## Abstract

We study the spin of primordial black holes produced by the collapse of large inhomogeneities in the early universe. Since such primordial black holes originate from peaks, that is, from maxima of the local overdensity, we resort to peak theory to obtain the probability distribution of the spin at formation. We show that the spin is a first-order effect in perturbation theory: it results from the action of first-order tidal gravitational fields generating first-order torques upon horizon-crossing, and from the asphericity of the collapsing object. Assuming an ellipsoidal shape, the typical value of the dimensionless parameter a_{s}=S/G_{N} M^{2}, where S is the spin and M is the mass of the primordial black hole, is about (Ω_{dm}/π) σ_{δ}1-γ^{2}. Here, σ^{2δ } is the variance of the overdensity at horizon crossing, Ω_{dm} measures the current abundance of the dark matter and the parameter γ is a measure of the width of the power spectrum giving rise to primordial black holes. One has γ=1 for monochromatic spectra. For these narrow spectra, the suppression arises because the velocity shear, which is strongly correlated with the inertia tensor, tends to align with the principal axis frame of the collapsing object. Typical values of a_{s} are at the percent level.

Original language | English |
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Article number | 018 |

Journal | Journal of Cosmology and Astroparticle Physics |

Volume | 2019 |

Issue number | 5 |

DOIs | |

State | Published - 13 Apr 2019 |

## Keywords

- physics of the early universe
- primordial black holes

## All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics