Showing papers on "Particle horizon published in 2011"
TL;DR: In this article, the authors proposed an alternative interpretation which takes into account the entropy and temperature intrinsic to the horizon of the universe due to the information holographically stored there, and showed that this leads to the entropic accelerating universe.
226 citations
TL;DR: In this paper, a detailed phase-space analysis of the universe is performed, and it is shown that at late times the universe can result in a state of accelerating expansion, and additionally, for a particular n-range (2 < n < 3), it exhibits phantom behavior.
Abstract: We construct general anisotropic cosmological scenarios governed by an f(R) gravitational sector. Focusing then on Kantowski–Sachs geometries in the case of Rn-gravity, and modeling the matter content as a perfect fluid, we perform a detailed phase-space analysis. We find that at late times the universe can result in a state of accelerating expansion, and additionally, for a particular n-range (2 < n < 3), it exhibits phantom behavior. Furthermore, isotropization has been achieved independently of the initial anisotropy degree, showing in a natural way why the observable universe is so homogeneous and isotropic, without relying on a cosmic no-hair theorem. Moreover, contracting solutions also have a large probability to be the late-time states of the universe. Finally, we can also obtain the realization of the cosmological bounce and turnaround, as well as of cyclic cosmology. These features indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios.
105 citations
TL;DR: In this article, a generic type of signals that exist in primordial universe models can be used for experimentally distinguishing different universe paradigms that lead to the Big Bang model.
95 citations
TL;DR: In this paper, the authors determined the peculiar velocity of the solar system relative to the frame of distant radio sources, by studying the anisotropy in the sky brightness from discrete radio sources.
Abstract: According to the cosmological principle, the Universe should appear isotropic, without any preferred directions, to an observer whom we may consider to be fixed in the co-moving co-ordinate system of the expanding Universe. Such an observer is stationary with respect to the average distribution of the matter in the Universe and the sky brightness at any frequency should appear uniform in all directions to such an observer. However a peculiar motion of such an observer, due to a combined effect of Doppler boosting and aberration, will introduce a dipole anisotropy in the observed sky brightness; in reverse an observed dipole anisotropy in the sky brightness could be used to infer the peculiar velocity of the observer with respect to the average Universe. We determine the peculiar velocity of the solar system relative to the frame of distant radio sources, by studying the anisotropy in the sky brightness from discrete radio sources, i.e., an integrated emission from discrete sources per unit solid angle. Our results give a direction of the velocity vector in agreement with the Cosmic Microwave Background Radiation (CMBR) value, but the magnitude ($\sim 1600\pm 400$ km/s) is $\sim 4$ times the CMBR value ($369\pm 1$ km/s) at a statistically significant ($\sim 3\sigma$) level. A genuine difference between the two dipoles would imply anisotropic Universe, with the anisotropy changing with the epoch. This would violate the cosmological principle where the isotropy of the Universe is assumed for all epochs, and on which the whole modern cosmology is based upon.
88 citations
TL;DR: In this article, the authors reexamine the primordial non-Gaussianity in single field models, focusing on the bispectrum in the squeezed limit, and show that if we adopt a genuine gauge invariant variable which is naturally composed purely of the information in our local observable universe, the leading term for the Bispectrum predicted by the consistency relation vanishes.
Abstract: The conventional cosmological perturbation theory has been performed under the assumption that we know the whole spatial region of the universe with infinite volume. This is, however, not the case in the actual observations because observable portion of the universe is limited. To give a theoretical prediction to the observable fluctuations, gauge-invariant observables should be composed of the information in our local observable universe with finite volume. From this point of view, we reexamine the primordial non-Gaussianity in single field models, focusing on the bispectrum in the squeezed limit. A conventional prediction states that the bispectrum in this limit is related to the power spectrum through the so-called consistency relation. However, it turns out that, if we adopt a genuine gauge invariant variable which is naturally composed purely of the information in our local universe, the leading term for the bispectrum in the squeezed limit predicted by the consistency relation vanishes.
84 citations
TL;DR: The Horizon Run 2 (HR2) and Horizon Run 3 (HR3) simulations as discussed by the authors have been used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science.
