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In this paper, a possibility of the accelerated expansion of the large scale universe with interacting varying polytropic fluid of a certain type is presented. About a special role of non-gravitational interactions between dark energy and dark matter, in particular, about a possibility of improvement and solution of problems arising in modern cosmology, has been discussed for a long time. This motivates us to consider new models, where non-gravitational interactions between varying polytropic fluid and cold dark matter are allowed. Mainly nonlinear interactions of a specific type is considered, found in recent literature. The present study extends previously obtained results demonstrating that considered new parameterization of dark side of the universe could be supported by available observational data and will present the role of considered non-gravitational interactions in this case. During the study of suggested cosmological models Om analysis is applied. Moreover, with different datasets, including a strong gravitational lensing dataset, the best fit values of the model parameters are obtained using χ 2 analysis. [ABSTRACT FROM AUTHOR]

Abstract We compare supernovae and Baryon Acoustic Oscillations data to the predictions of a cosmological model of interacting dark matter and dark energy. This theoretical model can be derived from the effective field theory of Einstein–Cartan gravity with two scaling exponents δ G and δ Λ , related to the interaction between dark matter and dark energy. We perform a χ 2 fit to the data to compare and contrast it with the standard ΛCDM model. We then explore the range of parameter of the model which gives a better χ 2 than the standard cosmological model. All those results lead to tight constraints on the scaling exponents of the model. Our conclusion is that this class of models, provides a decent alternative to the ΛCDM model. [ABSTRACT FROM AUTHOR]

In this paper, a cosmological model involving interacting varying Chaplygin gas of a specific type and a tachyonic matter is considered to address the problem known as the accelerated expansion of the universe. The study shows that a specific form of the potential and appropriate values of the parameters allows a transition from early tachyonic to late-time tachyonic dark matter with ω T ≈ 0. This point, up to our knowledge, makes the considered cosmological scenario unique in the literature. Moreover, discussion on future finite-time singularities for the considered models finalizes the paper. The study shows that in case of non-interacting model, the fate of universe will be either Type II (The Sudden Singularity), or Type IV (“Generalized Sudden Singularity”) singularity. On the other hand, the consideration of Q = 3 b H ρ d e non-gravitational interaction in addition to Type II and Type IV singularities will induce also Type V (“ ω -singularity”) singularity, while with Q = 3 b q H ρ d e only Type IV singularity will be observed. Moreover, two forms of scale factor have been considered allowing to analytically obtain the behavior of the cosmological parameters without specifying an explicit form of the potential for tachyonic matter. [ABSTRACT FROM AUTHOR]

In this paper, we continue the investigations present in Refs. 1-3. In particular, we extend the theorem proved in Ref. 3 to any massless excitation in a given spherical box. As a first interesting result, we show that it is possible, contrary to the black hole case studied in detail in Refs. 1-3, to build macroscopic configurations with a dark energy equation of state. To this purpose, by requiring a stable configuration, a macroscopic dark fluid is obtained with an internal energy scaling as the volume , but with a fundamental correction looking like motivated by quantum fluctuations. Thanks to the proposition in Sec. 3 (and in Ref. 3 for gravitons), one can depict the dark energy in terms of massless excitations with a discrete spectrum. This fact opens the possibility to test a possible physical mechanism converting usual radiation into dark energy in a macroscopic configuration, also in a cosmological context. In fact, for example, in a Friedmann flat universe with a cosmological constant, particles are marginally trapped at the Hubble horizon for any given comoving observer. [ABSTRACT FROM AUTHOR]

We consider a cosmological model based on a generalization of the equation of state proposed by Nojiri and Odintsov (2004) and Štefančić (2005, 2006). We argue that this model works as a dark fluid model which can interpolate between dust equation of state and the dark energy equation of state. We show how the asymptotic behavior of the equation of state constrained the parameters of the model. The causality condition for the model is also studied to constrain the parameters and the fixed points are tested to determine different solution classes. Observations of Hubble diagram of SNe Ia supernovae are used to further constrain the model. We present an exact solution of the model and calculate the luminosity distance and the energy density evolution. We also calculate the deceleration parameter to test the state of the universe expansion. [ABSTRACT FROM AUTHOR]

