Showing papers on "Big Rip published in 2017"
TL;DR: In this paper, a holographic dark energy (HDE) model is proposed, in which the future event horizon is chosen as the characteristic length scale and the theoretical explorations and the observational constraints for this model are discussed.
249 citations
TL;DR: In this paper, the authors discuss a variety of topics in cosmology when it is enlarged in order to contain a bulk viscosity, when expressed in terms of the fluid density or the Hubble parameter.
Abstract: 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.
160 citations
TL;DR: In this paper, the generalized holographic dark energy model is proposed, where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives.
Abstract: We propose the generalized holographic dark energy model where the infrared cutoff is identified with the combination of the FRW universe parameters: the Hubble rate, particle and future horizons, cosmological constant, the universe lifetime (if finite) and their derivatives. It is demonstrated that with the corresponding choice of the cutoff one can map such holographic dark energy to modified gravity or gravity with a general fluid. Explicitly, F(R) gravity and the general perfect fluid are worked out in detail and the corresponding infrared cutoff is found. Using this correspondence, we get realistic inflation or viable dark energy or a unified inflationary-dark energy universe in terms of covariant holographic dark energy.
135 citations
TL;DR: In this paper, the evolution of the Hubble radius and the issue of primordial cosmological perturbations in detail were investigated, and the viability of the singular bounce model was discussed.
Abstract: An alternative to the Big Bang cosmologies is obtained by the Big Bounce cosmologies. In this paper, we study a bounce cosmology with a Type IV singularity occurring at the bouncing point in the context of F(R) modified gravity. We investigate the evolution of the Hubble radius and we examine the issue of primordial cosmological perturbations in detail. As we demonstrate, for the singular bounce, the primordial perturbations originating from the cosmological era near the bounce do not produce a scale-invariant spectrum and also the short wavelength modes after these exit the horizon, do not freeze, but grow linearly with time. After presenting the cosmological perturbations study, we discuss the viability of the singular bounce model, and our results indicate that the singular bounce must be combined with another cosmological scenario, or should be modified appropriately, in order that it leads to a viable cosmology. The study of the slow-roll parameters leads to the same result indicating that the singular bounce theory is unstable at the singularity point for certain values of the parameters. We also conformally transform the Jordan frame singular bounce, and as we demonstrate, the Einstein frame metric leads to a Big Rip singularity. Therefore, the Type IV singularity in the Jordan frame becomes a Big Rip singularity in the Einstein frame. Finally, we briefly study a generalized singular cosmological model, which contains two Type IV singularities, with quite appealing features.
54 citations
TL;DR: In this paper, the exact solutions of the field equations are derived with linearly time varying deceleration parameter, which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology.
Abstract: Locally rotationally symmetric (LRS) Bianchi type-I magnetized strange quark matter (SQM) cosmological model has been studied based on f(R, T) gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter, which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model begins with big bang and ends with a Big Rip. The transition of the deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. [Astrophys. J. 835, 26 (2017)]. The well-known Hubble parameter H(z) and distance modulus μ(z) are discussed with redshift.
51 citations
TL;DR: A preliminary analysis of the 3-form dark energy (DE) models with interactions in the dark sector in light of the recently released data by SDSS~III on the measurement of the linear growth rate of structure is made.
47 citations
TL;DR: In this article, the exact solutions of the field equations are derived with linearly time varying deceleration parameter which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology.
Abstract: LRS (Locally Rotationally symmetric) Bianchi type-I magnetized strange quark matter cosmological model have been studied based on $f(R,T)$ gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model start with big bang and ends with a Big Rip. The transition of deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. in 2017. The well known Hubble parameter $H(z)$ and distance modulus $\mu(z)$ are discussed with redshift.
42 citations
TL;DR: In this article, the authors analyzed characteristic properties of two different cosmological models: (i) a one-component dark energy model where the bulk viscosity ζ is associated with the fluid as a whole, and (ii) a two-component model where ζ was associated with a dark matter component ρm only, the dark energy component considered inviscid.
