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Showing papers on "Big Rip published in 2016"


Journal ArticleDOI
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.
Abstract: We review the paradigm of holographic dark energy (HDE), which arises from a theoretical attempt of applying the holographic principle (HP) to the dark energy (DE) problem. Making use of the HP and the dimensional analysis, we derive the general formula of the energy density of HDE. Then, we describe the properties of HDE model, in which the future event horizon is chosen as the characteristic length scale. We also introduce the theoretical explorations and the observational constraints for this model. Next, in the framework of HDE, we discuss various topics, such as spatial curvature, neutrino, instability of perturbation, time-varying gravitational constant, inflation, black hole and big rip singularity. In addition, from both the theoretical and the observational aspects, we introduce the interacting holographic dark energy scenario, where the interaction between dark matter and HDE is taken into account. Furthermore, we discuss the HDE scenario in various modified gravity (MG) theories, such as Brans-Dicke theory, braneworld theory, scalar-tensor theory, Horava-Lifshitz theory, and so on. Besides, we introduce the attempts of reconstructing various scalar-field DE and MG models from HDE. Moreover, we introduce other DE models inspired by the HP, in which different characteristic length scales are chosen. Finally, we make comparisons among various HP-inspired DE models, by using cosmological observations and diagnostic tools.

235 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the singularity correspondence between the Jordan and Einstein frames for various F(R) gravity theories, in the absence of any matter fluids, and showed that it is possible to have various correspondences of finite time singularities, and that a singular cosmology in one frame might be non-singular in another frame.

111 citations


Journal ArticleDOI
TL;DR: This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry.
Abstract: While the use of numerical general relativity for modeling astrophysical phenomena and compact objects is commonplace, the application to cosmological scenarios is only just beginning. Here, we examine the expansion of a spacetime using the Baumgarte-Shapiro-Shibata-Nakamura formalism of numerical relativity in synchronous gauge. This work represents the first numerical cosmological study that is fully relativistic, nonlinear, and without symmetry. The universe that emerges exhibits an average Friedmann-Lemaitre-Robertson-Walker (FLRW) behavior; however, this universe also exhibits locally inhomogeneous expansion beyond that expected in linear perturbation theory around a FLRW background.

101 citations



Journal ArticleDOI
TL;DR: In this paper, the authors consider the expansion of the universe powered by the gravitationally induced "adiabatic" matter creation and demonstrate how matter creation works well with the expanding universe.
Abstract: In a flat Friedmann–Lemaitre–Robertson–Walker (FLRW) geometry, we consider the expansion of the universe powered by the gravitationally induced ‘adiabatic’ matter creation. To demonstrate how matter creation works well with the expanding universe, we have considered a general creation rate and analysed this rate in the framework of dynamical analysis. The dynamical analysis hints the presence of a non-singular universe (without the big bang singularity) with two successive accelerated phases, one at the very early phase of the universe (i.e. inflation), and the other one describes the current accelerating universe, where this early, late accelerated phases are associated with an unstable fixed point (i.e. repeller) and a stable fixed point (attractor), respectively. We have described this phenomena by analytic solutions of the Hubble function and the scale factor of the FLRW universe. Using Jacobi last multiplier method, we have found a Lagrangian for this matter creation rate describing this scenario of the universe. To match with our early physics results, we introduce an equivalent dynamics driven by a single scalar field, discuss the associated observable parameters and compare them with the latest Planck data sets. Finally, introducing the teleparallel modified gravity, we have established an equivalent gravitational theory in the framework of matter creation.

60 citations


Journal ArticleDOI
11 Jul 2016-Symmetry
TL;DR: Several observational probes are reviewed—including gravitational lensing, galaxy clusters, cosmic microwave background temperature and polarization, supernova and baryon acoustic oscillations measurements—and their relevance in constraining the cosmological description of the Universe is reviewed.
Abstract: We explore the dynamics and evolution of the Universe at early and late times, focusing on both dark energy and extended gravity models and their astrophysical and cosmological consequences. Modified theories of gravity not only provide an alternative explanation for the recent expansion history of the universe, but they also offer a paradigm fundamentally distinct from the simplest dark energy models of cosmic acceleration. In this review, we perform a detailed theoretical and phenomenological analysis of different modified gravity models and investigate their consistency. We also consider the cosmological implications of well motivated physical models of the early universe with a particular emphasis on inflation and topological defects. Astrophysical and cosmological tests over a wide range of scales, from the solar system to the observable horizon, severely restrict the allowed models of the Universe. Here, we review several observational probes—including gravitational lensing, galaxy clusters, cosmic microwave background temperature and polarization, supernova and baryon acoustic oscillations measurements—and their relevance in constraining our cosmological description of the Universe.