In this work, under the assumption that the universe is locally rotationally symmetric (LRS) Bianchi type-II and filled with anisotropic dark fluid (dark energy and dark radiation), we investigate whether the generalized second law of thermodynamics (GSLT) is still valid. We also consider another important condition for LRS Bianchi type-II spacetimes whereby the model expansion θ is proportional to the shear σ, which leads to B = An (where n is a constant and A and B are the metric potentials). Based on this, we derive a general circumstance for the GSLT and find that its validity depends on the anisotropies of both the dark uid and the metric potentials. We conclude that the GSLT still holds at all times even if these two anisotropic conditions are removed from the results. [ABSTRACT FROM AUTHOR]

In this paper, dark energy models of the universe filled with wet dark fluid are constructed in the frame work of LRS Bianchi type-II space-time in General Theory of Relativity. A new equation of state modeled on the equation of state $p = \gamma ( \rho - \rho_{*} )$ , which can describe liquid including water, is used. The exact solutions of Einstein's field equations are obtained in quadrature form and the models corresponding to the cases $\gamma = 0$ and $\gamma = 1$ are discussed in details. [ABSTRACT FROM AUTHOR]

Recently we reported on the condensation of cold, electrostatically trapped dipolar excitons in GaAs bilayer heterostructure into a new, dense and dark collective phase. Here we analyze and discuss in detail the experimental findings and the emerging evident properties of this collective liquid-like phase. We show that the phase transition is characterized by a sharp increase of the number of non-emitting dipoles, by a clear contraction of the fluid spatial extent into the bottom of the parabolic-like trap, and by spectral narrowing. We extract the total density of the condensed phase which we find to be consistent with the expected density regime of a quantum liquid. We show that there are clear critical temperature and excitation power onsets for the phase transition and that as the power further increases above the critical power, the strong darkening is reduced down until no clear darkening is observed. At this point another transition appears which we interpret as a transition to a strongly repulsive yet correlated e - h plasma. Based on the experimental findings, we suggest that the physical mechanism that may be responsible for the transition is a dynamical final-state stimulation of the dipolar excitons to their dark spin states, which have a long lifetime and thus support the observed sharp increase in density. Further experiments and modeling will hopefully be able to unambiguously identify the physical mechanism behind these recent observations. [ABSTRACT FROM AUTHOR]

A unification of dark matter and dark energy in terms of a logotropic perfect dark fluid has recently been proposed, where deviations with respect to the standard ΛCDM model are dependent on a single parameter B . In this paper we show that the requirement that the linear growth of cosmic structures on comoving scales larger than 8 h − 1 Mpc is not significantly affected with respect to the standard ΛCDM result provides the strongest limit to date on the model ( B < 6 × 10 − 7 ), an improvement of more than three orders of magnitude over previous upper limits on the value of B . We further show that this limit rules out the logotropic Unified Dark Energy model as a possible solution to the small scale problems of the Λ CDM model, including the cusp problem of Dark Matter halos or the missing satellite problem, as well as the original version of the model where the Planck energy density was taken as one of the two parameters characterizing the logotropic dark fluid. [ABSTRACT FROM AUTHOR]

If one assumes a particular form of non-minimal coupling, called the conformal coupling, of a perfect fluid with gravity in the fluid-gravity Lagrangian then one gets modified Einstein field equation. In the modified Einstein equation the effect of the non-minimal coupling does not vanish if one works with spacetimes for which the Ricci scalar vanishes. In the present work we use the Schwarzschild metric in the modified Einstein equation, in the presence of non-minimal coupling with a fluid, and find out the energy-density and pressure of the fluid. In the present case the perfect fluid is part of the solution of the modified Einstein equation. We also solve the modified Einstein equation, using the flat spacetime metric and show that in the presence of non-minimal coupling one can accommodate a perfect fluid of uniform energy-density and pressure in the flat spacetime. In both the cases the fluid pressure turns out to be negative. Except these non-trivial solutions it must be noted that the vacuum solutions also remain as trivial valid solutions of the modified Einstein equation in the presence of non-minimal coupling. [ABSTRACT FROM AUTHOR]

