Vector perturbations in a contracting Universe

Battefeld, Thorsten; Brandenberger, Robert H.

doi:10.1103/physrevd.70.121302

Cited by 50 publications

(92 citation statements)

References 29 publications

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“…However, if we start with a universe initially devoid of vector perturbations and only scalars are present, this hurdle can be overcome as scalars do not source vector perturbations [245]. This is possible as vector perturbations, not being dynamical in this context, do not need to have non-vanishing initial conditions coming from, e.g.…”

Section: B Growth Of Quantum Induced Anisotropymentioning

confidence: 99%

“…This work superseded that of [170] which set up the building blocks to obtain scale-invariant entropy perturbations within the ekpyrotic scenario via non-minimally coupled massless scalar fields. There, it was suggested that the entropy perturbation could be converted into curvature perturbations by means of a curvaton, as done in [169], or modulated (p)reheating [245]. Non-Gaussianities for the model in [169] where computed in [171], see the non-minimal entropic mechanism in Table II.…”

Section: F Nonsingular Bounces Via a Galileonmentioning

confidence: 99%

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A critical review of classical bouncing cosmologies

2015

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Given the proliferation of bouncing models in recent years, we gather and critically assess these proposals in a comprehensive review. The PLANCK data shows an unmistakably red, quasi scaleinvariant, purely adiabatic primordial power spectrum and no primary non-Gaussianities. While these observations are consistent with inflationary predictions, bouncing cosmologies aspire to provide an alternative framework to explain them. Such models face many problems, both of the purely theoretical kind, such as the necessity of violating the NEC and instabilities, and at the cosmological application level, as exemplified by the possible presence of shear. We provide a pedagogical introduction to these problems and also assess the fitness of different proposals with respect to the data. For example, many models predict a slightly blue spectrum and must be fine-tuned to generate a red spectral index; as a side effect, large non-Gaussianities often result.We highlight several promising attempts to violate the NEC without introducing dangerous instabilities at the classical and/or quantum level. If primordial gravitational waves are observed, certain bouncing cosmologies, such as the cyclic scenario, are in trouble, while others remain valid. We conclude that, while most bouncing cosmologies are far from providing an alternative to the inflationary paradigm, a handful of interesting proposals have surfaced, which warrant further research. The constraints and lessons learned as laid out in this review might guide future research.

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Section: B Growth Of Quantum Induced Anisotropymentioning

confidence: 99%

Section: F Nonsingular Bounces Via a Galileonmentioning

confidence: 99%

A critical review of classical bouncing cosmologies

2015

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“…Note that vector and tensor perturbations are important (see e.g. [47]) in topological defects models of structure formation and in bouncing cosmologies [48].…”

Section: Classifying Fluctuationsmentioning

confidence: 99%

Cosmology of the Very Early Universe

Brandenberger

Dupke²,

Alcaniz³

et al. 2010

AIP Conference Proceedings

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In these lectures I focus on early universe models which can explain the currently observed structure on large scales. I begin with a survey of inflationary cosmology, the current paradigm for understanding the origin of the universe as we observe it today. I will discuss some progress and problems in inflationary cosmology before moving on to a description of two alternative scenariosthe Matter Bounce and String Gas Cosmology. All early universe models connect to observations via the evolution of cosmological perturbations -a topic which will be discussed in detail in these lectures.

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“…Vector perturbations (VP) have recently been studied in the context of bouncing cosmologies, due to their growing nature in a contracting Universe [44,45]. However, if the fluid is stiff enough, VP will also grow in an expanding Universe (as was first pointed out in [46]).…”

Section: Vector Perturbations In Thementioning

confidence: 99%

“…If we assume for simplicity π i = 0 (no anisotropic stress), the equations of motion for each Fourier mode V k and S k are solved by [44] …”

Section: Vector Perturbations In Thementioning

confidence: 99%

Perturbations in a holographic universe and in other stiff fluid cosmologies

Battefeld

Easson

2004

Phys. Rev. D

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We examine the generation and evolution of perturbations in a universe dominated by a fluid with stiff equation of state p = ρ. The recently proposed Holographic Universe is an example of such a model. We compute the spectrum of scalar and tensor perturbations, without relying on a microphysical description of the p = ρ fluid. The spectrum is scale invariant deep inside the Hubble horizon. In contrast, infrared perturbations that enter the Hubble horizon during the stiff fluid dominated (holographic) phase yield oscillatory and logarithmic terms in the power spectrum. We show that vector perturbations grow during the stiff fluid dominated epoch and may result in a turbulent and anisotropic Universe at the end of the holographic phase. Therefore, the required period of inflation following the holographic phase cannot be much shorter than that required in standard inflationary models.PACS numbers: 98.80.Cq.

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Vector perturbations in a contracting Universe

Cited by 50 publications

References 29 publications

A critical review of classical bouncing cosmologies

A critical review of classical bouncing cosmologies

Cosmology of the Very Early Universe

Perturbations in a holographic universe and in other stiff fluid cosmologies

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