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 as=S/GN M2, where S is the spin and M is the mass of the primordial black hole, is about (Ωdm/π) σδ1-γ2. Here, σ2javax.xml.bind.JAXBElement@6e6a5295 is the variance of the overdensity at horizon crossing, Ωdm 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 as are at the percent level.

The initial spin probability distribution of primordial black holes / Luca, V. D.; Desjacques, V.; Franciolini, G.; Malhotra, A.; Riotto, A.. - In: JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS. - ISSN 1475-7516. - 2019:5(2019), pp. 018-018. [10.1088/1475-7516/2019/05/018]

The initial spin probability distribution of primordial black holes

Franciolini G.;Riotto A.
2019

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 as=S/GN M2, where S is the spin and M is the mass of the primordial black hole, is about (Ωdm/π) σδ1-γ2. Here, σ2javax.xml.bind.JAXBElement@6e6a5295 is the variance of the overdensity at horizon crossing, Ωdm 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 as are at the percent level.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1643182
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