Gravitational waves from a universe filled with primordial black holes

Theodoros Papanikolaou (1) , Vincent Vennin (1) , David Langlois (1)

1 APC (UMR_7164) - AstroParticule et Cosmologie

Ultra-light primordial black holes, with masses m PBH < 109g, evaporate before big-bang nucleosynthesis and can therefore not be directly constrained. They can however be so abundant that they dominate the universe content for a transient period (before reheating the universe via Hawking evaporation). If this happens, they support large cosmological fluctuations at small scales, which in turn induce the production of gravitational waves through second-order effects. Contrary to the primordial black holes, those gravitational waves survive after evaporation, and can therefore be used to constrain such scenarios. In this work, we show that for induced gravitational waves not to lead to a backreaction problem, the relative abundance of black holes at formation, denoted ΩPBH,f, should be such that ΩPBH,f < 10-4(m PBH/109g)-1/4. In particular, scenarios where primordial black holes dominate right upon their formation time are all excluded (given that m PBH > 10 g for inflation to proceed at ρ1/4 < 1016 GeV). This sets the first constraints on ultra-light primordial black holes.

Mots clés: physics of the early universe; gravitational waves / theory; primordial black holes; black hole: primordial; black hole: mass; gravitational radiation: induced; nucleosynthesis: big bang; formation: time; black hole: formation; black hole: evaporation; back reaction; space-time: fluctuation; reheating; inflation; evaporation; gravitational radiation: emission; power spectrum: tensor; power spectrum; matter: power spectrum; perturbation: scalar; tensor: energy-momentum; energy: density; gauge

Domaines: Astrophysique [astro-ph]; Relativité Générale et Cosmologie Quantique [gr-qc]; Physique des Hautes Energies - Théorie [hep-th]

Theodoros Papanikolaou, Vincent Vennin, David Langlois. Gravitational waves from a universe filled with primordial black holes. JCAP, 2021, 03, pp.053. ⟨10.1088/1475-7516/2021/03/053⟩. ⟨hal-02999527⟩