# Intermediate mass-ratio inspirals in a dense dark-matter environment: Effects of the initial dark-matter distribution

## TL;DR

This study explores how initial dark-matter distributions, shaped by accretion and merger history, influence gravitational wave signals from intermediate mass-ratio inspirals, with implications for detection by future space-based observatories.

## Contribution

It introduces models of dark-matter initial conditions considering accretion and mergers, and analyzes their impact on gravitational wave dephasing in inspiral signals.

## Key findings

- Dark-matter accretion reduces gravitational wave dephasing, especially at high mass ratios.
- Prior merger history affects the dephasing, more so at lower mass ratios.
- Environmental effects remain detectable by future space-based gravitational wave detectors.

## Abstract

Recent work has shown the possibility of detecting dense dark-matter distributions surrounding intermediate or extreme mass-ratio inspirals through gravitational waves using LISA. Modeling these systems requires evolving the coupled dynamics of the binary and the dark matter. This also requires setting reasonable initial conditions for the dark-matter distribution, which itself relies upon understanding the formation history of these systems. In this paper, we investigate how two aspects of these systems' formation histories shape the dark-matter distribution: accretion onto the primary and prior merger events. We model accretion by introducing a minimum allowed angular momentum of dark-matter particles, which removes such particles that would have been accreted by the primary. When simulating an inspiral within such a distribution, we find a smaller dephasing of the gravitational-wave signal from a vacuum binary as compared to an inspiral without such a cutoff, particularly for more extreme mass-ratios. We also simulate an inspiral which takes place within a dark-matter distribution that remains after a prior merger. We find that the decrease in dephasing from vacuum binaries when compared to the prior inspiral is most significant for less extreme mass-ratios. Nevertheless, the environmental effects from the dark matter for these different cases of initial data are still expected to be measurable by future space-based detectors.