Large-Scale Structure with Gravitational Waves I: Galaxy Clustering

TL;DR

This paper investigates how a gravitational wave background influences galaxy clustering observations, calculating the effects at linear order and assessing their significance relative to scalar contributions.

Contribution

It provides the first detailed calculation of galaxy clustering distortions caused by gravitational waves, including all relativistic effects at linear order.

Findings

Effects are most significant at low multipoles (l=2-5).

Effects are suppressed by over six orders of magnitude compared to scalar contributions.

Second-order effects involve distortion of tracer correlation functions by gravitational waves.

Abstract

Observed angular positions and redshifts of large-scale structure tracers such as galaxies are affected by gravitational waves through volume distortion and magnification effects. Thus, a gravitational wave background can in principle be probed through clustering statistics of large-scale structure. We calculate the observed angular clustering of galaxies in the presence of a gravitational wave background at linear order including all relativistic effects. For a scale-invariant spectrum of gravitational waves, the effects are most significant at the smallest multipoles (2 <= l <= 5), but typically suppressed by six or more orders of magnitude with respect to scalar contributions for currently allowed amplitudes of the inflationary gravitational wave background. We also discuss the most relevant second-order terms, corresponding to the distortion of tracer correlation functions by gravitational waves. These provide a natural application of the approach recently developed in arXiv:1204.3625.