Cosmology of the Very Early Universe

Brandenberger, Robert H.; Dupke, Renato A.; Alcaniz, J. S.; Reza, R. de la; Daflon, S.

doi:10.1063/1.3483879

Cited by 82 publications

(84 citation statements)

References 196 publications

(391 reference statements)

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“…In fact, the growth rate is precisely the correct one to convert an initial vacuum spectrum into a scale-invariant one (see e.g. [9] for a review).…”

Section: A Fluctuations In the Matter Bouncementioning

confidence: 99%

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Evolution of cosmological perturbations and the production of non-Gaussianities through a nonsingular bounce: Indications for a no-go theorem in single field matter bounce cosmologies

et al. 2015

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Assuming that curvature perturbations and gravitational waves originally arise from vacuum fluctuations in a matter-dominated phase of contraction, we study the dynamics of the cosmological perturbations evolving through a nonsingular bouncing phase described by a generic single scalar field Lagrangian minimally coupled to Einstein gravity. In order for such a model to be consistent with the current upper limits on the tensor-to-scalar ratio, there must be an enhancement of the curvature fluctuations during the bounce phase. We show that, while it remains possible to enlarge the amplitude of curvature perturbations due to the nontrivial background evolution, this growth is very limited because of the conservation of curvature perturbations on super-Hubble scales. We further perform a general analysis of the evolution of primordial non-Gaussianities through the bounce phase. By studying the general form of the bispectrum we show that the non-Gaussianity parameter fNL (which is of order unity before the bounce phase) is enhanced during the bounce phase if the curvature fluctuations grow. Hence, in such nonsingular bounce models with matter given by a single scalar field, there appears to be a tension between obtaining a small enough tensor-to-scalar ratio and not obtaining a value of fNL in excess of the current upper bounds. This conclusion may be considered as a "no-go" theorem that rules out any single field matter bounce cosmology starting with vacuum initial conditions for the fluctuations.1 Such a negative potential may arise from the standard model Higgs field since, based on the recent Higgs and top quark mass measurements, the standard model Higgs develops an instability at large field values (in the absence of new physics) [26].

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“…In fact, the growth rate is precisely the correct one to convert an initial vacuum spectrum into a scale-invariant one (see e.g. [9] for a review).…”

Section: A Fluctuations In the Matter Bouncementioning

confidence: 99%

“…This scenario of structure formation alternative to inflation is called the "matter bounce" scenario (see e.g. [8,9] for reviews).…”

mentioning

confidence: 99%

Evolution of cosmological perturbations and the production of non-Gaussianities through a nonsingular bounce: Indications for a no-go theorem in single field matter bounce cosmologies

et al. 2015

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“…It is true that cosmological inflation is the first model where such a spectrum emerges from first principles, but it is not the only one (see e.g. [20] for a recent review of alternatives).…”

Section: Arxiv:150502381v1 [Hep-th] 10 May 2015mentioning

confidence: 99%

String gas cosmology after Planck

Brandenberger

2015

Class. Quantum Grav.

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We review the status of String Gas Cosmology after the 2015 Planck data release. String gas cosmology predicts an almost scale-invariant spectrum of cosmological perturbations with a slight red tilt, like the simplest inflationary models. It also predicts a scale-invariant spectrum of gravitational waves with a slight blue tilt, unlike inflationary models which predict a red tilt of the gravitational wave spectrum. String gas cosmology yields two consistency relations which determine the tensor to scalar ratio and the slope of the gravitational wave spectrum given the amplitude and tilt of the scalar spectrum. We show that these consistency relations are in good agreement with the Planck data. We discuss future observations which will be able to differentiate between the predictions of inflation and those of string gas cosmology. ‡ However, beyond linear order the story may be very different [8,9,10]. Also, in the case of small field inflation there is an initial condition problem [11].

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“…As proposed recently in Ref. [2], observational cosmology is so thriving that its data might help understand particle physics beyond the Standard Model and the reach of present or future particle accelerators, thus 'probing particle physics from top down'. An example of such cosmological objects is the concept of cosmic strings, which may occur in some quantum field theories in the form of linear defects in stable field configurations [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Non-commutativity and non-inertial effects on the Dirac oscillator in a cosmic string space–time

2019

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We examine the non-inertial effects of a rotating frame on a Dirac oscillator in a cosmic string space-time with non-commutative geometry in phase space. We observe that the approximate bound-state solutions are related to the biconfluent Heun polynomials. The related energies cannot be obtained in a closed form for all the bound states. We find the energy of the fundamental state analytically by taking into account the hard-wall confining condition. We describe how the ground-state energy scales with the new non-commutative term as well as with the other physical parameters of the system.

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Cosmology of the Very Early Universe

Cited by 82 publications

References 196 publications

Evolution of cosmological perturbations and the production of non-Gaussianities through a nonsingular bounce: Indications for a no-go theorem in single field matter bounce cosmologies

Evolution of cosmological perturbations and the production of non-Gaussianities through a nonsingular bounce: Indications for a no-go theorem in single field matter bounce cosmologies

String gas cosmology after Planck

Non-commutativity and non-inertial effects on the Dirac oscillator in a cosmic string space–time

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