Generating primordial black holes via hilltop-type inflation models

Alabidi, Laila; Kohri, Kazunori

doi:10.1103/physrevd.80.063511

Cited by 56 publications

(68 citation statements)

References 69 publications

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“…This is possible in models, such as the running mass model [22][23][24][25][26][27], where the power spectrum increases monotonically with increasing wave-number [6,7]. Another possibility is a peak in the primordial power spectrum, due to a phase transition during inflation or features in the inflation potential (see Ref.…”

Section: Primordial Black Hole Formation Constraintsmentioning

confidence: 99%

Primordial black holes as a tool for constraining non-Gaussianity

2012

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Primordial Black Holes (PBH's) can form in the early Universe from the collapse of large density fluctuations. Tight observational limits on their abundance constrain the amplitude of the primordial fluctuations on very small scales which can not otherwise be constrained, with PBH's only forming from the extremely rare large fluctuations. The number of PBH's formed is therefore sensitive to small changes in the shape of the tail of the fluctuation distribution, which itself depends on the amount of non-Gaussianity present. We study, for the first time, how quadratic and cubic local non-Gaussianity of arbitrary size (parameterised by fNL and gNL respectively) affects the PBH abundance and the resulting constraints on the amplitude of the fluctuations on very small scales. Intriguingly we find that even non-linearity parameters of order unity have a significant impact on the PBH abundance. The sign of the non-Gaussianity is particularly important, with the constraint on the allowed fluctuation amplitude tightening by an order of magnitude as fNL changes from just −0.5 to 0.5. We find that if PBH's are observed in the future, then regardless of the amplitude of the fluctuations, non-negligible negative fNL would be ruled out. Finally we show that gNL can have an even larger effect on the number of PBH's formed than fNL.PACS numbers: 95.35.+d

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Section: Primordial Black Hole Formation Constraintsmentioning

confidence: 99%

Primordial black holes as a tool for constraining non-Gaussianity

2012

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“…[4,5], we investigated this case, and argued there that the relative large amplitude of the potential Ψ can be achieved on subhorizon scales and may lead to the overproduction of PBHs at the end of inflation. The constraint on the amplitude of the curvature perturbation is then tighter than the current bound from the PBHs formed throughout the radiation epoch [5] (for the constraints on the "standard" formation of PBHs see [6][7][8][9][10][11][12][13][14][15][16]). …”

Section: Introductionmentioning

confidence: 99%

Boosted perturbations at the end of inflation

Zaballa

Sasaki²

2010

J. Cosmol. Astropart. Phys.

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We study the effect on the primordial cosmological perturbations of a sharp transition from inflationary to a radiation and matter dominated epoch respectively. We assume that the perturbations are generated by the vacuum fluctuations of a scalar field slowly rolling down its potential, and that the transition into the subsequent epoch takes place much faster than a Hubble time. The behaviour of the superhorizon perturbations corresponding to cosmological scales in this case is well known. However, it is not clear how perturbations on scales of and smaller than the Hubble horizon scale at the end of inflation may evolve through such a transition. We derive the evolution equation for the gravitational potential Ψ, which allows us to study the evolution of the perturbations on all scales under these circumstances. We show that for a certain range of scales inside the horizon at the end of inflation, the amplitude of the perturbations are enhanced relative to the superhorizon scales. This enhancement may lead to the overproduction of Primordial Black Holes (PBHs), and therefore constrain the dynamics of the transitions that take place at the end of inflation.

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“…On the other hand, the additional parameters (n sk , n skk ) do not only help to describe the underlying model more accurately on observable scales, but they also allow for additional shapes of the potential at stages of inflation away from the observable range. In general, we want to avoid positive values of the running as they may result in an over-production of Primordial Black Holes (PBHs) at the smallest scales, near the end of inflation [16,17]. We will address this point for the case of HNI in Sec.…”

Section: Slow-roll Parameterisation Of Spectramentioning

confidence: 99%

“…Such truncated expansions may seem incomplete to evaluate the amplitude of the spectrum, at about 50 e-folds away from observable scales, but they have been successfully employed to constrain undetermined parameters (e.g. [28,16,17]). Our equation (20) is only a first approximation to establish a bound on the undetermined value of the running n sk and therefore to constrain the predictions of HNI.…”

Section: Consistency Checks: F ≤ 1 and Bounds On Primordial Black Holmentioning

confidence: 99%

“…We do this for three different cases: The general HNI model with no priors on the pair of parameters {a, f }, the case a = 1 corresponding to WNI, and finally the case with no prior over a but with the symmetry breaking scale f restricted to the largest physical value f = 1, in Planck units. In Section 4 we analyse the featured results identifying pathological cases where either the scale f acquires unphysically large values, or where the running could over-produce primordial black holes, as is the case for other models of inflation where the potential slope flattens toward the end of inflation [16,17]. Finally, in Section 5 we conclude by discussing the observational and theoretical constraints to the featured models.…”

Section: Introductionmentioning

confidence: 99%

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Constraining hybrid natural inflation with recent CMB data

Vázquez

González

Germán

et al. 2015

J. Cosmol. Astropart. Phys.

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We study the Hybrid Natural Inflation (HNI) model and some of its realisations in the light of recent CMB observations, mainly Planck temperature and WMAP-9 polarization, and compare with the recent release of BICEP2 dataset. The inflationary sector of HNI is essentially given by the potential, where a is a positive constant smaller or equal to one and f is the scale of (pseudo Nambu-Goldstone) symmetry breaking. We show that to describe the HNI model realisations we only need two observables; the spectral index n s , the tensor-to-scalar ratio, and a free parameter in the amplitude of the cosine function a. We find that in order to make the HNI model compatible with the BICEP2 observations, we require a large positive running of the spectra. We find that this could over-produce primordial black holes (PBHs) in the most theoretically consistent case of the model. This situation could be alleviated if, as recently argued, the BICEP2 data do not correspond to primordial gravitational waves.

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Generating primordial black holes via hilltop-type inflation models

Cited by 56 publications

References 69 publications

Primordial black holes as a tool for constraining non-Gaussianity

Primordial black holes as a tool for constraining non-Gaussianity

Boosted perturbations at the end of inflation

Constraining hybrid natural inflation with recent CMB data

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