56 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the Joint Light-curve Analysis (JLA) supernova sample to study the acceleration of supernovae in a flat universe and showed that acceleration is quite secure.
Abstract: The accelerating expansion of the universe is one of the most profound discoveries in modern cosmology, pointing to a universe in which 70% of the mass-energy density has an unknown form spread uniformly across the universe This result has been well established using a combination of cosmological probes (eg, Planck Collaboration et al 2016), resulting in a "standard model" of modern cosmology that is a combination of a cosmological constant with cold dark matter and baryons The first compelling evidence for the acceleration came in the late 1990's, when two independent teams studying type Ia supernovae discovered that distant SNe Ia were dimmer than expected The combined analysis of modern cosmology experiments, including SNe Ia, the Hubble constant, baryon acoustic oscillations, and the cosmic microwave background has now measured the contributions of matter and the cosmological constant to the energy density of the universe to better than 001, providing a secure measurement of acceleration A recent study (Trost Nielsen et al 2015) has claimed that the evidence for acceleration from SNe Ia is "marginal" Here we demonstrate errors in that analysis which reduce the acceleration significance from SNe Ia, and further demonstrate that conservative constraints on the curvature or matter density of the universe increase the significance even more Analyzing the Joint Light-curve Analysis supernova sample, we find 42{\sigma} evidence for acceleration with SNe Ia alone, and 112{\sigma} in a flat universe With our improved supernova analysis and by not rejecting all other cosmological constraints, we find that acceleration is quite secure

56 citations


Journal ArticleDOI
02 Jun 2016-Entropy
TL;DR: A general formalism for bulk viscous solutions of the energy-conservation equation for ρ ( a, ζ ) , both for a single-component and a multicomponent fluid in the Friedmann universe is derived, and new insight is brought by using estimates of ζ to analyze the fate of the future universe.
Abstract: We derive a general formalism for bulk viscous solutions of the energy-conservation equation for ρ ( a , ζ ) , both for a single-component and a multicomponent fluid in the Friedmann universe. For our purposes, these general solutions become valuable in estimating the order of magnitude of the phenomenological viscosity in the cosmic fluid at present. H ( z ) observations are found to put an upper limit on the magnitude of the modulus of the present-day bulk viscosity. It is found to be ζ 0 ∼ 10 6 Pa·s, in agreement with previous works. We point out that this magnitude is acceptable from a hydrodynamic point of view. Finally, we bring new insight by using our estimates of ζ to analyze the fate of the future universe. Of special interest is the case ζ ∝ ρ for which the fluid, originally situated in the quintessence region, may slide through the phantom barrier and inevitably be driven into a big rip. Typical rip times are found to be a few hundred Gy.

