Fermi-bounce cosmology and scale-invariant power spectrum

Alexander, Stephon; Bambi, Cosimo; Marcianò, Antonino; Modesto, Leonardo

doi:10.1103/physrevd.90.123510

Cited by 30 publications

(41 citation statements)

References 66 publications

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“…Note that there is another equation of motion to describe the dynamics of cosmological perturbations, namely the perturbed equation for δφ. However, it can be shown that this equation is consistent with (421) and (424) by applying (422).…”

Section: Perturbation Analysissupporting

confidence: 65%

“…Accompanied with this feature, it is not surprising to look for a series of nontrivial cosmological solutions that may resolve the initial singularity problem [419]. The avoidance of the Big Bang singularity by using torsion arisen from a cosmic spinor field can be found in [420][421][422][423]. Moreover, it has been known for many years that the coupling between the torsion tensor and the cosmic spinor field can lead to interesting gravitational repulsion and thus avoid curvature singularities by violating the energy condition [424][425][426][427][428][429][430].…”

Section: Cosmic Bouncementioning

confidence: 99%

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f(T) teleparallel gravity and cosmology

et al. 2016

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Over the past decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T ) gravity, where f (T ) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T ) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T ) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T ) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations, or alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T ) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T ) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to enlighten the subject of which formulation, or combination of formulations, might be more suitable for quantization ventures and cosmological applications. Contents

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Section: Perturbation Analysissupporting

confidence: 65%

Section: Cosmic Bouncementioning

confidence: 99%

f(T) teleparallel gravity and cosmology

et al. 2016

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“…This raises serious questions regarding stability and the fate of perturbations. A similar model, in which a topological sector is added to gravity, was proposed in which the bounce behaves in a more regular way; by adjusting the fermion number density and the mass, such a model can reproduce a scaleinvariant spectrum of perturbations [320].…”

Section: Spinors and Torsionmentioning

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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“…We require a bounce mechanism (see e.g. [21][22][23][24][25]) only to transition from contraction to expansion, the modes that we are observing today at CMB exits prior to the bounce. Our scenario is also very distinct from the ekpyrotic case [26] which operates at w 1 whereas we have w ≈ 1.…”

Section: Jhep08(2014)116mentioning

confidence: 99%

Atick-Witten Hagedorn conjecture, near scale-invariant matter and blue-tilted gravity power spectrum

Biswas

Koivisto

Mazumdar

2014

J. High Energ. Phys.

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We will provide an interesting new mechanism to generate almost scale invariant seed density perturbations with a red spectrum, while keeping the gravitational wave spectrum blue-tilted in a stringy thermal contracting phase at temperatures beyond the Hagedorn temperature. This phase is often referred to as the Hagedorn phase where the free energy has been conjectured by Atick and Witten to grow more slowly than ordinary radiation. The primordial fluctuations are created by the statistical thermal fluctuations determined by the partition function, rather than quantum vacuum driven fluid dynamical fluctuations. Our mechanism assumes a non-singular bounce.

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Fermi-bounce cosmology and scale-invariant power spectrum

Cited by 30 publications

References 66 publications

f(T) teleparallel gravity and cosmology

f(T) teleparallel gravity and cosmology

A critical review of classical bouncing cosmologies

Atick-Witten Hagedorn conjecture, near scale-invariant matter and blue-tilted gravity power spectrum

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