Cosmology without inflation

Peter, Patrick; Pinto-Neto, Nelson

doi:10.1103/physrevd.78.063506

Cited by 124 publications

(164 citation statements)

References 70 publications

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“…As far as the background is concerned, consider a contracting phase between t ini < 0 and t end < 0 dominated by a perfect fluid with constant equation of state parameter w, so that the scale factor behaves as a cont ∝ (−t) 2/[3(1+w)] ; we assume the bounce to take place at t = 0. The contribution of this contracting phase to the horizon is (we correct a misprint in [323] from which the argument is taken)…”

Section: Horizon Problemmentioning

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: Horizon Problemmentioning

confidence: 99%

A critical review of classical bouncing cosmologies

2015

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“…11, 13-15 can still be considered to be valid at the bounce. This should also be valid for other bouncing models, [7][8][9][10][11] as long as any bounce should take place at very short length scales, where the cosmological constant has no role.…”

Section: Introductionmentioning

confidence: 99%

“…If the contracting phase of a regular bouncing model is dominated by a perfect fluid, it has been shown by many authors, in different frameworks, [7][8][9][10][11][12] that this fluid must be dust, in order to reproduce a scale invariant spectrum of scalar and tensor cosmological perturbations.…”

Section: Introductionmentioning

confidence: 99%

“…Bouncing cosmological models, [1][2][3][4][5][6] which solve the singularity problem, can also be considered as possible alternatives to inflation, as long as they are able to solve the horizon and flatness problems, and justify the observed power spectrum of primordial cosmological perturbations.…”

Section: Introductionmentioning

confidence: 99%

“…where the H (1,2) ν are the Hankel functions of first and second kind, ν = 3w/2, and we have made a conformal time translation (η + η ∞ ) → η.…”

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confidence: 99%

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Bouncing Models With a Cosmological Constant

Pinto-Neto

Siffert

Maier

et al. 2011

Int. J. Mod. Phys. Conf. Ser.

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Most bouncing models contain a contracting phase from a very large and rarefied state, where dark energy might have had an important role. If this is that case, the presence of dark energy can modify the initial conditions and evolution of cosmological perturbations, changing the known results already obtained in the literature concerning their amplitude and spectrum. In this work, we assume the simplest and most appealing candidate for dark energy, the cosmological constant, and study its influence on the evolution of cosmological perturbations during the contracting phase of a bouncing model, containing also a perfect fluid with constant equation of state parameter w. We show that, due to the vacuum state choice we have to make when a cosmological constant is present, the spectrum of the perturbations are substantially altered. We conclude that, in this case, the presence of a stiff matter fluid in the contracting phase is needed in order to have a scale invariant spectrum of perturbations in the expanding phase.

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Black hole in asymmetric cosmological bounce

2021

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We determine the causal structure of the McVittie spacetime for a cosmological model with an asymmetric bounce. The analysis includes the computation of trapping horizons; regular, trapped, and antitrapped regions; and the integration of the trajectories of radial null geodesics before, during, and after the bounce. We find a trapped region since the beginning of the contracting phase up to shortly before the bounce, thus showing the existence of a black hole. When the universe reaches a certain minimum scale in the contracting phase, the trapping horizons disappear, and the central singularity becomes naked. These results suggest that neither a contracting nor an expanding universe can accommodate a black hole at all times.

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Cosmology without inflation

Cited by 124 publications

References 70 publications

A critical review of classical bouncing cosmologies

A critical review of classical bouncing cosmologies

Bouncing Models With a Cosmological Constant

Black hole in asymmetric cosmological bounce

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