Abstract: We analyze characteristic properties of two different cosmological models: (i) a one-component dark energy model where the bulk viscosity ζ is associated with the fluid as a whole, and (ii) a two-component model where ζ is associated with a dark matter component ρm only, the dark energy component considered inviscid. Shear viscosity is omitted. We assume throughout the simple equation-of-state p = wρ with w a constant. In the one-component model, we consider two possibilities, either to take ζ proportional to the scalar expansion (equivalent to the Hubble parameter), in which case the evolution becomes critically dependent on the value of the small constant α = 1 + w and the magnitude of ζ, or we consider the case ζ = const., where a de Sitter final stage is reached in the future. In the two-component model, we consider only the case where the dark matter viscosity ζm is proportional to the square of ρm, where again a de Sitter form is found in the future. In this latter case, the formalism is supplemented by a phase space analysis. As a general result of our considerations, we suggest that a value ζ0 ∼ 106Pa ⋅s for the present viscosity is reasonable, and that the two-component model seems to be favored.
42 citations
TL;DR: In this article, the effects of gravity's rainbow and massive gravity's generalization on the evolution of the universe have been investigated and all the essential conditions for having a nonsingular universe and its effects on such criteria are determined.
39 citations
TL;DR: In this article, the authors propose an interpretation of the expansion and acceleration of the universe from an information theoretic viewpoint and obtain the time evolution of the configuration entropy of the mass distribution in a static universe and show that the process of gravitational instability leads to a rapid dissipation of configuration entropy during the growth of the density fluctuations making such a universe entropically unfavourable.
Abstract: We propose an interpretation of the expansion and acceleration of the Universe from an information theoretic viewpoint We obtain the time evolution of the configuration entropy of the mass distribution in a static Universe and show that the process of gravitational instability leads to a rapid dissipation of configuration entropy during the growth of the density fluctuations making such a Universe entropically unfavourable We find that in an expanding Universe, the configuration entropy rate is governed by the expansion rate of the Universe and the growth rate of density fluctuations The configuration entropy rate becomes smaller but still remains negative in a matter dominated Universe and eventually becomes zero at some future time in a $\Lambda$ dominated Universe The configuration entropy may have a connection to the dark energy and possibly plays a driving role in the current accelerating expansion of the Universe leading the Universe to its maximum entropy configuration
30 citations
TL;DR: In this paper, the authors carried out an analysis of the cosmological perturbations in general relativity for three different models which are good candidates to describe the current acceleration of the Universe.
Abstract: We study scenarios of parallel cyclic multiverses which allow for a different evolution of the physical constants, while having the same geometry. These universes are classically disconnected, but quantum-mechanically entangled. Applying the thermodynamics of entanglement, we calculate the temperature and the entropy of entanglement. It emerges that the entropy of entanglement is large at big bang and big crunch singularities of the parallel universes as well as at the maxima of the expansion of these universes. The latter seems to confirm earlier studies that quantum effects are strong at turning points of the evolution of the universe performed in the context of the timeless nature of the Wheeler-DeWitt equation and decoherence. On the other hand, the entropy of entanglement at big rip singularities is going to zero despite its presumably quantum nature. This may be an effect of total dissociation of the universe structures into infinitely separated patches violating the null energy condition. However, the temperature of entanglement is large/infinite at every classically singular point and at maximum expansion and seems to be a better measure of quantumness.
TL;DR: In this paper, a phantom solution in the framework of the causal Israel-Stewart (IS) formalism is discussed and the behavior of the thermodynamic parameters associated to this solution, like the temperature, rate of entropy, entropy, relaxation time, effective pressure and effective EoS are evaluated.
TL;DR: In this article, the authors studied wormholes solutions based on fractional action cosmology and derived wormholes wave function in a closed Friedmann-Robertson-Walker (FRW) universe and found that a wormhole can survive in the presence of quantum effects only if the expansion of the universe is accelerated with time.
Abstract: In this work we study wormholes solutions based on fractional action cosmology. We discuss cosmic dynamics of the universe in the presence of wormhole and wormhole wave function in closed Friedmann–Robertson–Walker (FRW) universe. We have observed that cosmic acceleration with traversable wormhole may be realized without the need of exotic matter like dark and phantom energy unless the scale factor of the universe obeys a power law dominated by a negative fractional parameter, which is constrained from type Ia supernovae data. Besides, we have derived wormholes wave function in a closed FRW universe and we have found that a wormhole can survive in the presence of quantum effects only if the expansion of the universe is accelerated with time.
TL;DR: In this article, a quantum analysis of the EiBI theory with a matter field was carried out, which, from a classical point of view, would inevitably lead to a universe that ends with either Little Rip (LR) or Little Sibling of the Big Rip (LSBR).
TL;DR: In this article, a dynamical system investigation of interacting dark energy models (quintessence and phantom) in the framework of loop quantum cosmology by taking into account a broad class of self-interacting scalar field potentials is presented.
