Primordial black holes from a tiny bump/dip in the inflaton potential
Abstract
Scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. A bumplike feature behaves like a local speedbreaker and lowers the speed of the scalar field, thereby locally enhancing the scalar power spectrum. A bumplike feature emerges naturally if the base inflaton potential V_{b}(phi) contains a local correction term such as V_{b}(phi)[1+ɛ(phi)] at phi=phi_{0}. The presence of such a localised correction term at phi_{0} leads to a large peak in the curvature power spectrum and to an enhanced probability of black hole formation. Remarkably this does not significantly affect the scalar spectral index n_{S} and tensor to scalar ratio r on CMB scales. Consequently such models can produce higher mass primordial black holes (M_{PBH}>= 1 M_{solar}) in contrast to models with `near inflectionpoint potentials' in which generating higher mass black holes severely affects n_{S} and r. With a suitable choice of the base potential—such as the string theory based (KKLT) inflation or the αattractor models—the amplification of primordial scalar power spectrum can be as large as 10^{7} which leads to a significant contribution of primordial black holes (PBHs) to the dark matter density today, f_{PBH} = Ω_{0, PBH}/Ω_{0,DM} ~ O(1). Interestingly, our results remain valid if the bump is replaced by a dip. In this case the base inflaton potential V_{b}(phi) contains a negative local correction term such as V_{b}(phi)[1ɛ(phi)] at phi=phi_{0} which leads to an enhanced probability of PBH formation. We conclude that primordial black holes in the mass range 10^{17} M_{solar} <= M_{PBH} <= 100 M_{solar} can easily form in single field inflation in the presence of small bumplike and diplike features in the inflaton potential.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 April 2020
 DOI:
 10.1088/14757516/2020/04/007
 arXiv:
 arXiv:1911.00057
 Bibcode:
 2020JCAP...04..007M
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 33 pages, 15 figures, Results extended to include a dip in the potential, Additional comments and references, Accepted for publication in JCAP