Thermodynamics of f(R) Gravity with Disformal Transformation

Chao-Qiang Geng; Wei-Cheng Hsu; Jhih-Rong Lu; Ling-Wei Luo

doi:10.3390/e21020172

Thermodynamics of f(R) Gravity with Disformal Transformation

Entropy ◽

10.3390/e21020172 ◽

2019 ◽

Vol 21 (2) ◽

pp. 172 ◽

Cited By ~ 2

Author(s):

Chao-Qiang Geng ◽

Wei-Cheng Hsu ◽

Jhih-Rong Lu ◽

Ling-Wei Luo

Keyword(s):

Hubble Parameter ◽

Equations Of State ◽

Kinetic Term ◽

Laws Of Thermodynamics ◽

Flrw Universe

We study thermodynamics in f ( R ) gravity with the disformal transformation. The transformation applied to the matter Lagrangian has the form of γ μ ν = A ( ϕ , X ) g μ ν + B ( ϕ , X ) ∂ μ ϕ ∂ ν ϕ with the assumption of the Minkowski matter metric γ μ ν = η μ ν , where ϕ is the disformal scalar and X is the corresponding kinetic term of ϕ . We verify the generalized first and second laws of thermodynamics in this disformal type of f ( R ) gravity in the Friedmann-Lemaître-Robertson-Walker (FLRW) universe. In addition, we show that the Hubble parameter contains the disformally induced terms, which define the effectively varying equations of state for matter.

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PRE-INFLATION IN THE PRESENCE OF CONFORMAL COUPLING

Modern Physics Letters A ◽

10.1142/s0217732304013386 ◽

2004 ◽

Vol 19 (11) ◽

pp. 807-816

Author(s):

APOSTOLOS KUIROUKIDIS ◽

DEMETRIOS B. PAPADOPOULOS

Keyword(s):

Scalar Field ◽

Exact Solutions ◽

Hubble Parameter ◽

Field Potential ◽

Critical Value ◽

Big Bang ◽

Massless Scalar ◽

Massless Scalar Field ◽

Conformal Parameter ◽

Flrw Universe

We consider a massless scalar field, conformally coupled to the Ricci scalar curvature, in the pre-inflation era of a closed FLRW Universe. The scalar field potential can be of the form of the Coleman–Weinberg one-loop potential, which is flat at the origin and drives the inflationary evolution. For positive values of the conformal parameter ξ, less than the critical value ξ c =(1/6), the model admits exact solutions with nonzero minimum scale factor and zero initial Hubble parameter. Thus these solutions can be matched smoothly to the so-called Pre-Big-Bang models. At the end of this pre-inflation era one can match inflationary solutions by specifying the form of the potential and the whole solution is of the class C(1).

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Light of Planck-2015 on Noncanonical Inflation

Advances in High Energy Physics ◽

10.1155/2015/926807 ◽

2015 ◽

Vol 2015 ◽

pp. 1-11 ◽

Cited By ~ 9

Author(s):

Kh. Saaidi ◽

A. Mohammadi ◽

T. Golanbari

Keyword(s):

Scalar Field ◽

Observational Data ◽

Power Law ◽

Hubble Parameter ◽

Field Model ◽

Kinetic Term ◽

Inflationary Scenario ◽

Slow Roll ◽

Power Law Function ◽

Free Parameters

Slow-roll inflationary scenario is considered in noncanonical scalar field model supposing a power-law function for kinetic term and using two formalisms. In the first approach, the potential is picked out as a power-law function, that is, the most common approach in studying inflation. Hamilton-Jacobi approach is selected as the second formalism, so that the Hubble parameter is introduced as a function of scalar field instead of the potential. Employing the last observational data, the free parameters of the model are constrained, and the predicted form of the potential and attractor behavior of the model are studied in detail.

