[Paper Review] Primordial black holes and their gravitational-wave signatures

E. Bagui, Sébastien Clesse+18 more|arXiv (Cornell University)|Oct 30, 2023

Cosmology and Gravitation Theories31 citations

TL;DR

The paper reviews primordial black holes (PBHs) and their gravitational-wave signatures, outlining formation, evolution, merger rates, and detectability with LISA, including stochastic backgrounds and cross-correlations with large-scale structure.

ABSTRACT

In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyse and combine the latest developments in order to perform end-to-end calculations of the various gravitational wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space.

Motivation & Objective

• Survey PBH formation and evolution mechanisms across inflationary and non-inflationary models.
• Compute end-to-end gravitational-wave signatures from PBHs, including mergers and stochastic backgrounds.
• Assess PBH GW detectability with LISA and explore distinguishing features from stellar-origin BHs.
• Discuss current observational limits on PBH abundance in light of GW data and other probes.

Proposed method

• Synthesize recent theoretical models for PBH formation, including single-field and multi-field inflation, and non-inflationary mechanisms.
• Incorporate advances in PBH mass distribution, clustering, and merger-rate calculations (early and late binaries).
• Evaluate GW signatures from PBH scenarios, including individual mergers, hyperbolic encounters, and second-order curvature-induced backgrounds.

Experimental results

Research questions

• RQ1 What are the primary PBH formation channels and how do they shape the mass and spin distributions?
• RQ2 How do PBH merger rates and gravitational-wave signatures depend on formation, clustering, and astrophysical environments?
• RQ3 What GW signatures (individual events, stochastic backgrounds) uniquely distinguish PBHs from stellar-origin black holes?
• RQ4 What is the detectability of PBH-related GW signals with LISA across different mass ranges and redshifts?
• RQ5 How do cross-correlations with large-scale structure constrain PBH abundance and scenarios?

Key findings

• PBHs can produce diverse GW signatures via mergers, hyperbolic encounters, and second-order curvature-induced backgrounds.
• LISA bandwidth (~millihertz) enables probing PBH mergers from 10^3–10^4 solar masses to high redshift and potential subsolar channels.
• Recent modeling advances link PBH formation, clustering, and merger rates to specific GW observables and their amplitudes.
• Cross-correlations between GW data and large-scale structure offer a pathway to constrain PBH abundance.
• Stochastic GW backgrounds from PBH-related perturbations may be within LISA’s reach, depending on the PBH population.
• The review presents a living framework with ongoing bi-yearly updates to track rapid progress in PBH GW signatures.