Two field matter bounce cosmology

Cai, Yi-Fu; McDonough, Evan; Duplessis, Francis; Brandenberger, Robert H.

doi:10.1088/1475-7516/2013/10/024

Cited by 143 publications

(173 citation statements)

References 71 publications

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“…This can also be seen from the expression (22), owing to the fact that a Big Rip requiresḢ > 0, and we discussed this issue previously, below Eq. (14). But we can explicitly show that indeed a phantom dark energy era occurs at very late times, since a direct calculation yields that, as t → t s , and during the dark energy era, the EoS becomes approximately equal to,…”

Section: Figmentioning

confidence: 77%

Deformed matter bounce with dark energy epoch

Odintsov

Oikonomou

2016

Phys. Rev. D

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We extend the Loop Quantum Cosmology matter bounce scenario in order to include a dark energy era, which ends abruptly at a Rip singularity where the scale factor and the Hubble rate diverge. In the "deformed matter bounce scenario", the Universe is contracting from an initial non-causal matter dominated era until it reaches a minimal radius. After that it expands in a decelerating way, until at late times, where it expands in an accelerating way, thus the model is described by a dark energy era that follows the matter dominated era. Depending on the choice of the free parameters of the model, the dark energy era is quintessential like which follows the matter domination era, and eventually it crosses the phantom divide line and becomes phantom. At the end of the dark energy era, a Rip singularity exists, where the scale factor and Hubble rate diverge, however the physical system cannot reach the singularity, since the effective energy density and pressure become complex. This indicates two things, firstly that the ordinary Loop Quantum Cosmology matter bounce evolution stops, thus ending the infinite repetition of the ordinary matter bounce scenario. Secondly, the fact that both the pressure and the density become complex indicates probably that the description of the cosmic evolution within the theoretical context of Loop Quantum Cosmology, ceases to describe the physics of the system and possibly a more fundamental theory of quantum gravity is needed near the would be Rip singularity. We describe the qualitative features of the model and we also investigate how this cosmology could be realized by a viscous fluid in the context of Loop Quantum Cosmology. In addition to this, we show how this deformed model can be realized by a canonical scalar field filled Universe, in the context of Loop Quantum Cosmology. Finally, we demonstrate how the model can be generated by a vacuum F (R) gravity.

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Section: Figmentioning

confidence: 77%

Deformed matter bounce with dark energy epoch

Odintsov

Oikonomou

2016

Phys. Rev. D

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“…So we write the modified Friedmann equations (57) and (58) in the case of unimodular f (T ) gravity as…”

Section: Physics Of Torsion Fluidmentioning

confidence: 99%

Lorenz gauge fixing of f(T) teleparallel cosmology

Hanafy

Nashed

2017

Int. J. Mod. Phys. D

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In teleparallel gravity, we apply Lorenz type gauge fixing to cope with redundant degrees of freedom in the vierbein field. This condition is mainly to restore the Lorentz symmetry of the teleparallel torsion scalar. In cosmological application, this technique provides standard cosmology, turnaround, bounce or ΛCDM as separate scenarios. We reconstruct the f (T ) gravity which generates these models. We study the stability of the solutions by analyzing the corresponding phase portraits. Also, we investigate Lorenz gauge in the unimodular coordinates, it leads to unify a nonsingular bounce and standard model cosmology in a single model, where crossing the phantom divide line is achievable through a finite-time singularity of Type IV associated with a de Sitter fixed point. We reconstruct the unimodular f (T ) gravity which generates the unified cosmic evolution showing the role of the torsion gravity to establish a healthy bounce scenario.PACS numbers: 98.80.Qc, 04.20.Cv, 98.80.Cq.

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“…In these models, one ought to be aware of the potential graceful exit problem as well as the gradient instability issue. For example, in a concrete cosmology of two-field matter bounce [92], it was found that the model can be free from these dangerous issues with cosmological perturbations evolving through the nonsingular bouncing phase almost unchanged [93]. Accordingly, the tensor-to-scalar ratio could be too large to explain the CMB observations and may require a curvaton mechanism [23] to give rise to an enhancement on curvature perturbations from entropy fluctuations.…”

Section: Problems With Particular Bounce Modelsmentioning

confidence: 99%

An extended matter bounce scenario: current status and challenges

Haro

Cai

2015

Gen Relativ Gravit

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As an alternative to the paradigm of slow roll inflation, we propose an extended scenario of the matter bounce cosmology in which the Universe has experienced a quasi-matter contracting phase with a variable background equation of state parameter. This extended matter bounce scenario can be realized by considering a single scalar field evolving along an approximately exponential potential. Our result reveals that the rolling of the scalar field in general leads to a running behavior on the spectral index of primordial cosmological perturbations and a negative running can be realized in this model. We constrain the corresponding parameter space by using the newly released Planck data. To apply this scenario, we revisit bouncing cosmologies within the context of modified gravity theories, in particular, the holonomy corrected loop quantum cosmology and teleparallel F (T ) gravity. A gravitational process of reheating is presented in such a matter bounce scenario to demonstrate the condition of satisfying current observations. We also comment on several unresolved issues that often appear in matter bounce models.

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Two field matter bounce cosmology

Cited by 143 publications

References 71 publications

Deformed matter bounce with dark energy epoch

Deformed matter bounce with dark energy epoch

Lorenz gauge fixing of f(T) teleparallel cosmology

An extended matter bounce scenario: current status and challenges

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