Overlap reduction function for gravitational wave detectors in an expanding Universe

TL;DR

This paper investigates how the accelerating expansion of the Universe influences the overlap reduction functions of gravitational wave detectors, revealing that cosmic expansion can enhance detection sensitivity, especially for closely separated pulsar pairs.

Contribution

It introduces a novel analysis of overlap reduction functions in de-Sitter space-time, accounting for the effects of cosmic expansion on gravitational wave detection.

Findings

Expansion can enhance overlap reduction functions for close detector pairs.

Cosmological constant influences gravitational wave detection sensitivity.

Effect is significant for nanohertz gravitational waves from pulsar pairs.

Abstract

Since it was confirmed two decades ago that the expansion of the Universe is accelerating, it would be of theoretical interests to figure out what is the influence from cosmological constant on detection of stochastic gravitational wave background. This paper studies the overlap reduction functions in de-Sitter space-time for a pair of one-way tracking gravitational wave detectors. It is shown to be non-trivial in an expanding Universe, because the propagation of light along line of sight also has effect on the response of GW detectors. It is found that the expansion of the Universe can enhance the value of magnitude of the overlap reduction functions, when the detector pairs are close to each other. For nanohertz gravitational waves, this effect can dominate the values of overlap reduction functions when the galactic pulsar pairs are separated by milliarcsecond.