Probing cosmic anisotropy with gravitational waves as standard sirens

TL;DR

This study evaluates how well gravitational wave standard sirens can detect cosmic anisotropy, demonstrating their potential to constrain dipole amplitude and direction with upcoming GW detector data.

Contribution

It provides a systematic analysis of the capability of future GW detectors to probe cosmic anisotropy using standard sirens, highlighting their effectiveness in constraining dipole parameters.

Findings

Cosmic isotropy can be rejected at 3σ with MBHB models if dipole amplitude exceeds certain thresholds.

Einstein Telescope can constrain dipole direction within 20% at 3σ with at least 200 standard sirens.

Deci-Hertz Interferometer can constrain dipole direction within 10% at 3σ with over 100 standard sirens.

Abstract

The gravitational wave (GW) as a standard siren directly determines the luminosity distance from the gravitational waveform without reference to the specific cosmological model, of which the redshift can be obtained separately by means of the electromagnetic counterpart like GW events from binary neutron stars and massive black hole binaries (MBHBs). To see to what extent the standard siren can reproduce the presumed dipole anisotropy written in the simulated data of standard siren events from typical configurations of GW detectors, we find that (1) for the Laser Interferometer Space Antenna with different MBHB models during five-year observations, the cosmic isotropy can be ruled out at $3\sigma$ confidence level (C.L.) and the dipole direction can be constrained roughly around $20\%$ at $2\sigma$ C.L., as long as the dipole amplitude is larger than $0.03$, $0.06$ and $0.025$ for MBHB models Q3d, pop III and Q3nod with increasing constraining ability, respectively; (2) for Einstein Telescope with no less than $200$ standard siren events, the cosmic isotropy can be ruled out at $3\sigma$ C.L. if the dipole amplitude is larger than $0.06$, and the dipole direction can be constrained within $20\%$ at $3\sigma$ C.L. if the dipole amplitude is near $0.1$; (3) for the Deci-Hertz Interferometer Gravitational wave Observatory with no less than $100$ standard siren events, the cosmic isotropy can be ruled out at $3\sigma$ C.L. for dipole amplitude larger than $0.03$ , and the dipole direction can even be constrained within $10\%$ at $3\sigma$ C.L. if the dipole amplitude is larger than $0.07$. Our work manifests the promising perspective of the constraint ability on the cosmic anisotropy from the standard siren approach.