Prospects of Indirect Detection of Dark Matter via Primordial Black Hole Induced Gravitational Waves

TL;DR

This paper explores how gravitational waves generated by primordial black holes can serve as a new way to detect and understand dark matter production in the early universe, especially in scenarios where PBHs dominate the cosmological dynamics.

Contribution

It provides a comprehensive analysis of dark matter production mechanisms in PBH-dominated cosmology and highlights the potential of gravitational wave observations as independent probes of dark matter properties.

Findings

GW observations can probe heavy DM with small interactions.

Thermal freeze-in can offset PBH-sourced DM underabundance.

GW and indirect detection explore complementary DM parameter spaces.

Abstract

Primordial black holes (PBHs), produced in the early Universe, can source a stochastic background of induced gravitational waves (GWs) and provide a non-thermal origin for dark matter (DM). We investigate DM production in a PBH-dominated cosmological framework, including contributions from PBH evaporation, gravitational production, and thermal freeze-in and freeze-out mechanisms, and determine the regions consistent with the observed DM relic abundance. We find that thermal freeze-in can compensate for the underabundance of PBH-sourced DM, while indirect detection remains largely insensitive due to the feeble interaction strength, making future GW observatories such as LISA and the Einstein Telescope (ET) unique probes of this scenario. For freeze-out DM, indirect detection experiments constrain regions with relatively large annihilation cross-sections, whereas GW observations probe complementary regions with heavier DM masses and smaller interaction strengths. Consequently, the same DM parameter space cannot be simultaneously probed by both indirect detection searches and GW missions. These results establish GW observations as a powerful and independent probe of DM production in PBH-dominated cosmologies, opening a new observational window into DM properties and the thermal history of the pre-BBN Universe.