We propose a new pressure-parametrization model to explain the accelerated expansion of the late-time Universe by considering the baryon matter and dark contents (dark matter and dark energy) as a unified dark fluid. To realize this model more physically, we reconstruct it with the quintessence and phantom scalar fields, respectively. We use the recent cosmological data to constrain this model, distinguish it from the standard cosmological model and find that the value of the Hubble constant H0 = 68.34-0.92+0.53 supports the global measurement by the Planck satellite at the 1s confidence level. [ABSTRACT FROM AUTHOR]

In this paper we have studied the anisotropic and homogeneous Bianchi Type-I and V universe filled with Interacting Dark Matter and Holographic Dark Energy. The solutions of field equations are obtained for both models under the assumption of linearly varying deceleration parameter which yields dynamical deceleration parameter. It has been observed that the anisotropy of expansion dies out very quickly (soon after inflation) in both models (B-I, B-V). The physical and geometrical parameters for the both models have been obtained and discussed in details. [ABSTRACT FROM AUTHOR]

We propose a heuristic unification of dark matter and dark energy in terms of a single “dark fluid” with a logotropic equation of state P = A ln ⁡ ( ρ / ρ P ) , where ρ is the rest-mass density, ρ P = 5.16 × 10 99 g m − 3 is the Planck density, and A is the logotropic temperature. The energy density ϵ is the sum of a rest-mass energy term ρ c 2 ∝ a − 3 mimicking dark matter and an internal energy term u ( ρ ) = − P ( ρ ) − A = 3 A ln ⁡ a + C mimicking dark energy ( a is the scale factor). The logotropic temperature is approximately given by A ≃ ρ Λ c 2 / ln ⁡ ( ρ P / ρ Λ ) ≃ ρ Λ c 2 / [ 123 ln ⁡ ( 10 ) ] , where ρ Λ = 6.72 × 10 − 24 g m − 3 is the cosmological density and 123 is the famous number appearing in the ratio ρ P / ρ Λ ∼ 10 123 between the Planck density and the cosmological density. More precisely, we obtain A = 2.13 × 10 − 9 g m − 1 s − 2 that we interpret as a fundamental constant. At the cosmological scale, our model fulfills the same observational constraints as the ΛCDM model (they will differ in about 25 Gyrs when the logotropic universe becomes phantom). However, the logotropic dark fluid has a nonzero speed of sound and a nonzero Jeans length which, at the beginning of the matter era, is about λ J = 40.4 pc , in agreement with the minimum size of the dark matter halos observed in the universe. The existence of a nonzero Jeans length may solve the missing satellite problem. At the galactic scale, the logotropic pressure balances the gravitational attraction, providing halo cores instead of cusps. This may solve the cusp problem. The logotropic equation of state generates a universal rotation curve that agrees with the empirical Burkert profile of dark matter halos up to the halo radius. In addition, it implies that all the dark matter halos have the same surface density Σ 0 = ρ 0 r h = 141 M ⊙ / pc 2 and that the mass of dwarf galaxies enclosed within a sphere of fixed radius r u = 300 pc has the same value M 300 = 1.93 × 10 7 M ⊙ , in remarkable agreement with the observations [Donato et al. [10] , Strigari et al. [13] ]. It also implies the Tully–Fisher relation M b / v h 4 = 44 M ⊙ km − 4 s 4 . We stress that our model has no free parameter. [ABSTRACT FROM AUTHOR]