Abstract: The present work deals with the dynamical system investigation of interacting dark energy models (quintessence and phantom) in the framework of loop quantum cosmology by taking into account a broad class of self-interacting scalar field potentials. The main reason for studying potentials beyond the exponential type is to obtain additional critical points which can yield more interesting cosmological solutions. The stability of critical points and the asymptotic behavior of the phase space are analyzed using dynamical system tools and numerical techniques. We study two classes of interacting dark energy models and consider two specific potentials as examples: the hyperbolic potential and the inverse power-law potential. We find a rich and interesting phenomenology, including the avoidance of big rip singularities due to loop quantum effects, smooth and nonlinear transitions from matter domination to dark energy domination, and finite periods of phantom domination with dynamical crossing of the phantom barrier.
TL;DR: In this paper, a simple method for the description of the big bang was proposed for the flat Friedmann universe, which gives the same results as more complicated methods, using Weyl symmetry or the transitions between the Jordan and Einstein frames.
Abstract: We consider a rather simple method for the description of the big bang--big crunch cosmological singularity crossing. For the flat Friedmann universe this method gives the same results as more complicated methods, using Weyl symmetry or the transitions between the Jordan and Einstein frames. It is then easily generalized for the case of a Bianchi-I anisotropic universe. We also present early-time and late-time asymptotic solutions for a Bianchi-I universe, filled with a conformally coupled massless scalar field.
TL;DR: In this article, the authors investigated the anisotropic behavior of the accelerating universe in Bianchi V spacetime in the framework of General Relativity (GR), where the matter field is of two non-interacting fluids, i.e. the usual string fluid and dark energy (DE) fluid.
Abstract: In this paper, we have investigated the anisotropic behavior of the accelerating universe in Bianchi V spacetime in the framework of General Relativity (GR). The matter field we have considered is of two non-interacting fluids, i.e. the usual string fluid and dark energy (DE) fluid. In order to represent the pressure anisotropy, the skewness parameters are introduced along three different spatial directions. To achieve a physically realistic solutions to the field equations, we have considered a scale factor, known as hybrid scale factor, which is generated by a time-varying deceleration parameter. This simulates a cosmic transition from early deceleration to late time acceleration. It is observed that the string fluid dominates the universe at early deceleration phase but does not affect nature of cosmic dynamics substantially at late phase, whereas the DE fluid dominates the universe in present time, which is in accordance with the observations results. Hence, we analyzed here the role of two fluids in ...
07 Jun 2017
TL;DR: In this article, the relationship between intrinsic pressure of SQS (dark energy's repulsive force) and gravity, described as an inflow of dark energy into massive particles, causing a negative pressure gradient around massive bodies, is analyzed.
Abstract: We assume that dark energy and dark matter filling up the whole cosmic space behave as a special superfluid, here named “superfluid quantum space.” We analyze the relationship between intrinsic pressure of SQS (dark energy's repulsive force) and gravity, described as an inflow of dark energy into massive particles, causing a negative pressure gradient around massive bodies. Since no superfluid has exact zero viscosity, we analyze the consequences of SQS’s viscosity on light propagation, and we show that a static Universe could be possible, by solving a modified Navier-Stokes equation. Indeed, Hubble’s law may actually refer to tired light, though described as energy loss due to SQS’s nonzero viscosity instead of Compton scattering, bypassing known historical problems concerning tired light. We see that SQS’s viscosity may also account for the Pioneer anomaly. Our evaluation gives a magnitude of the anomalous acceleration aP = HΛc = 8.785 10 10 ms . Here, HΛ is the Hubble parameter loaded by the cosmological constant Λ. Furthermore, the vorticity equation stemming from the modified Navier-Stokes equation gives a solution for flat profile of the orbital speed of spiral galaxies and discloses what one might call a breathing of galaxies due to energy exchange between the galactic vortex and dark energy.
TL;DR: In this article, the authors present a phantom solution with a big rip singularity in a non-linear regime of the Israel-Stewart formalism, which allows to cross the phantom divide without evoking an exotic matter fluid and the effective EoS parameter is always lesser than −1 and constant in time.
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TL;DR: In this paper, the authors tackle the vast question of generating accelerated periods of expansion of the universe and propose a model based on the idea of an accelerated expanding universe being a mirage due to inhomogeneities disposed in a fractal way.
