Inhomogeneous viscous fluids in FRW universe and finite-future time singularities

The purpose of this short review is to describe cosmological models with a linear inhomogeneous time-dependent equation of state (EoS) for the dark energy, when the dark fluid is coupled with dark matter. This may lead to a bounce cosmology. We consider equivalent descriptions in terms of the EoS parameters for an exponential, a power-law, or a double-exponential law for the scale factor $a$. Stability issues are discussed by considering small perturbations around the critical points for the bounce, in the early as well as in the late, universe. The latter part of the paper is concerned with dark energy coupled with dark matter in viscous fluid cosmology. We allow the bulk viscosity $\zeta=\zeta(H,t)$ to be a function of the Hubble parameter and the time, and consider the Little Rip, the Pseudo Rip, and the bounce universe. Analytic expressions for characteristic properties of these cosmological models are obtained.Comment: 13 pages, no figures. Mini-review, to appear in the MDPI journal Univers

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“…Cosmological models in which the modification of gravity is described in terms of a viscous fluid are explored in Refs. [47] and [48].…”

Section: Dark Energy Coupled With Dark Matter In Viscous Fluid Cosmologymentioning

confidence: 99%

Inhomogeneous Dark Fluid and Dark Matter, Leading to a Bounce Cosmology

Brevik

Тимошкин

2015

Universe

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“…Finite-time singularities [1] are timelike singularities which frequently occur in modified gravity cosmologies [1][2][3][4][5][6], and there exist various types of singularities of this sort, with the most phenomenologically severe being the Big Rip. The most phenomenologically "soft" type of singularity is the Type IV [7][8][9][10][11], and the terminology "soft" refers to the fact that the Universe can smoothly pass through these singularities and the physical quantities are finite on these singularities.…”

Section: Introductionmentioning

confidence: 99%

On the expanding phase of a singular bounce and intermediate inflation: The modified gravity description

Oikonomou

2017

Mod. Phys. Lett. A

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We demonstrate that the intermediate inflation scenario, is a singular inflation cosmology, with the singularity at the origin t = 0 being a pressure and energy density singularity and particularly a Type III singularity. Also, we show that the expanding phase of a singular bounce, can be identical to the intermediate inflation scenario, if the singular bounce has a Type III singularity at the origin. For the intermediate inflation scenario we examine the cosmological implications on the power spectrum in the context of various forms of modified gravity. Particularly we calculate the power spectrum in the context of F (R), F (G) Gauss-Bonnet gravity and also for F (T ) gravity and we discuss the viability of each scenario by comparing the resulting spectral index with the latest observational data.

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“…In addition, there are higher-order gravities including the special case f (R) gravity [13][14][15][16][17][18][19], the induced gravity [20,21], the scalar-tensor theories with the special case of Brans-Dicke theory [22][23][24][25][26][27][28], higher-dimensional theories, e.g., the Kaluza-Klein theories [29] and the braneworld scenarios [30]. Also, there are theories that introduce some modifications in the matter component [31,32] or change the geometrical structure, e.g., the non-commutative theories [33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Cosmological and solar system consequences off(R,T)gravity models

2014

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To find more deliberate f (R, T ) cosmological solutions, we proceed our previous paper further by studying some new aspects of the considered models via investigation of some new cosmological parameters/quantities to attain the most acceptable cosmological results. Our investigations are performed by applying the dynamical system approach. We obtain the cosmological parameters/quantities in terms of some defined dimensionless parameters that are used in constructing the dynamical equations of motion. The investigated parameters/quantities are the evolution of the Hubble parameter and its inverse, the "weight function", the ratio of the matter density to the dark energy density and its time variation, the deceleration, the jerk and the snap parameters, and the equation-of-state parameter of the dark energy. We numerically examine these quantities for two general models R + αR −n + √ −T and R log [αR] q + √ −T . All considered models have some inconsistent quantities (with respect to the available observational data), except the model with n = −0.9 which has more consistent quantities than the other ones. By considering the ratio of the matter density to the dark energy density, we find that the coincidence problem does not refer to a unique cosmological event, rather, this coincidence also occurred in the early universe. We also present the cosmological solutions for an interesting model R+c1 √ −T in the non-flat FLRW metric. We show that this model has an attractor solution for the late times, though with w (DE) = −1/2. This model indicates that the spatial curvature density parameter gets negligible values until the present era, in which it acquires the values of the order 10 −4 or 10 −3 . As the second part of this work, we consider the weak-field limit of f (R, T ) gravity models outside a spherical mass immersed in the cosmological fluid. We have found that the corresponding field equations depend on the both background values of the Ricci scalar and the background cosmological fluid density. As a result, we attain the parametrized post-Newtonian (PPN) parameter for f (R, T ) gravity and show that this theory can admit the experimentally acceptable values of this parameter. As a sample, we present the PPN gamma parameter for general minimal power law models, in particular, the model R + c1 √ −T .

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Inhomogeneous viscous fluids in FRW universe and finite-future time singularities

Cited by 31 publications

References 67 publications

Inhomogeneous Dark Fluid and Dark Matter, Leading to a Bounce Cosmology

Inhomogeneous Dark Fluid and Dark Matter, Leading to a Bounce Cosmology

On the expanding phase of a singular bounce and intermediate inflation: The modified gravity description

Cosmological and solar system consequences off(R,T)gravity models

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