Cosmic Dark Fluid is considered as a non-stationary medium, in which electromagnetic waves propagate, and magneto-electric field structures emerge and evolve. A medium-type representation of the Dark Fluid allows us to involve in its analysis the concepts and mathematical formalism elaborated in the framework of classical covariant electrodynamics of continua, and to distinguish dark analogs of well-known medium-effects, such as optical activity, pyro-electricity, piezo-magnetism, electro- and magneto-striction and dynamo-optical activity. The Dark Fluid is assumed to be formed by a duet of a Dark Matter (a pseudoscalar axionic constituent) and Dark Energy (a scalar element); respectively, we distinguish electrodynamic effects induced by these two constituents of the Dark Fluid. The review contains discussions of 10 models, which describe electrodynamic effects induced by Dark Matter and/or Dark Energy. The models are accompanied by examples of exact solutions to the master equations, correspondingly extended; applications are considered for cosmology and space-times with spherical and pp-wave symmetries. In these applications we focused the attention on three main electromagnetic phenomena induced by the Dark Fluid: first, emergence of Longitudinal Magneto-Electric Clusters; second, generation of anomalous electromagnetic responses; third, formation of Dark Epochs in the Universe history. [ABSTRACT FROM AUTHOR]

In this paper, we will consider a phenomenological model of a dark fluid that is able to explain an accelerated expansion of our low redshift universe and the phase transition to this accelerated expanding universe. Recent developments in modern cosmology towards understanding of the accelerated expansion of the large scale universe involve various scenarios and approaches. Among these approaches, one of well-known and accepted practice is modeling of the content of our universe via dark fluid. There are various models of dark energy fluid actively studied in recent literature and polytropic gas is among them. In this work, we will consider a varying polytropic gas which is a phenomenological modification of polytropic gas. Our model of varying polytropic dark fluid has been constructed to analogue to a varying Chaplygin gas actively discussed in the literature. We will consider interacting models, where dark matter is a pressureless fluid, to have a comprehensive picture. Phase space analysis is an elegant mathematical tool to earn general understanding of large scale universe and easily see an existence of a solution to cosmological coincidence problem. Imposing some constraints on parameters of the models, we found late time attractors for each case analytically. Cosmological consequences for the obtained late time attractors are discussed. [ABSTRACT FROM AUTHOR]

Cosmography represents an important branch of cosmology which aims to describe the universe without the need of postulating a priori any particular cosmological model. All quantities of interest are expanded as a Taylor series around here and now, providing in principle, a way of directly matching with cosmological data. In this way, cosmography can be regarded a model-independent technique, able to fix cosmic bounds, although several issues limit its use in various model reconstructions. The main purpose of this review is to focus on the key features of cosmography, emphasizing both the strategy for obtaining the observable cosmographic series and pointing out any drawbacks which might plague the standard cosmographic treatment. In doing so, we relate cosmography to the most relevant cosmological quantities and to several dark energy models. We also investigate whether cosmography is able to provide information about the form of the cosmological expansion history, discussing how to reproduce the dark fluid from the cosmographic sound speed. Following this, we discuss limits on cosmographic priors and focus on how to experimentally treat cosmographic expansions. Finally, we present some of the latest developments of the cosmographic method, reviewing the use of rational approximations, based on cosmographic Padé polynomials. Future prospects leading to more accurate cosmographic results, able to better reproduce the expansion history of the universe, are also discussed in detail. [ABSTRACT FROM AUTHOR]

The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the Einstein cosmological term. This allows to describe a vacuum in general setting by dynamical vacuum dark fluid, presented by a variable cosmological term with the reduced symmetry which makes vacuum dark fluid essentially anisotropic and allows it to be evolving and clustering. The relevant regular solutions to the Einstein equations describe regular cosmological models with time-evolving and spatially inhomogeneous vacuum dark energy, and compact vacuum objects generically related to a dark energy through the de Sitter vacuum interior: regular black holes, their remnants and self-gravitating vacuum solitons - which can be responsible for observational effects typically related to a dark matter. The mass of objects with de Sitter interior is generically related to vacuum dark energy and to breaking of space-time symmetry. [ABSTRACT FROM AUTHOR]

