Distinguishing Monochromatic Signals in LISA and Taiji: Ultralight Dark Matter versus Gravitational Waves

TL;DR

This paper proposes a method using null-response channels in space-based gravitational wave detectors to distinguish between signals from ultralight dark matter and gravitational waves, enhancing the analysis capabilities of missions like LISA and Taiji.

Contribution

It introduces a novel diagnostic approach utilizing null-response channels to differentiate ULDM signals from GWs in space-based interferometers.

Findings

ULDM signals respond to the NRC at high frequencies

GWs remain undetected by the NRC from specific directions

The method enables discrimination between ULDM and GWs

Abstract

Ultralight dark matter (ULDM) is an attractive candidate for cold dark matter, one of the main mysterious components of the Universe. Recent studies suggest that gravitational-wave (GW) laser interferometers can also detect bosonic ULDM fields, which would produce monochromatic signals resembling those from gravitational waves (GWs). Distinguishing between these potential origins therefore would be essential. In this work, we develop a method to address this challenge for space-based GW interferometers (such as LISA and Taiji) by utilizing the null-response channel (NRC) in interferometric combinations, a channel constructed to have zero response to a specific type of source from a given direction. We find that while the GW NRC remains blind to GWs from a specific direction, it still responds to ULDM, particularly at frequencies above the interferometer's critical frequency. The ULDM NRC exhibits similar behavior. Based on these observations, we outline a test procedure to discriminate between signal origins. Our method provides a new diagnostic tool for analyzing monochromatic signals in space-based GW interferometers, potentially expanding the scientific scope of future missions.