51 citations


Journal ArticleDOI
TL;DR: In this article, the theoretical and observational consequences of thermodynamics of open systems which allow matter creation, are investigated in modified f(R, T) (R is the Ricci scalar and T is the trace of energy-momentum tensor) theory of gravity within the framework of a flat Friedmann-Robertson-Walker line element.
Abstract: The theoretical and observational consequences of thermodynamics of open systems which allow matter creation, are investigated in modified f(R, T) (R is the Ricci scalar and T is the trace of energy-momentum tensor) theory of gravity within the framework of a flat Friedmann-Robertson-Walker line element. The simplest model f(R, T)=R+2f(T) with “gamma-law” equation of state p = (γ−1)ρ is assumed to obtain the exact solution. A power-law expansion model is proposed by considering the natural phenomenological particle creation rate ψ = 3β n H, where β is a pure number of the order of unity, n the particle number density and H is the Hubble parameter. A Big Rip singularity is observed for γ<0 describing phantom cosmology. The accelerated expansion of the Universe is driven by the particle creation. The density parameter shows the negative curvature of the Universe due to particle creation. The entropy increases with the evolution of the Universe. Some kinematics tests such as lookback time, luminosity distance, proper distance, angular diameter versus redshift are discussed in detail to observe the role of particle creation in early and late time evolution of the Universe.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the initial singularity problem at the quantum level for the closed rainbow cosmology with a homogeneous, isotropic classical space-time background and derived the classical Hamiltonian within the framework of Schutz's formalism for an ideal fluid with a cosmological constant.
Abstract: Using a one-dimensional minisuperspace model with a dimensionless ratio $$\frac{E}{E_{Pl}}$$ , we study the initial singularity problem at the quantum level for the closed rainbow cosmology with a homogeneous, isotropic classical space-time background. We derive the classical Hamiltonian within the framework of Schutz’s formalism for an ideal fluid with a cosmological constant. We characterize the behavior of the system at the early stages of the universe evolution through analyzing the relevant shapes for the potential sector of the classical Hamiltonian for various matter sources, each separately modified by two rainbow functions. We show that for both rainbow universe models presented here, there is the possibility of eliminating the initial singularity by forming a potential barrier and static universe for a non-zero value of the scale factor. We investigate their quantum stability and show that for an energy-dependent space-time geometry with energies comparable with the Planck energy, the non-zero value of the scale factor may be stable. It is shown that under certain constraints the rainbow universe model filled with an exotic matter as a domain wall fluid plus a cosmological constant can result in a non-singular harmonic universe. In addition, we demonstrate that the harmonically oscillating universe with respect to the scale factor is sensitive to $$\frac{E}{E_{Pl}}$$ and that at high energies it may become stable quantum mechanically. Through a Schrodinger–Wheeler–De Witt equation obtained from the quantization of the classical Hamiltonian, we also extract the wave packet of the universe with a focus on the early stages of the evolution. The resulting wave packet supports the existence of a bouncing non-singular universe within the context of gravity’s rainbow proposal.

40 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that such a measurement may be extended to the primordial universe using massive fields as standard clocks, providing a direct evidence for the scenario responsible for the Big Bang.
Abstract: Since Hubble and Lamaitre's discovery of the expanding universe using galaxies till the recent discovery of the accelerating universe using standard candles, direct measurements of the evolution of the scale factor of the universe a(t) have played central roles in establishing the standard model of cosmology. In this letter, we show that such a measurement may be extended to the primordial universe using massive fields as standard clocks, providing a direct evidence for the scenario responsible for the Big Bang. This is a short and non-technical introduction to the idea of classical and quantum primordial standard clocks.

Journal ArticleDOI
TL;DR: In this paper, the effect of the expansion of the universe on the clustering of galaxies is analyzed and the configurational integral for interacting system of galaxies in an expanding universe by including effects produced by the cosmological constant.
Abstract: In this paper, we analyse the effect of the expansion of the universe on the clustering of galaxies. We evaluate the configurational integral for interacting system of galaxies in an expanding universe by including effects produced by the cosmological constant. The gravitational partition function is obtained using this configuration integral. Thermodynamic quantities, specifically, Helmholtz free energy, entropy, internal energy, pressure and chemical potential are also derived for this system. It is observed that they depend on the modified clustering parameter for this system of galaxies. It is also demonstrated that these thermodynamical quantities get corrected because of the cosmological constant.

Journal ArticleDOI
TL;DR: In this article, a model of transitioning universe with minimal interaction between perfect fluid and anisotropic dark energy in Bianchi I space-time is presented, where the two sources are assumed to minimally interacted and therefore their energy momentum tensors are conserved separately.
Abstract: In this paper, we present a model of transitioning universe with minimal interaction between perfect fluid and anisotropic dark energy in Bianchi I space-time. The two sources are assumed to minimally interacted and therefore their energy momentum tensors are conserved separately. The explicit expression for average scale factor are considered in hybrid form that gives time varying deceleration parameter which describes both the early and late time physical features of universe. We also discuss the physical and geometrical properties of the model derived in this paper. The solution is interesting physically as it explain accelerating universe as well as singularity free universe.

Journal ArticleDOI
TL;DR: In this paper, a step-by-step foundation for the differential character of the universe's rotation is presented, invoking the concept of spacetime foam with spin, and it is reasonable to assume that the very early Universe can be described by the Dirac equation.
Abstract: A step-by-step foundation for the differential character of the Universe’s rotation is presented. First, invoking the concept of spacetime foam with spin, it is reasonable to assume that the very early Universe can be described by the Dirac equation. Second, it is shown using the Ehrenfest theorem that, from a classical point of view, the early Universe can be described by the Papapetrou equations. Third, it is stressed that our Universe can perform only rotational motion. It is shown based on the spin part of the Papapetrou equations that the Universe’s rotation depends appreciably on the physical properties of a specific cosmological epoch. The rotational angular velocity is calculated for three basic cosmological epochs: the matter-dominated epoch, the transition period (from domination of matter to domination of vacuum), and the vacuum-dominated epoch.

Journal ArticleDOI
TL;DR: In this article, the Wheeler-DeWitt (WDW) equation is obtained and solved based on an alternative action proposed in ref. [1], under two different factor ordering choices.
Abstract: The quantum effects close to the classical big rip singularity within the Eddington-inspired-Born-Infeld theory (EiBI) are investigated through quantum geometrodynamics. It is the first time that this approach is applied to a modified theory constructed upon Palatini formalism. The Wheeler-DeWitt (WDW) equation is obtained and solved based on an alternative action proposed in ref. [1], under two different factor ordering choices. This action is dynamically equivalent to the original EiBI action while it is free of square root of the spacetime curvature. We consider a homogeneous, isotropic and spatially flat universe, which is assumed to be dominated by a phantom perfect fluid whose equation of state is a constant. We obtain exact solutions of the WDW equation based on some specific conditions. In more general cases, we propose a qualitative argument with the help of a Wentzel-Kramers-Brillouin (WKB) approximation to get further solutions. Besides, we also construct an effective WDW equation by simply promoting the classical Friedmann equations. We find that for all the approaches considered, the DeWitt condition hinting singularity avoidance is satisfied. Therefore the big rip singularity is expected to be avoided through the quantum approach within the EiBI theory.

Journal ArticleDOI
TL;DR: In this article, a new model of nonlinear electromagnetic fields possessing a dimensional parameter $\beta$ is proposed, which is considered as the source of the gravitation field and accelerated expansion of the universe.
Abstract: A new model of nonlinear electromagnetic fields possessing a dimensional parameter $\beta$ is proposed. Electromagnetic fields are considered as the source of the gravitation field and accelerated expansion of the universe is driven by nonlinear electromagnetic fields. We consider the magnetic universe and the stochastic magnetic field is a source of the universe acceleration. After the universe inflation and the accelerated expansion the universe decelerates. We show the causality of the model and a classical stability at the deceleration phase. The spectral index, the tensor-to-scalar ratio, and the running of the spectral index were estimated that approximately fulfil the PLANK, WMAP, and BICEP2 data.

Journal ArticleDOI
TL;DR: In this paper, a model of nonlinear electromagnetic fields with a dimensional parameter $\beta$ was proposed and the bound on the parameter was obtained from the PVLAS experiment and the range of the scale factor, when the causality of the model and a classical stability take place, was obtained.
Abstract: A model of nonlinear electromagnetic fields with a dimensional parameter $\beta$ is proposed. From PVLAS experiment the bound on the parameter $\beta$ was obtained. Electromagnetic fields are coupled with the gravitation field and we show that the universe accelerates due to nonlinear electromagnetic fields. The magnetic universe is considered and the stochastic magnetic field is a background. After inflation the universe decelerates and approaches to the radiation era. The range of the scale factor, when the causality of the model and a classical stability take place, was obtained. The spectral index, the tensor-to-scalar ratio, and the running of the spectral index were estimated which are in approximate agreement with the PLANCK, WMAP, and BICEP2 data.

Journal ArticleDOI
TL;DR: In this paper, a dynamical analysis in the phase space is performed and it is shown that a spatially open universe filled with matter satisfying the strong energy condition can exhibit a stable static phase.
Abstract: We investigate the Einstein static universe (ESU) and the emergent universe scenario in the framework of Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz-like $F(R)$ gravity. We first perform a dynamical analysis in the phase space, and amongst others we show that a spatially open universe filled with matter satisfying the strong energy condition can exhibit a stable static phase. Additionally, we examine the behavior of the scenario under scalar perturbations and extract the conditions under which it is free of perturbative instabilities, showing that the obtained background ESU solutions are free of such instabilities. However, in order for the Einstein static universe to give rise to the emergent universe scenario we need to have an exotic matter sector that can lead the universe to depart from the stable static state and enter into its usual expanding thermal history.

Journal ArticleDOI
TL;DR: In this article, the authors analyzed the behavior of the universe close to a little rip, which can be interpreted as a big rip sent towards the infinite future, and showed that the little rip can be avoided in the sense of the DeWitt criterion, that is, by having a vanishing wave function at the place of the little-rip.
Abstract: We analyze from a classical and quantum point of view the behavior of the universe close to a little rip, which can be interpreted as a big rip sent towards the infinite future. Like a big rip singularity, a little rip implies the destruction of all bounded structure in the Universe and is thus an event where quantum effects could be important. We present here a new phantom scalar field model for the little rip. The quantum analysis is performed in quantum geometrodynamics, with the Wheeler-DeWitt equation as its central equation. We find that the little rip can be avoided in the sense of the DeWitt criterion, that is, by having a vanishing wave function at the place of the little rip. Therefore our analysis completes the answer to the question: can quantum cosmology smoothen or avoid the divergent behavior genuinely caused by phantom matter? We show that this can indeed happen for the little rip, similar to the avoidance of a big rip and a little sibling of the big rip.

Journal ArticleDOI
TL;DR: In this paper, a Gauss-Bonnet modified gravity model with bouncing behavior in the early stages of the universe evolution is presented, in which the equation of state (EoS) parameter, w, is a function of time.
Abstract: The following issue is addressed: How the addition of a Gauss–Bonnet term (generically coming from most fundamental theories, as string and M theories), to a viable model, can change the specific properties, and even the physical nature, of the corresponding cosmological solutions? Specifically, brand new original dark energy models are obtained in this way with quite interesting properties, which exhibit, in a unified fashion, the three distinguished possible cosmological phases corresponding to phantom matter, quintessence and ordinary matter, respectively. A model, in which the equation of state (EoS) parameter, w, is a function of time, is seen to lead either to a singularity of the Big Rip kind or to a bouncing solution which evolves into a de Sitter universe with w = −1. Moreover, new Gauss–Bonnet modified gravity models with bouncing behavior in the early stages of the universe evolution are obtained and tested for the validity and stability of the corresponding solutions. They allow for a remarkably natural, unified description of a bouncing behavior at early times and accelerated expansion at present.

Journal ArticleDOI
TL;DR: In this article, the role of Gauss-Bonnet term for the early and late time accelerating phases of the universe with the help of two viable f(G) models in the background of flat FRW universe model is studied.
Abstract: In this paper, we study the role of Gauss–Bonnet term for the early and late time accelerating phases of the universe with the help of two viable f(G) models in the background of flat FRW universe model. These models show inflationary behavior as well as the present accelerating expansion of the universe. The contribution of Gauss–Bonnet term in pressure and energy density is used to calculate equation of state (EoS) parameter for the modified fluid which behaves like cosmological constant with Ḣ = 0. We discuss early inflation and late accelerating expansion of the universe through scale factor evaluated from equation of continuity numerically.

Journal ArticleDOI
TL;DR: In this article, a simple parametrization of the Hubble parameter H is proposed to explain the late time cosmic acceleration, which can give rise to interesting cosmological phenomena such as big rip singularity, bounce and others.
Abstract: In this paper, we propose a simple parametrization of the Hubble parameter H in order to explain the late time cosmic acceleration. We show that our proposal covers many models obtained in different schemes of parametrization under one umbrella. We demonstrate that a simple modification in the functional form of Hubble parameter can give rise to interesting cosmological phenomena such as big rip singularity, bounce and others. We have also constrained the model parameters using the latest 28 points of H(z) data for three cases which admit transition from deceleration to acceleration.

Journal ArticleDOI
31 Oct 2016-Symmetry
TL;DR: In this review paper, several new results towards the explanation of the accelerated expansion of the large-scale universe is discussed and a new idea, named the varying ghost dark energy, is discussed involving a new concept of dark energy.
Abstract: In this review paper, several new results towards the explanation of the accelerated expansion of the large-scale universe is discussed. On the other hand, inflation is the early-time accelerated era and the universe is symmetric in the sense of accelerated expansion. The accelerated expansion of is one of the long standing problems in modern cosmology, and physics in general. There are several well defined approaches to solve this problem. One of them is an assumption concerning the existence of dark energy in recent universe. It is believed that dark energy is responsible for antigravity, while dark matter has gravitational nature and is responsible, in general, for structure formation. A different approach is an appropriate modification of general relativity including, for instance, f ( R ) and f ( T ) theories of gravity. On the other hand, attempts to build theories of quantum gravity and assumptions about existence of extra dimensions, possible variability of the gravitational constant and the speed of the light (among others), provide interesting modifications of general relativity applicable to problems of modern cosmology, too. In particular, here two groups of cosmological models are discussed. In the first group the problem of the accelerated expansion of large-scale universe is discussed involving a new idea, named the varying ghost dark energy. On the other hand, the second group contains cosmological models addressed to the same problem involving either new parameterizations of the equation of state parameter of dark energy (like varying polytropic gas), or nonlinear interactions between dark energy and dark matter. Moreover, for cosmological models involving varying ghost dark energy, massless particle creation in appropriate radiation dominated universe (when the background dynamics is due to general relativity) is demonstrated as well. Exploring the nature of the accelerated expansion of the large-scale universe involving generalized holographic dark energy model with a specific Nojiri-Odintsov cut-off is presented to finalize the paper.

Journal ArticleDOI
TL;DR: In this paper, the quantum effects close to the classical big rip singularity within the Eddington-inspired Born-Infeld theory are investigated through quantum geometrodynamics.
Abstract: The quantum effects close to the classical big rip singularity within the Eddington-inspired-Born-Infeld theory (EiBI) are investigated through quantum geometrodynamics. It is the first time that this approach is applied to a modified theory constructed upon Palatini formalism. The Wheeler-DeWitt (WDW) equation is obtained and solved based on an alternative action proposed in Ref.[1], under two different factor ordering choices. This action is dynamically equivalent to the original EiBI action while it is free of square root of the spacetime curvature. We consider a homogeneous, isotropic and spatially flat universe, which is assumed to be dominated by a phantom perfect fluid whose equation of state is a constant. We obtain exact solutions of the WDW equation based on some specific conditions. In more general cases, we propose a qualitative argument with the help of a Wentzel-Kramers-Brillouin (WKB) approximation to get further solutions. Besides, we also construct an effective WDW equation by simply promoting the classical Friedmann equations. We find that for all the approaches considered, the DeWitt condition hinting singularity avoidance is satisfied. Therefore the big rip singularity can be avoided through the quantum approach within the EiBI theory.

Journal ArticleDOI
TL;DR: In this paper, the initial forging of elements in the recently proposed Rh = ct universe, a cosmology that demands linear evolution of the scale factor, is considered, and it is shown that the production of helium can be enhanced in such a "simmering universe" by boosting the baryon to photon ratio, although more than an order of magnitude increase is required to bring the helium mass fraction into accordance with observations.
Abstract: Primordial nucleosynthesis is rightly hailed as one of the great successes of the standard cosmological model. Here we consider the initial forging of elements in the recently proposed Rh = ct universe, a cosmology that demands linear evolution of the scale factor. Such a universe cools extremely slowly compared to standard cosmologies, considerably depleting the available neutrons during nucleosynthesis; this has significant implications for the resultant primordial abundances of elements, predicting a minuscule quantity of helium which is profoundly at odds with observations. The production of helium can be enhanced in such a "simmering universe" by boosting the baryon to photon ratio, although more than an order of magnitude increase is required to bring the helium mass fraction into accordance with observations. However, in this scenario, the prolonged period of nucleosynthesis results of the efficient cooking of lighter into heavier elements, impacting the resultant abundances of all elements so that, other than hydrogen and helium, there are virtually no light elements present in the universe. Without the addition of substantial new physics in the early universe, it is difficult to see how the Rh = ct universe can be considered a viable cosmological model.