In this work, we model galactic haloes describing the dark matter as a non-zero pressure fluid and derive, not impose, a dark matter equation of state by using observational data of the rotation curves of galaxies. In order to reach hydrostatic equilibrium, as expected for the halo, it is mandatory that dark fluid's pressure should not be zero. The equation of state is obtained by solving the matter-geometry system of equations assuming different dark matter density or rotational velocity profiles. The resulting equations of state are, in general, different to a barotropic equation of state. The free parameters of the equation of state are fixed by fitting the observed rotational velocities of a set of galaxies. [ABSTRACT FROM AUTHOR]

Anisotropic dark energy cosmological models are constructed in the frame work of generalised Brans-Dicke theory with a self-interacting potential. A unified dark fluid characterised by a linear equation of state is considered as the source of dark energy. The shear scalar is considered to be proportional to the expansion scalar simulating an anisotropic relationship among the directional expansion rates. The dynamics of the universe in the presence of a unified dark fluid in anisotropic background have been discussed. The presence of an evolving scalar field makes it possible to get an accelerating phase of expansion even for a linear relationship among the directional Hubble rates. It is found that the anisotropy in expansion rates does not affect the scalar field, the self-interacting potential, but it controls the non-evolving part of the Brans-Dicke parameter. [ABSTRACT FROM AUTHOR]

In the present work, flat FRW model of the universe is considered to be an isolated open thermodynamical system where non-equilibrium prescription has been studied using the mechanism of particle creation. In the perspective of recent observational evidences, the matter distribution in the universe is assumed to be dominated by dark matter and dark energy. The dark matter is chosen as dust while for dark energy, the following choices are considered: (i) Perfect fluid with constant equation of state and (ii) Holographic dark energy. In both the cases, the validity of generalized second law of thermodynamics (GSLT) which states that the total entropy of the fluid as well as that of the horizon should not decrease with the evolution of the universe, has been examined graphically for universe bounded by the event horizon. It is found that GSLT holds in both the cases with some restrictions on the interacting coupling parameter. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new unified dark fluid (UDF) model with equation of state (EoS) w( a)=− α/( β a+1), which includes the generalized Chaplygin gas model (gGg) as its special case, where α, β and n are three positive numbers. It is clear that this model reduces to the gCg model with EoS w( a)=− B/( B+(1− B) a), when α=1, β=(1− B)/ B and n=3(1+ α). By combination the cold dark matter and the cosmological constant, one can coin a EoS of unified dark fluid in the form of w( a)=−1/(1+(1−Ω) a/Ω). With this observations, our proposed EoS provides a possible deviation from ΛCDM model when the model parameters α and n deviate from 1 and 3 respectively. By using the currently available cosmic observations from type Ia supernovae (SN Ia) Union2.1, baryon acoustic oscillation (BAO) and cosmic microwave background radiation (CMB), we test the viability of this model and detect the possible devotion from the ΛCDM model. The results show that the new UDF model fits the cosmic observation as well as that of the ΛCDM model and no deviation is found from the ΛCDM model in 3 σ confidence level. However, our new UDF model can give a non-zero sound speed, as a contrast, which is zero for the ΛCDM model. We expect the large structure formation information can distinct the new UDF model from the ΛCDM model. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the five-dimensional Kaluza-Klein space time with wet dark fluid (WDF), which is a candidate for dark energy (DE), in the framework of f(R, T) gravity. R and T denote the Ricci scalar and the trace of the energy-momentum tensor, respectively (Harko et al. Phys. Rev. D, 84, 024020 (2011)). We have used equation of state in the form of WDF for the DE component of the universe. It is modeled on the equation of state p =ω(p-p*). With the help of the power law and exponential law of volumetric expansion, we have derived the exact solutions of the corresponding field equations. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and very late time of the universe. It is concluded that the model obtained here shows that even in the presence of WDF, the universe indicates accelerated expansion of the universe. [ABSTRACT FROM AUTHOR]

