Constraints on primordial black holes

Area of Science:

• Cosmology and Astrophysics
• Particle Physics
• General Relativity

Background:

• Primordial black holes (PBHs) are hypothetical black holes formed in the early Universe.
• Their abundance and mass distribution are poorly constrained.
• PBHs are potential candidates for dark matter and could influence cosmic structure formation.

Purpose of the Study:

• To update and consolidate constraints on the fraction of the Universe that could be composed of PBHs.
• To examine PBH constraints across a broad mass range (10^-5 to 10⁵⁰ g).
• To discuss the implications of PBHs for dark matter, gravitational wave events, and early Universe cosmology.

Main Methods:

• Analysis of constraints from Hawking radiation, Big Bang nucleosynthesis, and cosmic microwave background (CMB) for low-mass PBHs (<10¹⁵ g).
• Inclusion of constraints from gravitational lensing, dynamical effects, large-scale structure, accretion, and gravitational waves for high-mass PBHs (>10¹⁵ g).
• Consideration of indirect constraints from primordial density fluctuations and CMB distortions, and the impact of extended mass functions.

Main Results:

• Updated constraints on the abundance of PBHs across the mass range 10^-5 to 10⁵⁰ g.
• Identification of key observational and theoretical uncertainties affecting current constraints.
• Discussion of how PBHs could contribute to dark matter, LIGO/Virgo events, and structure seeds, even with a small DM fraction.

Conclusions:

• PBHs remain a viable, albeit constrained, component of the Universe.
• Updated constraints refine our understanding of PBH formation and evolution.
• PBHs offer a unique window into the early Universe and fundamental physics.