Nonsingular big bounces and the evolution of linear fluctuations

Hwang, Jai‐chan; Noh, Hyerim

doi:10.1103/physrevd.65.124010

Cited by 95 publications

(160 citation statements)

References 63 publications

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“…Perhaps toy bouncing models using exotic scalar fields or matter in refs. [46,47] can be a good starting point to construct viable nonsingular Ekpyrotic models.…”

Section: Discussion and Open Issuesmentioning

confidence: 99%

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Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

2002

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We consider the construction of nonsingular Pre-Big-Bang and Ekpyrotic type cosmological models realized by the addition to the action of specific higher-order terms stemming from quantum corrections. We study models involving general relativity coupled to a single scalar field with a potential motivated by the Ekpyrotic scenario. We find that the inclusion of the string loop and quantum correction terms in the string frame makes it possible to obtain solutions of the variational equations which are nonsingular and bouncing in the Einstein frame, even when a negative exponential potential is present, as is the case in the Ekpyrotic scenario. This allows us to discuss the evolution of cosmological perturbations without the need to invoke matching conditions between two Einstein Universes, one representing the contracting branch, the second the expanding branch. We analyze the spectra of perturbations produced during the bouncing phase and find that the spectrum of curvature fluctuations in the model proposed originally to implement the Ekpyrotic scenario has a large blue tilt (nR = 3). Except for instabilities introduced on small scales, the result agrees with what is obtained by imposing continuity of the induced metric and of the extrinsic curvature across a constant scalar field (up to k 2 corrections equal to the constant energy density) matching surface between the contracting and the expanding Einstein Universes. We also discuss nonsingular cosmological solutions obtained when a Gauss-Bonnet term with a coefficient suitably dependent on the scalar matter field is added to the action in the Einstein frame with a potential for the scalar field present. In this scenario, nonsingular solutions are found which start in an asymptotically flat state, undergo a period of super-exponential inflation and end with a graceful exit. The spectrum of fluctuations is also calculated in this case.

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“…Perhaps toy bouncing models using exotic scalar fields or matter in refs. [46,47] can be a good starting point to construct viable nonsingular Ekpyrotic models.…”

Section: Discussion and Open Issuesmentioning

confidence: 99%

“…Thus, it is expected to lead to a successful graceful exit, in the same way that introducing matter violating the null energy condition allowed the construction of nonsingular bouncing models in [46,47].…”

Section: Inclusion Of Higher-order Corrections In the String Frammentioning

confidence: 99%

Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

2002

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“…The scalar perturbations can be read off from the formulation of Hwang & Noh (2002), which is independent of gauge. In the following we use units of M pl ≡ 1.…”

Section: Linear Perturbationsmentioning

confidence: 99%

Structure Formation in the Symmetron Model

Davis

Mota

et al. 2012

ApJ

108

142

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Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT Scalar fields, strongly coupled to matter, can be present in nature and still be invisible to local experiments if they are subject to a screening mechanism. The symmetron is one such mechanism that relies on restoration of a spontaneously broken symmetry in regions of high density to shield the scalar fifth force. We have investigated structure formation in the symmetron model by using N-body simulations and find observable signatures in both the linear and nonlinear matter power spectrum and on the halo mass function. The mechanism for suppressing the scalar fifth force in high-density regions is also found to work very well.

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“…Inflation models with multiple fields have been a fertile research topic for some time: see for example [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,60,49,50,51,52,53,54,55,56,57,58,59,60,61,62]. Some basic ingredients of the mechanism we describe here, such as the generation of isocurvature perturbations or non-flat metrics on field space, have been studied before in the context of slow-roll inflation.…”

Section: Introductionmentioning

confidence: 99%

Scale invariance in expanding and contracting universes from two-field models

Tolley

Wesley

2007

J. Cosmol. Astropart. Phys.

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We study cosmological perturbations produced by the most general twoderivative actions involving two scalar fields, coupled to Einstein gravity, with an arbitrary field space metric, that admit scaling solutions. For expanding universes, we find that scaleinvariant adiabatic perturbation spectra can be produced for any equation of state parameter w that satisfies −1 ≤ w < −1/3, and that all the scaling solutions are attractors. For contracting universes, we show that scale-invariant adiabatic perturbations can be produced continuously as modes leave the horizon for any w > −1/3. The corresponding background solutions are unstable, which we argue is a universal feature of contracting models that yield scale-invariant spectra. At no point do we assume slow-roll. The presence of a nontrivial metric on field space is a crucial ingredient in our results.

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Nonsingular big bounces and the evolution of linear fluctuations

Cited by 95 publications

References 63 publications

Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

Construction of nonsingular pre-big-bang and ekpyrotic cosmologies and the resulting density perturbations

Structure Formation in the Symmetron Model

Scale invariance in expanding and contracting universes from two-field models

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