A five dimensional Kaluza-Klein space time is considered with wet dark fluid (WDF) source in the framework of f(R, T) gravity, where R is the Ricci scalar and T is the trace of the energy-momentum tensor proposed by Harko et al. (Phys. Rev. D 84, 024020, (2011)). A new equation of state in the form of WDF has been used for dark energy (DE) component of the universe. It is modeled on the equation of state p = ω(ρ - ρ*) which can be describing a liquid, for example water. The exact solutions to the corresponding field equations are obtained for power law and exponential law of the volumetric expansion. The geometrical and physical parameters for both the models are studied. The model obtained here may represent the inflationary era in the early universe and the very late time of the universe. This model obtained here shows that even in the presence of wet dark fluid, the universe indicates accelerated expansion of the universe. [ABSTRACT FROM AUTHOR]

A cosmological model with an inhomogeneous viscous dark fluid coupled with dark matter in a flat Friedmann-Robertson-Walker (FRW) universe is investigated. The influence of dark matter on the behavior of an inhomogeneous viscous fluid of this kind, responsible for cosmic acceleration and for the appearance of different types of singularities, is analyzed in detail. In particular, the critical points corresponding to the solutions of the background equations in a useful approximation are obtained explicitly. [ABSTRACT FROM AUTHOR]

A non-equilibrium thermodynamic analysis has been done for the interacting dark fluid in the universe bounded by the event horizon. From observational evidences it is assumed that at present the matter in the universe is dominated by two dark sectors-dark matter and dark energy (DE). The mutual interaction among them results in spontaneous heat flow between the horizon and the fluid system and the thermal equilibrium will no longer hold. In the present work, the dark matter is chosen in the form of dust while the DE is chosen as a perfect fluid with constant equation of state in one case and holographic DE model is chosen in the other. Finally, validity of the generalized second law of thermodynamics has been examined in both cases. [ABSTRACT FROM AUTHOR]

We investigate cosmological models with a linear inhomogeneous time-dependent equation-of-state (EoS) for the dark energy, coupled with dark matter, leading to a bounce cosmology. Equivalent descriptions in terms of the EoS parameters for an ex-ponential, a power-law, or a double exponential form of the scale factor a is obtained. The stability of the solutions is explored, by considering small perturbations around the critical points for the bounce in the early and in the late-time universe. [ABSTRACT FROM AUTHOR]

In this paper, we test the spherical collapse of a viscous unified dark fluid (VUDF) which has constant adiabatic sound speed and show the nonlinear collapse for VUDF, baryons, and dark matter, which are important in forming the large-scale structure of our Universe. By varying the values of the model parameters $$\alpha $$ and $$\zeta _{0}$$ , we discuss their effects on the nonlinear collapse of the VUDF model, and we compare its result to the $$\Lambda $$ CDM model. The results of the analysis show that, within the spherical top-hat collapse framework, larger values of $$\alpha $$ and smaller values of $$\zeta _{0}$$ make the structure formation earlier and faster, and the other collapse curves are almost distinguished with the curve of $$\Lambda $$ CDM model if the bulk viscosity coefficient $$\zeta _{0}$$ is less than $$10^{-3}$$ . [ABSTRACT FROM AUTHOR]

In this paper, we continue our previous work of studying viscous generalized Chaplygin gas as a unified dark fluid but the bulk viscosity perturbations. By using the currently available cosmic observational data from SNLS3, BAO, HST, and recently released Planck, we obtain a constraint on the bulk viscosity coefficient: $$\zeta _0=0.0000138_{- 0.0000105- 0.0000138- 0.0000138}^{+ 0.00000614+ 0.0000145+ 0.0000212}$$ in $$1, 2, 3\sigma $$ regions, respectively, via the Markov Chain Monte Carlo method. The result shows that when considering perturbations of the bulk viscosity, the current cosmic observations favor a smaller bulk viscosity coefficient. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated Bianchi type VI h, II and III cosmological model with wet dark fluid in scale invariant theory of gravity, where the matter field is in the form of perfect fluid and with a time dependent gauge function (Dirac gauge). A non-singular model for the universe filled with disorder radiation is constructed and some physical behaviors of the model are studied for the feasible VI h ( h=1) space-time. [ABSTRACT FROM AUTHOR]