Abstract: We present two large cosmological N-body simulations, called Horizon Run 2 (HR2) and Horizon Run 3 (HR3), made using 6000^3 = 216 billions and 7210^3 = 374 billion particles, spanning a volume of (7.200 Gpc/h)^3 and (10.815 Gpc/h)^3, respectively. These simulations improve on our previous Horizon Run 1 (HR1) up to a factor of 4.4 in volume, and range from 2600 to over 8800 times the volume of the Millennium Run. In addition, they achieve a considerably finer mass resolution, down to 1.25x10^11 M_sun/h, allowing to resolve galaxy-size halos with mean particle separations of 1.2 Mpc/h and 1.5 Mpc/h, respectively. We have measured the power spectrum, correlation function, mass function and basic halo properties with percent level accuracy, and verified that they correctly reproduce the LCDM theoretical expectations, in excellent agreement with linear perturbation theory. Our unprecedentedly large-volume N-body simulations can be used for a variety of studies in cosmology and astrophysics, ranging from large-scale structure topology, baryon acoustic oscillations, dark energy and the characterization of the expansion history of the Universe, till galaxy formation science - in connection with the new SDSS-III. To this end, we made a total of 35 all-sky mock surveys along the past light cone out to z=0.7 (8 from the HR2 and 27 from the HR3), to simulate the BOSS geometry. The simulations and mock surveys are already publicly available at this http URL
82 citations
TL;DR: It is shown that one can use the no-boundary wave function to calculate small departures from homogeneity within the authors' past light cone despite the possibility of much larger fluctuations on super horizon scales.
Abstract: We consider landscape models that admit several regions where the conditions for eternal inflation hold. It is shown that one can use the no-boundary wave function to calculate small departures from homogeneity within our past light cone despite the possibility of much larger fluctuations on super horizon scales. The dominant contribution comes from the history exiting eternal inflation at the lowest value of the potential. In a class of landscape models this predicts a tensor to scalar ratio of about 10%. In this way the no-boundary wave function defines a measure for the prediction of local cosmological observations.
65 citations
TL;DR: In this article, the authors examined the evolution of a universe comprising two fluids which interact via a term proportional to the product of their densities and showed that the ratio of the densities tends to a constant after an initial cooling-off period.
Abstract: We examine the evolution of a universe comprising two fluids which interact via a term proportional to the product of their densities. In the case of two matter fluids, it is shown that the ratio of the densities tends to a constant after an initial cooling-off period. We then obtain a complete solution for the cosmological constant ($w=\ensuremath{-}1$) scenario and show that periodic solutions can occur if $wl\ensuremath{-}1$. We further demonstrate that the ratio of the dark matter and dark energy densities is confined to a bounded interval and that this ratio can be $O(1)$ at infinitely many times in the history of the universe, thus solving the coincidence problem. Finally, we show that, for a certain choice of parameters, the model is a viable fit to observational constraints, and we give a detailed discussion of the past and future evolution of the universe in this particular case.
48 citations
TL;DR: In this article, the authors show that the characteristics of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities.
Abstract: Inflation provides a natural mechanism to account for the origin of cosmic structures. The generation of primordial inhomogeneities during inflation can be understood via the spontaneous creation of quanta from the vacuum. We show that when the corresponding {\it stimulated} creation of quanta is considered, the characteristics of the state of the universe at the onset of inflation are not diluted by the inflationary expansion and can be imprinted in the spectrum of primordial inhomogeneities. The non-gaussianities (particularly in the so-called squeezed configuration) in the cosmic microwave background and galaxy distribution can then tell us about the state of the universe that existed at the time when quantum field theory in curved spacetime first emerged as a plausible effective theory.
46 citations
TL;DR: In this article, the curvature scale of the universe is conservatively constrained to be Rc > 42 Gpc (99 per cent), corresponding to a lower limit to the number of Hubble spheres in the Universe NU > 251 (99 percent).
Abstract: Bayesian model averaging is a procedure to obtain parameter constraints that account for the uncertainty about the correct cosmological model. We use recent cosmological observations and Bayesian model averaging to derive tight limits on the curvature parameter, as well as robust lower bounds on the curvature radius of the Universe and its minimum size, while allowing for the possibility of an evolving dark energy component. Because flat models are favoured by Bayesian model selection, we find that model-averaged constraints on the curvature and size of the Universe can be considerably stronger than non-model-averaged ones. For the most conservative prior choice (based on inflationary considerations), our procedure improves on non-model-averaged constraints on the curvature by a factor of ∼2. The curvature scale of the Universe is conservatively constrained to be Rc > 42 Gpc (99 per cent), corresponding to a lower limit to the number of Hubble spheres in the Universe NU > 251 (99 per cent).
41 citations
TL;DR: In this paper, the authors present exact solutions which presumably describe black holes in the background of a spatially flat, pressureless dark-matter, or dark matter plus dark energy, or quintom-dominated universe.
Abstract: We present new exact solutions which presumably describe black holes in the background of a spatially flat, pressureless dark-matter-- or dark matter plus dark energy ($\mathrm{DM}+\mathrm{DE}$)- or quintom-dominated Universe. These solutions generalize Lema\^{\i}tre-Tolman-Bondi metrics. For a dark-matter-- or ($\mathrm{DM}+\mathrm{DE}$)-dominated universe, the area of the black hole apparent horizon (AH) decreases with the expansion of the Universe while that of the cosmic AH increases. However, for a quintom-dominated universe, the black hole AH first shrinks and then expands, while the cosmic AH first expands and then shrinks. A ($\mathrm{DM}+\mathrm{DE}$)-dominated universe containing a black hole will evolve to the Schwarzschild-de Sitter solution with both AHs approaching constant size. In a quintom-dominated universe, the black hole and cosmic AHs will coincide at a certain time, after which the singularity becomes naked, violating cosmic censorship.
TL;DR: In this article, the behavior of accelerating universe is investigated for three purely kinetic k-essence models, and it is found that all these models exhibit quintessence behavior of the universe.
Abstract: The generalized teleparallel gravity has been suggested to explain the present cosmic acceleration of the universe. In this paper, we take spatially homogenous and anisotropic Bianchi type $I$ universe in the framework of $F(T)$ gravity. The behavior of accelerating universe is investigated for three purely kinetic k-essence models. We explore equation of state parameter and deceleration parameter for these k-essence models. It is found that all these models exhibit quintessence behavior of the universe.
TL;DR: In this paper, the authors present new measurements of the coherent motion of galaxies based on observations of the large-scale redshift-space distortions seen in the two-dimensional two-point correlation function of Luminous Red Galaxies in Data Release Seven of the Sloan Digital Sky Survey.
Abstract: We present new measurements of the coherent motion of galaxies based on observations of the large-scale redshift-space distortions seen in the two-dimensional two-point correlation function of Luminous Red Galaxies in Data Release Seven of the Sloan Digital Sky Survey. We have developed a new methodology for estimating these coherent motions, which is less dependent on the details of galaxy bias and of the cosmological model to explain the late-time acceleration of the expansion of the Universe. We measure a one-dimensional velocity dispersion of galaxies on large-scales of σv = h-1 Mpc and σv = h-1 Mpc at a mean redshift of z = 0.25 and 0.38 respectively. These values are fully consistent with predictions for a WMAP7-normalised ΛCDM Universe and inconsistent at confidence of 3.8σ with a Dvali-Gabadadze-Porrati (DGP) model for the Universe. We can convert the units of these σv measurements to km/s and km/s respectively (assuming a ΛCDM universe), which are lower that expected based on recent low redshift (z < 0.2) measurements of the peculiar velocity field (or "bulk flows"). It is difficult to directly compare these measurements as they cover different redshift ranges and different areas of the sky. However, one possible cosmological explanation for this discrepancy is that our Galaxy is located in unusually over, or under, dense region of the Universe.
TL;DR: In this paper, the authors investigated the time varying Λ ( t ) corresponding to the length scales, including the Hubble horizon, the particle horizon and the future event horizon, and the time scales including the age of the universe and the conformal time.
TL;DR: In this paper, the authors studied the effect of cosmic parallax within the "ellipsoidal universe" model, namely a particular homogeneous anisotropic cosmological model of Bianchi type I, whose attractive feature is the potentiality to account for the observed lack of power of the large-scale cosmic microwave background anisotropy.
Abstract: The detection of a time variation of the angle between two distant sources would reveal an anisotropic expansion of the Universe. We study this effect of "cosmic parallax" within the "ellipsoidal universe" model, namely a particular homogeneous anisotropic cosmological model of Bianchi type I, whose attractive feature is the potentiality to account for the observed lack of power of the large-scale cosmic microwave background anisotropy. The preferred direction in the sky, singled out by the axis of symmetry inherent to planar symmetry of ellipsoidal universe, could in principle be constrained by future cosmic parallax data. However, that will be a real possibility if and when the experimental accuracy will be enhanced at least by two orders of magnitude.