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BIG RIP AND LITTLE RIP SOLUTIONS IN SCALAR MODEL WITH KINETIC AND GAUSS–BONNET COUPLINGS

International Journal of Modern Physics D ◽

10.1142/s0218271812500022 ◽

2012 ◽

Vol 21 (01) ◽

pp. 1250002 ◽

Cited By ~ 25

Author(s):

L. N. GRANDA ◽

E. LOAIZA

Keyword(s):

Scalar Field ◽

Equation Of State ◽

Hubble Parameter ◽

Field Model ◽

Kinetic Term ◽

Late Time ◽

Scalar Model ◽

Big Rip ◽

Specific Choice ◽

Cosmological Solutions

Late time cosmological solutions for scalar field model with kinetic and Gauss–Bonnet couplings are considered. The quintom scenario is realized with and without Big Rip singularity. We find that under specific choice of the Gauss–Bonnet coupling, the model considerably simplifies, giving rise to solutions where the kinetic term is proportional to the square of the Hubble parameter. This allows to reconstruct the model for a suitable cosmological evolution. We considered a solution that matches the observed behavior of the equation of state, while Big Rip singularity may be present or absent, depending on the parameters of the solution. Evolutionary scenarios known as Little Rip, have also been considered.

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Viscous cosmology for early- and late-time universe

International Journal of Modern Physics D ◽

10.1142/s0218271817300245 ◽

2017 ◽

Vol 26 (14) ◽

pp. 1730024 ◽

Cited By ~ 74

Author(s):

Iver Brevik ◽

Øyvind Grøn ◽

Jaume de Haro ◽

Sergei D. Odintsov ◽

Emmanuel N. Saridakis

Keyword(s):

Hubble Parameter ◽

Equations Of State ◽

Point Of View ◽

Late Time ◽

Macroscopic Theory ◽

Viscous Cosmology ◽

Phantom Divide ◽

Special Cases ◽

Ultimate Fate ◽

The Universe

From a hydrodynamicist’s point of view the inclusion of viscosity concepts in the macroscopic theory of the cosmic fluid would appear most natural, as an ideal fluid is after all an abstraction (exluding special cases such as superconductivity). Making use of modern observational results for the Hubble parameter plus standard Friedmann formalism, we may extrapolate the description of the universe back in time up to the inflationary era, or we may go to the opposite extreme and analyze the probable ultimate fate of the universe. In this review, we discuss a variety of topics in cosmology when it is enlarged in order to contain a bulk viscosity. Various forms of this viscosity, when expressed in terms of the fluid density or the Hubble parameter, are discussed. Furthermore, we consider homogeneous as well as inhomogeneous equations of state. We investigate viscous cosmology in the early universe, examining the viscosity effects on the various inflationary observables. Additionally, we study viscous cosmology in the late universe, containing current acceleration and the possible future singularities, and we investigate how one may even unify inflationary and late-time acceleration. Finally, we analyze the viscosity-induced crossing through the quintessence-phantom divide, we examine the realization of viscosity-driven cosmological bounces, and we briefly discuss how the Cardy–Verlinde formula is affected by viscosity.

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A Study on Some Special Forms of Holographic Ricci Dark Energy in Fractal Universe

ISRN High Energy Physics ◽

10.1155/2013/251498 ◽

2013 ◽

Vol 2013 ◽

pp. 1-6 ◽

Cited By ~ 4

Author(s):

Surajit Chattopadhyay ◽

Antonio Pasqua ◽

Sudipto Roy

Keyword(s):

Dark Energy ◽

Energy Density ◽

Deceleration Parameter ◽

Hubble Parameter ◽

Equations Of State ◽

State Parameter ◽

Ricci Dark Energy ◽

Energy Models

We have considered the modified and the extended holographic Ricci dark energy models (MHRDE and EHRDE) in fractal universe. We have assumed a time-like fractal profile v=t−β, where β=4(1−α). We have reconstructed the Hubble parameter H, the energy density, the equations of state parameter w, and the deceleration parameter q for both MHRDE and EHRDE.

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