Effects of the speed of sound at large<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi></mml:math>

Zavala, Ivonne

doi:10.1103/physrevd.91.063005

Cited by 8 publications

(8 citation statements)

References 28 publications

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“…possibly up to higher-order corrections in 1/N , where N is the number of e-folds between horizon crossing of the CMB modes and the end of inflation. Interestingly, this relation generically allows for only two regimes of the tensor-to-scalar ratio r, which is either given by r = 8/N or scales as 1/N 2 at lowest order [4,5] (see also [6][7][8]). Furthermore, assuming eq.…”

Section: Introductionmentioning

confidence: 99%

Cosmological attractors fromα-scale supergravity

2015

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The Planck value of the spectral index can be interpreted as ns = 1 − 2/N in terms of the number of e-foldings N . An appealing explanation for this phenomenological observation is provided by α-attractors: the inflationary predictions of these supergravity models are fully determined by the curvature of the Kähler manifold. We provide a novel formulation of α-attractors which only involves a single chiral superfield. Our construction involves a natural deformation of no-scale models, and employs these to construct a De Sitter plateau with an exponential fall-off. Finally, we show how analogous structures with a flat Kähler geometry arise as a singular limit of such α-scale models.

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Section: Introductionmentioning

confidence: 99%

Cosmological attractors fromα-scale supergravity

2015

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“…An example is a quadratic potential, V (φ) = m 2 φ 2 , which produces tensor/scalar ratio r ∼ 0.15, and is therefore ruled out by Planck/BICEP/Keck [20]. (Previous work [21][22][23][24] has considered the effect of a lower bound on r on the speed of sound inflationary model building. In this paper, we consider the effect of an upper bound, consistent with current constraints.…”

Section: Introductionmentioning

confidence: 99%

Planck limits on non-canonical generalizations of large-field inflation models

Stein¹,

Kinney

2017

J. Cosmol. Astropart. Phys.

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In this paper, we consider two case examples of Dirac-Born-Infeld (DBI) generalizations of canonical large-field inflation models, characterized by a reduced sound speed, c S < 1. The reduced speed of sound lowers the tensor-scalar ratio, improving the fit of the models to the data, but increases the equilateral-mode non-Gaussianity, f equil. NL , which the latest results from the Planck satellite constrain by a new upper bound. We examine constraints on these models in light of the most recent Planck and BICEP/Keck results, and find that they have a greatly decreased window of viability. The upper bound on f equil. NL corresponds to a lower bound on the sound speed and a corresponding lower bound on the tensor-scalar ratio of r ∼ 0.01, so that near-future Cosmic Microwave Background observations may be capable of ruling out entire classes of DBI inflation models. The result is, however, not universal: infrared-type DBI inflation models, where the speed of sound increases with time, are not subject to the bound. arXiv:1609.08959v3 [astro-ph.CO]

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“…The implications of a smaller than unity speed of sound for the cosmological observables (n s , r, α s ) in a model independent large-N approach was studied in[86], while frameworks to study large deviations from a slow-roll regime in similar contexts were developed in[87][88][89].…”

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confidence: 99%

Mechanisms for primordial black hole production in string theory

Özsoy

Parameswaran

Tasinato

et al. 2018

J. Cosmol. Astropart. Phys.

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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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Effects of the speed of sound at largeN

Cited by 8 publications

References 28 publications

Cosmological attractors fromα-scale supergravity

Cosmological attractors fromα-scale supergravity

Planck limits on non-canonical generalizations of large-field inflation models

Mechanisms for primordial black hole production in string theory

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