TL;DR: In this paper, the authors studied the early evolution of the universe with particle creation in the framework of the flat Friedmann-Robertson-Walker line element and derived exact expressions for the lookback time, proper distance, luminosity distance and angular diameter distance versus redshift.
Abstract: We study some properties of the early evolution of the universe with particle creation in the framework of the flat Friedmann-Robertson-Walker line element. The field equations are solved by using “gamma-law” equation of state p=(γ−1)ρ, where the parameter γ varies with cosmological time. A unified description of the early evolution of the universe is presented in which an inflationary phase is followed by a radiation-dominated phase. Exact expressions for the lookback time, proper distance, luminosity distance and angular diameter distance versus redshift are derived and their meaning discussed in detail. It is found that the negative pressure due to the particle creation may play the role of an accelerating universe.
TL;DR: In this article, the authors considered the magnetic universe in non-linear electrodynamics and discussed the validity of the generalized second law of thermodynamics of magnetic universe bounded by Hubble, apparent, particle and event horizons.
TL;DR: In this paper, a set of locally averaged cosmological parameters in the context of the flat Lambda cold dark matter model was determined using the Buchert averaging formalism.
Abstract: Modern cosmology relies on the assumption of large-scale isotropy and homogeneity of the Universe. However, locally the Universe is inhomogeneous and anisotropic. So, how can local measurements (at the 100 Mpc scale) be used to determine global cosmological parameters (defined at the 10 Gpc scale)? We use Buchert's averaging formalism and determine a set of locally averaged cosmological parameters in the context of the flat Lambda cold dark matter model. We calculate their ensemble means (i.e. their global values) and variances (i.e. their cosmic variances). We apply our results to typical survey geometries and focus on the study of the effects of local fluctuations of the curvature parameter. By this means we show, that in the linear regime cosmological backreaction and averaging can be reformulated as the issue of cosmic variance. The cosmic variance is found largest for the curvature parameter and discuss some of its consequences. We further propose to use the observed variance of cosmological parameters to measure the growth factor. [abbreviated]
TL;DR: In this paper, a new model of the Archimedean-type interaction between dark matter and dark energy is presented, based on the results of numerical and qualitative analysis, and the universe expansion is shown to be perpetually accelerated, periodic or quasiperiodic with a finite number of deceleration/acceleration epochs.
Abstract: In this (second) part of the work we present the results of numerical and qualitative analysis, based on a new model of the Archimedean-type interaction between dark matter and dark energy. The Archimedean-type force is linear in the four-gradient of the dark energy pressure and plays a role of self-regulator of the energy redistribution in a cosmic dark fluid. Because of the Archimedean-type interaction the cosmological evolution is shown to have a multistage character. Depending on the choice of the values of the model-guiding parameters, the Universe expansion is shown to be perpetually accelerated, periodic or quasiperiodic with a finite number of deceleration/acceleration epochs. We distinguished the models, which can be definitely characterized by the inflation in the early Universe, by the late-time accelerated expansion and nonsingular behavior in intermediate epochs, and classified them with respect to a number of transition points. Transition points appear, when the acceleration parameter changes the sign, providing the natural partition of the Universe's history into epochs of accelerated and decelerated expansion. The strategy and results of numerical calculations are advocated by the qualitative analysis of the instantaneous phase portraits of the dynamic system associated with the key equation for the dark energy pressure evolution.
TL;DR: In this article, a non-singular origin for the universe starting from an Einstein static universe, the so called "emergent universe" scenario, in the framework of a theory which uses two volume elements, i.e., curvature, curvature square terms and for scale invariance a dilaton field $\phi$ are considered in the action.
Abstract: We consider a non singular origin for the Universe starting from an Einstein static Universe, the so called "emergent universe" scenario, in the framework of a theory which uses two volume elements $\sqrt{-{g}}d^{4}x$ and $\Phi d^{4}x$, where $\Phi $ is a metric independent density, used as an additional measure of integration. Also curvature, curvature square terms and for scale invariance a dilaton field $\phi$ are considered in the action. The first order formalism is applied. The integration of the equations of motion associated with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of scale invariance (S.I.). After S.S.B. of S.I., it is found that a non trivial potential for the dilaton is generated. In the Einstein frame we also add a cosmological term that parametrizes the zero point fluctuations. The resulting effective potential for the dilaton contains two flat regions, for $\phi \rightarrow \infty$ relevant for the non singular origin of the Universe, followed by an inflationary phase and $\phi \rightarrow -\infty$, describing our present Universe. The dynamics of the scalar field becomes non linear and these non linearities are instrumental in the stability of some of the emergent universe solutions, which exists for a parameter range of values of the vacuum energy in $\phi \rightarrow -\infty$, which must be positive but not very big, avoiding the extreme fine tuning required to keep the vacuum energy density of the present universe small. Zero vacuum energy density for the present universe defines the threshold for the creation of the universe.