Abstract: This thesis tackles the vast question of generating accelerated periods of expansion of the universe. Models loosely related were developed in the early and late universe. In the early universe, generalizations of the Schwinger effect were developed in curved (de Sitter) space and some backreaction effects were estimated. In the late universe, a fractal model was developed and confronted to supernovae data. This relies on the idea of an accelerated expanding universe being nothing but a mirage due to inhomogeneities disposed in a fractal (in this particular model) way. Finally a model of interacting energy based on an Einstein-Cartan gravitational theory was phenomenologically investigated.
TL;DR: In this article, the authors presented a super inflation mechanism composed of three phase regions which describes the evolution of the early universe and verified this inflationary mechanism by using the spectral index parameter and the scalar tensor ratio.
Abstract: There are various mechanisms that explain both the inflationary epoch of the early universe and a unification of this epoch with the other stages of the universe. In this study, we show all the expansion history of the universe and transition among of them in a single form by using the theoretical framework of $F ( T, T_{G} ) $
gravity in the context of the FRW (Friedmann-Robertson-Walker) universe. According to a particular model we obtain the unified solutions of the field equations. Without using any scalar field description we especially present the super inflation mechanism composed of three phase regions which describes the evolution of the early universe. The mechanism begins with a vacuum state and then follows a super accelerated period where there are two regions. The first continues in a quintessential field, and the second is a region where the radiation is created. Furthermore, we verified this inflationary mechanism by using the spectral index parameter and the scalar tensor ratio, i.e., $n_{s}$
, $r$
, and calculated the ratio of radiation emergent from the quintessence field. This creation should be in a certain rate in the early universe otherwise we show that the universe cannot survive and continue to expand. Also, we have obtained a phantom solution of the model that shows two regions which are compatible with the recent cosmological observations. In one respect, it is observed that the late time expansion of the universe is similar to the early time inflation.
TL;DR: In this paper, the authors compare three different models where the dark energy content is described by a perfect fluid with an equation of state w ≲ − 1 which can evolve or not.
Abstract: The ΛCDM paradigm, characterised by a constant equation of state w = − 1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state is close to but slightly smaller than − 1 . In this regard, we focus on three different models where the dark energy content is described by a perfect fluid with an equation of state w ≲ − 1 which can evolve or not. The three proposals show very similar behaviour at present, while the asymptotic evolution of each model drives the Universe to different abrupt events known as (i) Big Rip; (ii) Little Rip (LR); and (iii) Little Sibling of the Big Rip. With the aim of comparing these models and finding possible imprints in their predicted matter distribution, we compute the matter power spectrum and the growth rate f σ 8 . We conclude that the model which induces a LR seems to be favoured by observations.
TL;DR: In this paper, the transition probability for the decay of a massive scalar particle in a stiff matter dominated universe has been calculated and it is shown that due to the precence of a gravitational field, the decay rate is smaller and the lifetime of the particles is longer compared to flat space.
Abstract: In the presence of a gravitational field decay rates may significantly differ from flat space equivalent. By studying mutually interacting quantum fields the decay rates can be calculated on a given spacetime. This paper presents the calculation of the transition probability for the decay of a massive scalar particle in a stiff matter dominated universe. We find that due to the precence of a gravitational field a finite correction to the transition probability is added which depends inversely on the mass. Moreover the decay rate is smaller and lifetime of the particles is longer compared to flat space. The mass dependence is such that the lifetime of lighter particles is prolonged more compared to heavier particles. This result may be of significance when studying cosmological situations involving stiff matter.
TL;DR: In this paper, a model of nonlinear electrodynamics with a dimensional parameter $\beta$ is considered and it is demonstrated that after the universe inflation the universe decelerates approaching the Minkowski spacetime.
Abstract: A model of nonlinear electrodynamics with a dimensional parameter $\beta$ is considered. Electromagnetic fields are the source of the gravitation field and inflation of the universe. We imply that the universe is filled by stochastic magnetic fields. It is demonstrated that after the universe inflation the universe decelerates approaching the Minkowski spacetime. We evaluate the spectral index, the tensor-to-scalar ratio, and the running of the spectral index which approximately agree with the PLANK and WMAP data.
01 Jan 2017
TL;DR: In this paper, the authors hypothesize a closed universe belonging to the oscillatory class, where all the points are replaced by straight line segments: what we perceive as being a point is actually a straight line segment crossing the center of a four-dimensional ball.