Specific dark energy models with a linear inhomogeneous time-dependent equation of state, within the framework of 4d Friedman-Robertson-Walker (FRW) cosmology, are investigated. It is demonstrated that such 4d inhomogeneous fluid models may lead to a turbulence FRW cosmology. Both one-component and two-component models from 4d inhomogeneous dark fluid models are considered. In the one-component model the universe may develop from a viscous era with, for instance, a constant bulk viscosity, into a turbulent era. In the two-component model the fluid can be decomposed into two components, one non-turbulent (ideal) and another turbulent part, obeying two different equations of state. Conditions for the appearance of the turbulent dark energy universe in terms of the parameters in the equation of state (EoS) without introducing the turbulence concept explicitly are obtained. An equivalent description in terms of an inhomogeneous fluid for the viscous Little Rip (LR) cosmology is also developed. [ABSTRACT FROM AUTHOR]

Specific dark energy models with linear inhomogeneous time-dependent equation of state, within the framework of 4d Friedman-Robertson-Walker (FRW) cosmology, are investigated. It is demonstrated that the choice of such 4d inhomogeneous fluid models may lead to a brane FRW cosmology without any explicit account of higher dimensions at all. Effectively, we thus obtain a brane dark energy universe without introducing the brane concept explicitly. Several examples of brane Rip cosmology arising from 4d inhomogeneous dark fluid models are given. [ABSTRACT FROM AUTHOR]

In this paper, we have constructed a five dimensional LRS Bianchi type I cosmological model with wet dark fluid (WDF) in general relativity with the matter field described as bulk viscosity. It is found that in presence of bulk viscosity an inflationary effective stiff fluid cosmological model is obtained, whereas in absence of bulk viscosity the wet dark fluid degenerate to stiff fluid. Some physical and geometrical properties of the model are also discussed. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the role of wet dark fluid (WDF) in Kantowski-Sachs space-time in the general theory of relativity. In this theory, we solved the field equations for the case where ρWDF = -2pWDF . Various physical and geometrical properties of the model are also discussed. [ABSTRACT FROM AUTHOR]

We studied the Bianchi type-V universe filled with dark energy (DE) from a wet dark fluid (WDF) in the framework of f( R, T) gravity (Harko in Phys. Rev. D 84:024020, ). A new equation of state for the dark energy (DE) component of the universe has been used. It is modeled on the equation of state p= w( ρ− ρ) which can be describing a liquid, for example water. The exact solutions to the corresponding field equations are obtained for exponential and power-law volumetric expansion. It is observed that the universe can approach to isotropy monotonically even in the presence of wet dark fluid. Also we have discussed the well-known astrophysical phenomena, namely the look-back time, proper distance, the luminosity distance and angular diameter distance with redshift. [ABSTRACT FROM AUTHOR]

In this paper, we test the spherical collapse of a unified dark fluid (UDF) which has constant adiabatic sound speed. By choosing the different values of model parameters B and α, we show the non-linear collapse for UDF and baryons which are considered for their formation of the large scale structure of our Universe. The analyzed results show that larger values of α and B make the structure formation faster and earlier. [ABSTRACT FROM AUTHOR]

We examine the evolution of an inhomogeneous mixture of non-relativistic pressureless cold dark matter (CDM), coupled to dark energy (DE) characterised by the equation of state parameter w<-1/3, with the interaction term proportional to the DE density. This coupled mixture is the source of a spherically symmetric Lemaître-Tolman-Bondi (LTB) metric admitting an asymptotic Friedman-Lemaître-Robertson-Walker (FLRW) background. Einstein’s equations reduce to a 5-dimensional autonomous dynamical system involving quasi-local variables related to suitable averages of covariant scalars and their fluctuations. The phase space evolution around the critical points (past/future attractors and five saddles) is examined in detail. For all parameter values and both directions of energy flow (CDM to DE and DE to CDM) the phase space trajectories are compatible with a physically plausible early cosmic times behaviour near the past attractor. This result compares favourably with mixtures with interaction driven by the CDM density, whose past evolution is unphysical for DE to CDM energy flow. Numerical examples are provided describing the evolution of an initial profile that can be associated with idealised structure formation scenarios. [ABSTRACT FROM AUTHOR]