TL;DR: In this article, the authors considered that the flat FRW universe is filled with the mixture of dark matter and the new holographic dark energy and examined the validity of the first and generalized second laws of thermodynamics under these interactions on the event as well as apparent horizon.
Abstract: In this work, we have considered that the flat FRW universe is filled with the mixture of dark matter and the new holographic dark energy If there is an interaction, we have investigated the natures of deceleration parameter, statefinder and $Om$ diagnostics We have examined the validity of the first and generalized second laws of thermodynamics under these interactions on the event as well as apparent horizon It has been observed that the first law is violated on the event horizon However, the generalized second law is valid throughout the evolution of the universe enveloped by the apparent horizon When the event horizon is considered as the enveloping horizon, the generalized second law is found to break down excepting at late stage of the universe
TL;DR: In this article, the authors present the results of their confrontation of one example class of SFS models with the available cosmological data from high redshift supernovae, baryon acoustic oscillations (BAO) and the cosmic microwave background (CMB).
Abstract: Current observational evidence does not yet exclude the possibility that dark energy could be in the form of phantom energy. A universe consisting of a phantom constituent will be driven toward a drastic end known as the `Big Rip' singularity where all the matter in the universe will be destroyed. Motivated by this possibility, other evolutionary scenarios have been explored by Barrow, including the phenomena which he called Sudden Future Singularities (SFS). In such a model it is possible to have a blow up of the pressure occurring at sometime in the future evolution of the universe while the energy density would remain unaffected. The particular evolution of the scale factor of the universe in this model that results in a singular behaviour of the pressure also admits acceleration in the current era. In this paper we will present the results of our confrontation of one example class of SFS models with the available cosmological data from high redshift supernovae, baryon acoustic oscillations (BAO) and the cosmic microwave background (CMB). We then discuss the viability of the model in question as an alternative to dark energy.
TL;DR: In this article, a vacuum Bianchi IX universe was studied in the context of the Friedmann-Lemaitre-Robertson-Walker spacetime, and the authors analyzed how anisotropy changes the history of the universe.
Abstract: We study a vacuum Bianchi IX universe in the context of Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz gravity. In particular, we focus on the classical dynamics of the universe and analyze how anisotropy changes the history of the universe. For small anisotropy, we find an oscillating universe as well as a bounce universe just as the case of the Friedmann-Lemaitre-Robertson-Walker spacetime. However, if the initial anisotropy is large, we find the universe which ends up with a big crunch after oscillations if a cosmological constant $\ensuremath{\Lambda}$ is zero or negative. For $\ensuremath{\Lambda}g0$, we find a variety of histories of the universe, that is a de Sitter expanding universe after oscillations in addition to the oscillating solution and the previous big crunch solution. This fate of the universe shows sensitive dependence of initial conditions, which is one of the typical properties of a chaotic system. If the initial anisotropy is near the upper bound, we find the universe starting from a big bang and ending up with a big crunch for $\ensuremath{\Lambda}\ensuremath{\le}0$, and a de Sitter expanding universe starting from a big bang for $\ensuremath{\Lambda}g0$.
TL;DR: In this article, the authors investigated the validity of the generalized second law of thermodynamics in logamediate and intermediate scenarios of the universe bounded by the Hubble, apparent, particle and event horizons using and without using first law.
Abstract: In this work, we have investigated the validity of the generalized second law of thermodynamics in logamediate and intermediate scenarios of the universe bounded by the Hubble, apparent, particle and event horizons using and without using first law of thermodynamics. We have observed that the GSL is valid for Hubble, apparent, particle and event horizons of the universe in the logamediate scenario of the universe using first law and without using first law. Similarly the GSL is valid for all horizons in the intermediate scenario of the universe using first law. Also in the intermediate scenario of the universe, the GSL is valid for Hubble, apparent and particle horizons but it breaks down whenever we consider the universe enveloped by the event horizon.
