Detecting Subsolar-Mass Primordial Black Holes in Extreme Mass-Ratio Inspirals with LISA and Einstein Telescope

TL;DR

This paper proposes using extreme mass-ratio inspirals observed by LISA and Einstein Telescope to detect primordial black holes with masses below that of the Sun, offering a new way to probe dark matter and early universe physics.

Contribution

It demonstrates that future gravitational wave detectors can measure subsolar-mass black holes with high precision, enabling the potential discovery of primordial black holes as dark matter candidates.

Findings

Subsolar-mass black holes can be detected up to hundreds of Mpc with LISA.

Third-generation detectors can observe these black holes at gigaparsec distances.

High-confidence measurements of subsolar-mass objects are achievable with upcoming detectors.

Abstract

Primordial black holes possibly formed in the early universe could provide a significant fraction of the dark matter and would be unique probes of inflation. A smoking gun for their discovery would be the detection of a subsolar mass compact object. We argue that extreme mass-ratio inspirals will be ideal to search for subsolar-mass black holes not only with LISA but also with third-generation ground-based detectors such as Cosmic Explorer and the Einstein Telescope. These sources can provide unparalleled measurements of the mass of the secondary object at subpercent level for primordial black holes as light as ${\cal O}(0.01)M_\odot$ up to luminosity distances around hundred megaparsec and few gigaparsec for LISA and Einstein Telescope, respectively, in a complementary frequency range. This would allow claiming, with very high statistical confidence, the detection of a subsolar-mass black hole, which would also provide a novel (and currently undetectable) family of sources for third-generation detectors.