Kasner and mixmaster behavior in universes with equation of state<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>w</mml:mi><mml:mo>&gt;~</mml:mo><mml:mn>1</mml:mn></mml:math>

Erickson, Joel K.; Wesley, Daniel H.; Steinhardt, Paul J.; Turok, Neil

doi:10.1103/physrevd.69.063514

Cited by 262 publications

(342 citation statements)

References 28 publications

(55 reference statements)

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“…Contrary to Lemaître's model, the cyclic universe has an added component, a phase of ekpyrotic contraction [335,336], that bounded. In [151], Lehners et al envisioned reheating in the cylic scenario as occurring via the transfer of some kinetic energy between branes.…”

Section: Avoidance Of Relicsmentioning

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: Avoidance Of Relicsmentioning

confidence: 99%

“…Thus, distortions and anisotropies are expected to be strongly amplified during contraction in cyclic or ekpyrotic cosmologies. However, prior analytic [335] and numerical studies [336] …”

Section: Bkl Instabilitymentioning

confidence: 99%

A critical review of classical bouncing cosmologies

2015

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“…Nevertheless, such possibilities have been seriously considered [93], and we do not rule them out completely, at least not in the very early Universe. In short, it is possible to keep the brane action positive everywhere, but only by means of choosing rather extreme parameter values.…”

Section: Brane Pair Production: Constant Eos Parametermentioning

confidence: 99%

The phantom divide in string gas cosmology

McInnes

2005

Nuclear Physics B

102

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One of the main virtues of string gas cosmology is that it resolves cosmological singularities. Since the Universe can be approximated by a locally asymptotically de Sitter spacetime by the end of the inflationary era, a singularity theorem implies that these cosmologies effectively violate the Null Energy Condition [not just the Strong Energy Condition]. We stress that this is an extremely robust result, which does not depend on assuming that the spatial sections remain precisely flat in the early Universe. This means, however, that it must be possible for string cosmologies to cross the recently much-discussed phantom divide [from w < −1 to w > −1, where w is the equation-ofstate parameter]. This naturally raises the question as to whether the phantom divide can be crossed again, to account for recent observations suggesting that w < −1 at the present time. We argue that non-perturbative string effects rule out this possibility, even if the NEC violation in question is only "effective".

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“…Other aspects of the cyclic and ekpyrotic models have been criticized [11] (see [12] for replies), and some have argued that a bounce is impossible altogether [13]. While the consistency of a bounce remains to be proven, recent work has shown that the traditional hazard of chaotic mixmaster behavior is strongly suppressed in the contracting phase of the cyclic model [14]. The metric perturbations exhibit ultralocal behavior in which anisotropies remain small, right up to a few Planck times before the bounce.…”

Section: Introductionmentioning

confidence: 99%

New duality relating density perturbations in expanding and contracting Friedmann cosmologies

Boyle

Steinhardt

Turok³

2004

Phys. Rev. D

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For a 4-dimensional spatially-flat Friedmann-Robertson-Walker universe with a scalar field φ(x), potential V (φ) and constant equation of state w = p/ρ, we show that an expanding solution characterized by ǫ = 3(1 + w)/2 produces the same scalar perturbations as a contracting solution with ǫ = 1/ǫ. The same symmetry applies to both the dominant and subdominant scalar perturbation modes. This result admits a simple physical interpretation and generalizes to d spacetime dimensions if we define ǫ ≡ [(2d − 5) + (d − 1)w]/(d − 2).

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Kasner and mixmaster behavior in universes with equation of statew>~1

Cited by 262 publications

References 28 publications

A critical review of classical bouncing cosmologies

A critical review of classical bouncing cosmologies

The phantom divide in string gas cosmology

New duality relating density perturbations in expanding and contracting Friedmann cosmologies

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