Gravitational Waves in Cold Dark Matter

TL;DR

This paper investigates how cold dark matter influences gravitational wave propagation, finding that effects are minimal and currently undetectable, but primordial wave spectra could, in principle, reveal dark matter properties.

Contribution

It provides a detailed analysis of dark matter's subtle effects on gravitational waves, highlighting the challenges in detecting these effects and their potential to inform dark matter characteristics.

Findings

Dark matter causes small, frequency-dependent modifications to gravitational wave speed.

Effects on primordial gravitational waves are suppressed or negligible.

Current detection methods are insufficient to observe these effects.

Abstract

We study the effects of cold dark matter on the propagation of gravitational waves of astrophysical and primordial origin. We show that the dominant effect of cold dark matter on gravitational waves from astrophysical sources is a small frequency dependent modification of the propagation speed of gravitational waves. However, the magnitude of the effect is too small to be detected in the near future. We furthermore show that the spectrum of primordial gravitational waves in principle contains detailed information about the properties of dark matter. However, depending on the wavelength, the effects are either suppressed because the dark matter is highly non-relativistic or because it contributes a small fraction of the energy density of the universe. As a consequence, the effects of cold dark matter on primordial gravitational waves in practice also appear too small to be detectable.