Cyclic Magnetic Universe

Novello, M.; Araújo, Ana Lucélia de; Salim, J. M.

doi:10.1142/s0217751x09046321

Cited by 18 publications

(18 citation statements)

References 18 publications

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“…Other studies pertaining to the cylic universe, which are not reviewed here, include: 5D dynamics of general braneworld models [174], past-shrinking cycles that spend more time in an entropy conserving Hagedorn phase [175], a cyclic magnetic universe [176,177], phantom accretion onto black holes [178], deformed Hořava-Lifshitz gravity [179], a string-inspired model via a scalartachyon coupling and a contribution from curvature in a closed universe [180], cosmological hysteresis [181], Finsler-like gravity theories constructed on tangent bundles to Lorentz manifolds [182], a combination of cyclic and inflationary phases with quintessence [183] and a cyclic model with a chameleon field [184], among others [185][186][187].…”

Section: B Ekpyrotic and Cyclic Scenariosmentioning

confidence: 99%

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 Ekpyrotic and Cyclic Scenariosmentioning

confidence: 99%

A critical review of classical bouncing cosmologies

2015

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“…The first situation is realised in the pre-big-bang (PBB) scenario [23,24]; it requires a long accelerated phase originating from either an asymptotically zero volume flat spacetime or from a finite but small compact region [25,26] before the usual decelerated expansion of the standard model. As for bouncing models, they can be embedded in many theoretical situations [27,28,29,30,31,32,33,34,35,36,37,38,39], including classically singular cases [40,41,42]. In a string approach, both situations are in practice equivalent due to the presence of the dilaton which allows for a field reparametrization (as opposed to conformal transformation as is usually, and erroneously, stated): the PBB evolution of the Jordan (or string) frame is turned to a bounce in the Einstein frame.…”

Section: Introductionmentioning

confidence: 99%

Cosmology without inflation

2008

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We propose a new cosmological paradigm in which our observed expanding phase is originated from an initially large contracting Universe that subsequently experienced a bounce. This category of models, being geodesically complete, is non-singular and horizon-free, and can be made to prevent any relevant scale to ever have been smaller than the Planck length. In this scenario, one can find new ways to solve the standard cosmological puzzles. One can also obtain scale invariant spectra for both scalar and tensor perturbations: this will be the case, for instance, if the contracting Universe is dust-dominated at the time at which large wavelength perturbations get larger than the curvature scale. We present a particular example based on a dust fluid classically contracting model, where a bounce occurs due to quantum effects, in which these features are explicit.

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“…Over the last few years there has been a significant amount of interest in cosmological models involving nonlinear electromagnetic fields [1,2,3]. If the early universe is dominated by radiation governed by Maxwell's equations it is well known that there will be a spacelike initial singularity in the past.…”

Section: Introductionmentioning

confidence: 99%

“…At late times the µ/F 2 term dominates and the universe enters an accelerated expansion phase. It has also been shown [2] that if a term proportional to 1/F 4 is added to the Lagrangian the expansion will eventually end and the universe will begin to collapse, until it bounces again. Thus, this model produces a cyclic magnetic universe.…”

Section: Introductionmentioning

confidence: 99%

Homogeneous and isotropic cosmologies with nonlinear electromagnetic radiation

Vollick

2008

Phys. Rev. D

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In this paper I examine cosmological models that contain a stochastic background of nonlinear electromagnetic radiation. I show that for Born-Infeld electrodynamics the equation of state parameter, w = P/ρ, remains close to 1/3 throughout the evolution of the universe if E 2 = B 2 in the late universe to a high degree of accuracy.Theories with electromagnetic Lagrangians of the form L = − 1 4 F 2 +αF 4 have recently been studied in magnetic universes, where the electric field vanishes. It was shown that the F 4 term can produce a bounce in the early universe, avoiding an initial singularity. Here I show that the inclusion of an electric field, with E 2 ≃ B 2 in the late universe, eliminates the bounce and the universe "begins" in an initial singularity.I also examine theories with Lagrangians of the form L = − 1 4 F 2 − µ 8 /F 2 , which have been shown to produce a period of late time accelerated expansion in magnetic universes. I show that, if an electric field is introduced, the accelerated phase will only occur if E 2 < 3B 2 .

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Cyclic Magnetic Universe

Cited by 18 publications

References 18 publications

A critical review of classical bouncing cosmologies

A critical review of classical bouncing cosmologies

Cosmology without inflation

Homogeneous and isotropic cosmologies with nonlinear electromagnetic radiation

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