Probing Stochastic Ultralight Dark Matter with Space-based Gravitational-Wave Interferometers

TL;DR

This paper explores how space-based gravitational-wave interferometers can detect stochastic ultralight dark matter fields, potentially surpassing current limits and optimizing detector configurations for improved sensitivity.

Contribution

It systematically analyzes the sensitivity of space-based interferometers to ULDM, introduces the overlap reduction function for ULDM, and identifies optimal detector configurations for detection.

Findings

Space-based interferometers can probe new ULDM parameter space.

Uncorrelated detector signals are optimal for ULDM detection.

The study provides a framework for joint ULDM observations with future detectors.

Abstract

Ultralight particles are theoretically well-motivated dark matter candidates. In the vicinity of the solar system, these ultralight particles can be described as a superposition of plane waves, resulting in a stochastic field with sizable amplitude fluctuations on scales determined by the velocity dispersion of dark matter. In this work, we systematically investigate the sensitivity of space-based gravitational-wave interferometers to the stochastic ultralight dark matter (ULDM) field within the frequentist framework. We derive the projected sensitivity of a single detector using the time-delay interferometry. Our results show that space-based gravitational-wave interferometers have the potential to probe unconstrained regions in parameter space and improve the current limit on coupling strengths. Furthermore, we explore the sensitivity of a detector network and investigate the optimal configuration for ULDM detection. We introduce the overlap reduction function for ULDM, which quantifies the degree of correlation between the signals observed by different detectors. We find that the configuration, where the signals observed by two detectors are uncorrelated, is the optimal choice for ULDM detection due to a smaller chance of missing signal. This contrasts with the detection of stochastic gravitational-wave background, where the correlated configuration is preferred. Our results may provide useful insights for potential joint observations involving space-based gravitational-wave detectors like LISA and Taiji, as well as other ULDM detection networks operating in the coherence limit.