpha_x$ at inclination angles $\iota = 0$ and $\iota = \pi$, which has not been explicitly pointed out in previous studies. We also observe strong correlations between scalar-mode parameters, $\alpha_b$ and $\alpha_l$, which currently limit their independent estimation. These findings underscore the importance of using complete inspiral-merger-ringdown waveforms to enhance the ability to distinguish the non-tensor polarization modes. Finally, we employ a new LISA-Taiji network configuration, in which the orientation of spacecrafts of Taiji maintains a fixed phase offset relative to these of LISA. Under the adiabatic approximation and the assumption of equal arms, this phase is found to have no significant effect on data analysis.