Primordial Black Holes from String Inflation

Cicoli, Michele; Diaz, Victor A.; Pedro, Francisco G.

doi:10.48550/arxiv.1803.02837

Cited by 22 publications

(41 citation statements)

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“…For quasi-inflection inflation instead it has been argued [9,13] that the super-horizon growth of R is due to entropy perturbations. Nevertheless, in agreement with the general analysis given in [8], it has also been [14][15][16][17] shown in different scenarios that the super-horizon growth of R can be explained uniquely in terms of the evolution of the background, so it is important to clarify if non adiabatic perturbations actually play any important role.…”

Section: Introductionsupporting

confidence: 73%

Are primordial black holes produced by entropy perturbations in single field inflationary models?

Vallejo-Peña

Romano

2019

J. Cosmol. Astropart. Phys.

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We show that in single field inflationary models the super-horizon evolution of curvature perturbations on comoving slices R, which can cause the production of primordial black holes (PBH), is not due to entropy perturbations, but to the background evolution effect on the conversion between entropy and curvature perturbations. We derive a general relation between the time derivative of comoving curvature perturbations and entropy perturbations, in terms of a conversion factor depending on the background evolution. Contrary to previous results derived in the uniform density gauge assuming the gradient term can be neglected on super-horizon scales, the relation is valid on any scale for any minimally coupled single scalar field model, also on sub-horizon scales where gradient terms are large.We apply it to the case of quasi-inflection inflation, showing that while entropy perturbations are decreasing, R can grow on super-horizon scales, due to a large increase of the conversion factor. This happens in the time interval during which a sufficiently fast decrease of the equation of state w transforms into a growing mode what in slow-roll models would be a decaying mode. The same mechanism also explains the super-horizon evolution of R in globally adiabatic systems, for which entropy perturbations vanish on any scale, such as ultra slow roll inflation and its generalizations.

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Section: Introductionsupporting

confidence: 73%

Are primordial black holes produced by entropy perturbations in single field inflationary models?

Vallejo-Peña

Romano

2019

J. Cosmol. Astropart. Phys.

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“…Whilst such a potential can certainly be manufactured within effective field theory, ultimately its shape -and robustness against quantum corrections -would have to be explained within a fundamental theory, like string theory. For example, an attempt towards embedding this model within string theory via fine-tuned string-loop corrections in fibre inflation has been made very recently in [12], although it has not yet proved possible to fine-tune a setup such that cosmological 1 A possible obstacle for PBH's as Dark Matter in this mass range is the constraints arise due to capture of PBH by stars during their formation which may limit the PBH abundance to no more than one percent of the Dark Matter density [6].…”

Section: Introductionmentioning

confidence: 99%

“…All time dependent quantities in the expressions above should be evaluated at the time of horizon crossing11 N hc where the comoving pivot scale k = k * leaves the horizon (a hc H hc ) −1 . To determine the time of horizon crossing, we first use the numerical solutions to the FRW background equations (3.4) to describe the evolution of the Hubble slow-roll parameters in (3.9) in terms of the number of e-folds N and then impose the following measurements and bounds on the CMB observables from12 Planck 2015 (at k * = 0.05 Mpc −1 and 68% CL for TT+lowP+BAO)[47], ln(10 10 A s ) = 3.093 ± 0.034, n s = 0.9673 ± 0.0043, α s = −0.0125 ± 0.0091, r < 0.166 (the Planck/KEK combined analysis gives r < 0.07),(3.11)…”

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confidence: 99%

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Mechanisms for Primordial Black Hole Production in String Theory

Özsoy,

Parameswaran,

Tasinato

et al. 2018

Preprint

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We consider mechanisms for producing a significant population of primordial black holes (PBHs) within string inspired single field models of inflation. The production of PBHs requires a large amplification in the power spectrum of curvature perturbations between scales associated with CMB and PBH formation. In principle, this can be achieved by temporarily breaking the slow-roll conditions during inflation. In this work, we identify two string setups that can realise this process. In string axion models of inflation, subleading non-perturbative effects can superimpose steep cliffs and gentle plateaus onto the leading axion potential. The cliffs can momentarily violate the slow-roll conditions, and the plateaus can lead to phases of ultra slow-roll inflation. We thus achieve a string motivated model which both matches the Planck observations at CMB scales and produces a population of light PBHs, which can account for an order one fraction of dark matter. In DBI models of inflation, a sharp increase in the speed of sound sourced by a steep downward step in the warp factor can drive the amplification. In this scenario, discovery of PBHs could indicate non-trivial dynamics in the bulk, such as flux-antibrane annihilation at the tip of a warped throat.

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“…In these backgrounds, the amplitude of ζ displays a rapid growth for wavelengths larger than H −1 . This has propelled considerably interest in studying the effects of transient non-attractor periods during inflation as a way of generating primordial black holes (PBHs) [21][22][23][24][25][26][27][28][29][30][31][32][33][34]. For the same reasons, the status of non-Gaussianity in non-attractor models has remained a matter of great interest.…”

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confidence: 99%

Unifying attractor and non-attractor models of inflation under a single soft theorem

Bravo¹,

Palma²

2020

Preprint

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We derive the bispectrum's squeezed limit of primordial curvature perturbations in canonical single field inflation valid to all orders in slow-roll parameters. Our derivation relies exclusively on the diffeomorphism invariance of canonical single field inflation, and does not require taking into account de Sitter isometries or shift symmetries of the ultraviolet theory in which inflation is build upon. Our result consists in the standard Maldacena's consistency relation (proportional to the spectral index of the power spectrum) plus additional terms containing time derivatives of the power spectrum. An important consequence of our result is the conclusion that a non-attractor phase (e.g. ultra slow roll phase) cannot generate large non-Gaussianity at the end of inflation. This is because as soon as the non-attractor phase finishes, the amplitudes of super-horizon modes stop growing, and one recovers Maldacena's consistency relation. Thus, we claim that a robust prediction from canonical single field inflation (attractor or non-attractor) is that the observable squeezed limit of primordial non-Guassianity vanishes exactly.

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Primordial Black Holes from String Inflation

Cited by 22 publications

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Are primordial black holes produced by entropy perturbations in single field inflationary models?

Are primordial black holes produced by entropy perturbations in single field inflationary models?

Mechanisms for Primordial Black Hole Production in String Theory

Unifying attractor and non-attractor models of inflation under a single soft theorem

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