Journal ArticleDOI
TL;DR: In this article, the authors extend the Einstein-aether theory to take into account the interaction between a pseudoscalar field, which describes the axionic dark matter, and a time-like dynamic unit vector field which characterizes the velocity of the aether motion.
Abstract: We extend the Einstein-aether theory to take into account the interaction between a pseudoscalar field, which describes the axionic dark matter, and a time-like dynamic unit vector field, which characterizes the velocity of the aether motion. The Lagrangian of the Einstein-aether-axion theory includes cross-terms based on the axion field and its gradient four-vector, on the covariant derivative of the aether velocity four-vector, and on the Riemann tensor and its convolutions. We follow the principles of the Effective Field theory, and include into the Lagrangian of interactions all possible terms up to the second order in the covariant derivative. Interpretation of new couplings is given in terms of irreducible parts of the covariant derivative of the aether velocity, namely, the acceleration four-vector, the shear and vorticity tensors, and the expansion scalar. A spatially isotropic and homogeneous cosmological model with dynamic unit vector field and axionic dark matter is considered as an application of the established theory; new exact solutions are discussed, which describe models with a Big Rip, Pseudo Rip and de Sitter-type asymptotic behavior.

Journal ArticleDOI
TL;DR: In this article, the authors investigate the realization of the emergent universe scenario in theories with natural UV cutoffs, namely a minimum length and a maximum momentum, quantified by a new deformation parameter in the generalized uncertainty principle.
Abstract: We investigate the realization of the emergent universe scenario in theories with natural UV cutoffs, namely a minimum length and a maximum momentum, quantified by a new deformation parameter in the generalized uncertainty principle. We extract the Einstein static universe solutions and we examine their stability through a phase-space analysis. As we show, the role of the new deformation parameter is crucial in a twofold way: Firstly, it leads to the appearance of new Einstein static universe critical points, that are absent in standard cosmology. Secondly, it provides a way for a graceful exit from the Einstein static universe into the expanding thermal history, that is needed for a complete and successful realization of the emergent universe scenario.

Posted Content
TL;DR: In this article, the authors used holography for the ab-initio determination of the non-equilibrium behavior of matter in a Friedmann-Lemaitre-Robertson-Walker universe.
Abstract: We use holography for the ab-initio determination of the non-equilibrium behavior of matter in a Friedmann-Lemaitre-Robertson-Walker Universe. We focus on matter without scale invariance and develop an expansion for the corresponding entropy production in terms of the derivatives of the cosmological scale factor. We show that the resulting series is asymptotic and we discuss its resurgent properties. Finally, we compute the resummed entropy production rate in de Sitter Universe at late times and show that the leading order approximation given by bulk viscosity effects can strongly overestimate/underestimate the rate depending on the microscopic parameters.

Journal ArticleDOI
TL;DR: In this paper, results on particle creation from vacuum by the gravitational field of the expanding Friedmann Universe are presented. But the results for the density of particles and the energy density for created particles are given for different exact solutions and different expansion modes of the universe.
Abstract: Results on particle creation from vacuum by the gravitational field of the expanding Friedmann Universe are presented. Finite results for the density of particles and the energy density for created particles are given for different exact solutions and different expansion modes of the Universe. The results are obtained for both conformal and nonconformal particles. The hypothesis on the origin of visible matter from the decay of created from vacuum superheavy particles identified with dark matter is discussed.

Journal ArticleDOI
TL;DR: In this article, the cosmological consequences of interacting dark energy (IDE) models using the SNLS3 supernova samples were explored using three IDE models: SALT2, SiFTO and combined sample.
Abstract: We explore the cosmological consequences of interacting dark energy (IDE) models using the SNLS3 supernova samples. In particular, we focus on the impacts of different SNLS3 light-curve fitters (LCF; referred to in this paper as SALT2, SiFTO and combined sample). Firstly, making use of the three SNLS3 data sets, as well as the Planck distance priors data and the galaxy clustering data, we constrain the parameter spaces of three IDE models. Then, we study the cosmic evolutions of Hubble parameter H (z ), deceleration diagram q (z ), statefinder hierarchy S(1) 3 (z) and S(1) 4 (z) , and check whether or not these dark energy diagnosis can distinguish the differences among the results of different SNLS3 LCF. Finally, we perform a high redshift cosmic age test using three old high redshift objects (OHRO), and explore the fate of the Universe. We find that the impacts of different SNLS3 LCF are rather small, and can not be distinguished using H (z ), q (z ), S(1) 3 (z) , S(1) 4 (z) , and the age data of OHRO. In addition, we infer, from the current observations, how far we are from a cosmic doomsday in the worst case, and find that the combined sample always gives the largest 2σ lower limit of the time interval between “big rip” and today, while the results given by the SALT2 and the SiFTO sample are similar. These conclusions are insensitive to a specific form of dark sector interaction. Our method can be used to distinguish the differences among various cosmological observations.