Abstract: We hypothesize a closed Universe belonging to the oscillatory class. More precisely, we postulate a Universe that evolves following a simple harmonic motion whose pulsation is equal to the ratio between the speed of light and the mean radius of curvature. The existence of at least a further spatial dimension is contemplated. Although the space we are allowed to perceive is curved, since it is identifiable with a hypersphere whose radius depends on our state of motion, the Universe in its entirety, herein assimilated to a four-dimensional ball, is to be considered as being flat. All the points are replaced by straight line segments: In other terms, what we perceive as being a point is actually a straight line segment crossing the center of the above mentioned four-dimensional ball. In the light of these hypotheses, we can easily obtain the identity that represents the so called relativistic energy. In this paper we discuss, more thoroughly than elsewhere, the deduction of the so called mass-energy equivalence. Moreover, by carrying out a simple comparison with the way in which we perceive a bi-dimensional surface, the noteworthy concept of dimensional thickness is introduced.
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TL;DR: In this article, a new cosmological model is proposed for the dynamics of the universe and the formation and evolution of galaxies and it is shown that the matter of the Universe contracts and expands in cycles, and that galaxies in a particular cycle may have imprints from the previous cycle.
Abstract: A new cosmological model is proposed for the dynamics of the Universe and the formation and evolution of galaxies. It is shown that the matter of the Universe contracts and expands in cycles, and that galaxies in a particular cycle may have imprints from the previous cycle. It is proposed that RHIC’s liquid gets trapped in the cores of galaxies in the beginning of each cycle and is liberated throughout time and is, thus, the power engine of AGNs. It is also proposed that the large-scale structure is a permanent property of the Universe, and thus, it is not created. It is proposed that spiral galaxies and elliptical galaxies are formed by mergers of nucleon vortices (vorteons) at the time of the big squeeze and immediately afterwards and that the merging process, in general, lasts an extremely long time, of many billion years. The origin of quasars is explained and the evaporation rate of RHIC’s liquid is calculated. The large mass at the center of quasar PDS 456 is calculated and agrees in order of magnitude with that attributed to a supposed black hole. It is concluded that the Universe is eternal and that space should be infinite or almost.
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TL;DR: Debate over the Hubble constant, the expansion rate of the universe, has exploded again, and the dispute suggests a missing ingredient may be fueling the growth of the universes.
Abstract: Debate over the Hubble constant, the expansion rate of the universe, has exploded again. Astronomers had mostly settled on a number using a classical technique—the "distance ladder," or astronomical observations from the local universe on out. But these values conflict with cosmological estimates made from maps of the early universe and adjusted to the present day. The dispute suggests a missing ingredient may be fueling the growth of the universe.
TL;DR: In this article, it is shown that in the early Universe the orientation of its spin is random, and the cosmological principle is satisfied, and this result is naturally consistent with the CMBisotropy.
Abstract: We find the probability density distribution of torque orientations in the Universe for the entire period of its evolution. It is shown that in the early Universe the orientation of its spin is random, and the cosmological principle is satisfied. This result is naturally consistent with the CMBisotropy. In the modern Universe the rotation axis direction becomes anisotropic, and the cosmological principle, strictly speaking, is not satisfied. This is confirmed by the large-scale anisotropy in the distribution of space objects and by the torque alignment direction. But since the value of the angular velocity of our Universe is $$\omega_{U_{n}}\sim10^{-19}\;\text{Hz}$$
, finding of such rotation and its influence on the natural processes is extremely difficult. So today dominates the view that the Universe is isotropic, and the cosmological principle is satisfied in it.
TL;DR: In this article, the authors investigated the stability of the universe under linear scalar, vector, and tensor perturbations in the context of a deformed Hoˇrava-Lifshitz cosmology related to entropic forces.
Abstract: We investigate the stability of the Einstein static universe under linear scalar, vector, and tensor perturbations in the context of a deformed Hoˇrava-Lifshitz (HL) cosmology related to entropic forces. We obtain a general stability condition under linear scalar perturbations. Using this general condition, we show that there is no stable Einstein static universe in the case of a flat universe (k = 0). In the special case of large values of the parameter ω of HL gravity in a positively curved universe (k > 0), the domination of the quintessence and phantom matter fields with a barotropic equation of state parameter β −1/3 must be the dominant fields of the universe. We also demonstrate a neutral stability under vector perturbations. We obtain an inequality including the cosmological parameters of the Einstein static universe for stability under tensor perturbations. It turns out that for large values of ω, there is stability under tensor perturbations.