Inflationary Cosmology in Modified Gravity Theories

Bamba, Kazuharu; Odintsov, Sergei D.

doi:10.3390/sym7010220

Cited by 341 publications

(202 citation statements)

References 171 publications

(234 reference statements)

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“…This nicely extends the universe evolution picture, taking into account that early universe was also eventually accelerating (early-time inflation [4]). The early-time inflation maybe also described in terms of F (R) gravity (for recent review, see [5]). The most appealing models of modified gravity pass most of the tests posed by observations and by local gravity constraints, and also offer the possibility for a unified description of early-time and late-time acceleration, within the same theoretical framework [2,6].…”

Section: Introductionmentioning

confidence: 99%

Accelerating cosmologies and the phase structure ofF(R)gravity with Lagrange multiplier constraints: A mimetic approach

Odintsov

Oikonomou

2016

Phys. Rev. D

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We study mimetic F (R) gravity with potential and Lagrange multiplier constraint. In the context of these theories, we introduce a reconstruction technique which enables us to realize arbitrary cosmologies, given the Hubble rate and an arbitrarily chosen F (R) gravity. We exemplify our method by realizing cosmologies that are in concordance with current observations (Planck data) and also well known bouncing cosmologies. The attribute of our method is that the F (R) gravity can be arbitrarily chosen, so we can have the appealing features of the mimetic approach combined with the known features of some F (R) gravities, which unify early-time with late-time acceleration. Moreover, we study the existence and the stability of de Sitter points in the context of mimetic F (R) gravity. In the case of unstable de Sitter points, it is demonstrated that graceful exit from inflation occurs. We also study the Einstein frame counterpart theory of the Jordan frame mimetic F (R) gravity, we discuss the general properties of the theory and exemplify our analysis by studying a quite interesting from a phenomenological point of view, model with two scalar fields. We also calculate the observational indices of the two scalar field model, by using the two scalar field formalism. Furthermore, we extensively study the dynamical system that corresponds to the mimetic F (R) gravity, by finding the fixed points and studying their stability. Finally, we modify our reconstruction method to function in the inverse way and thus yielding which F (R) gravity can realize a specific cosmological evolution, given the mimetic potential and the Lagrange multiplier.PACS numbers: 95.35.+d, 98.80.Cq, 95.36.+x

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Section: Introductionmentioning

confidence: 99%

Accelerating cosmologies and the phase structure ofF(R)gravity with Lagrange multiplier constraints: A mimetic approach

Odintsov

Oikonomou

2016

Phys. Rev. D

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“…The inflationary paradigm for early-time cosmology is a consistent framework, in which many theoretical inconsistencies of the Big Bang cosmology were appropriately addressed [1][2][3][4][5]. However, inflation theories suffer from the initial singularity problem [6] at the origin t = 0, and this initial singularity is a crushing type timelike singularity [7], which means that the spacetime is geodesically incomplete at that time instance.…”

Section: Introductionmentioning

confidence: 99%

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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“…As a simple generalization of the R 2 inflation, many people (Martin et al 2014a,b,c;Codello et al 2014;Rinaldi et al 2014c,b,c;Motohashi 2014;Myrzakul et al 2015;Nojiri & Odintsov 2003, 2006Cognola et al 2008;Elizalde et al 2011;Bamba et al 2008Bamba et al , 2013Bamba et al , 2014Bamba & Odintsov 2015;Chakravarty et al 2013;Chakravarty & Mohanty 2014) have investigated the possibility of the power in R 2 to deviate slightly from two, named the R 2−q inflation, where q ≪ 1. The R 2−q inflation has been shown to be compatible with observations and predicts a larger scalar-to-tensor ratio than that in the R 2 inflation.…”

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confidence: 99%

Constraints on the combined models with R 2 − q $R^{2-q}$ inflation and viable f ( R ) $f(R)$ dark energy

Geng

Lee

Lin

2015

Astrophys Space Sci

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We investigate the observational constraints on the modified gravity, which combines the R 2−q inflation with the power-law (exponential) type of the viable f (R) dark energy models. We discuss the difference between the combined model and R 2−q gravity in the inflationary epoch and obtain the constraints on the deviation power q as well as the parameters in f (R) by using the CosmoMC package. The allowed ranges of the spectral index and tensor-to-scalar ratio from the Planck data are highly restricted, resulting in q < 2.66 × 10 −2 and 2.17 × 10 −2 for the power-law and exponential types of f (R) gravity, respectively.

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Inflationary Cosmology in Modified Gravity Theories

Cited by 341 publications

References 171 publications

Accelerating cosmologies and the phase structure ofF(R)gravity with Lagrange multiplier constraints: A mimetic approach

Accelerating cosmologies and the phase structure ofF(R)gravity with Lagrange multiplier constraints: A mimetic approach

Deformed matter bounce with dark energy epoch

Constraints on the combined models with R 2 − q $R^{2-q}$ inflation and viable f ( R ) $f(R)$ dark energy

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