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TL;DR: An informal description of the Cyclic Inflation scenario which allows the universe to "start" with a negative potential energy, inflate, and then gracefully exit to a positive potential energy universe is presented.
Abstract: In this paper we present an informal description of the Cyclic Inflation scenario which allows our universe to "start" with a negative potential energy, inflate, and then gracefully exit to a positive potential energy universe. We discuss how this scenario fares in comparison with the standard inflationary paradigm with respect to the classic cosmological puzzles associated with the horizon, flatness and isotropy of our current universe. We also discuss some of the most debilitating problems of cyclic cosmologies, Tolman's entropy problem, and the problem with the overproduction of blackholes. We also sketch the calculation of the primordial spectrum in these models and possible observable signatures. We end with a special focus on the exit mechanism where the universe can transition from the negative to a positive potential region. The treatise is based on an ongoing collaboration between the authors and closely follows conference presentations given on the subject by TB.
TL;DR: In this article, it was shown that there is a corresponding Hawking radiation from the cosmological horizon of the de Sitter spacetime, and that the deSitter spacetimes can be a special case of a FRW universe.
TL;DR: In this paper, the authors explore the possibility that the dynamics of the universe can be reproduced choosing appropriately the initial global topology of the Universe, and they start with two concentric spherical three-dimensional branes S 3, with radius a1 < a2 immersed in a five-dimensional space-time.
Abstract: We explore the possibility that the dynamics of the universe can be reproduced choosing appropriately the initial global topology of the Universe. In this work we start with two concentric spherical three-dimensional branes S 3 , with radius a1 < a2 immersed in a five-dimensional space-time. The novel feature of this model is that in the interior brane there exist only spin-zero fundamental fields (scalarfields), while in the exterior one there exist only spin-one fundamental interactions. As usual, the bulk of the universe is dominated by gravitational interactions. In this model, like in the Ekpyrotic one, the Big Bang is consequence of the collision of the branes and causes the existence of the particles predicted by the standard model in the exterior brane (our universe). The scalar fields on the interior brane interact with the spin-one fields on the exterior one only through gravitation, they induce the effect of Scalar Field Dark Matter with an ultra-light mass on the exterior one. We discuss two dif- ferent regimes where the energy density and the brane tension are compared, with the aim to obtain the observed dynamics of the universe after the collision of the branes.
TL;DR: In this paper, a conformal field theory minimally coupled to gravity is proposed to predict a scale invariant spectrum of perturbations in the very early universe, which is very similar to our model.
Abstract: We present a novel theory of the very early universe which addresses the traditional horizon and flatness problems of big bang cosmology and predicts a scale invariant spectrum of perturbations. Unlike inflation, this scenario requires no exponential accelerated expansion of space-time. Instead, the early universe is described by a conformal field theory minimally coupled to gravity. The conformal fields develop a time-dependent expectation value which breaks the flat space so(4,2) conformal symmetry down to so(4,1), the symmetries of de Sitter, giving perturbations a scale invariant spectrum. The solution is an attractor, at least in the case of a single time-dependent field. Meanwhile, the metric background remains approximately flat but slowly contracts, which makes the universe increasingly flat, homogeneous and isotropic, akin to the smoothing mechanism of ekpyrotic cosmology. Our scenario is very general, requiring only a conformal field theory capable of developing the appropriate time-dependent expectation values, and encompasses existing incarnations of this idea, specifically the U(1) model of Rubakov and the Galileon Genesis scenario. Its essential features depend only on the symmetry breaking pattern and not on the details of the underlying lagrangian. It makes generic observational predictions that make it potentially distinguishable from standard inflation, in particular significant non-gaussianities and the absence of primordial gravitational waves.
TL;DR: In this paper, the authors deduce general expressions for the line element of universe models with positive spatial curvature described by conformally flat-spacetime coordinates, and show that there is continual annihilation of space, matter and energy in a dust and radiation-dominated universe, and continual creation in a Lorentz Invariant Vacuum Energy (LIVE)-dominated universe when conformal time is used in Friedmann-Robertson-Walker (FRW) models.
Abstract: We deduce general expressions for the line element of universe models with positive spatial curvature described by conformally flat-spacetime coordinates. Models with dust, radiation and vacuum energy are exhibited. Discussing the existence of particle horizons we show that there is continual annihilation of space, matter and energy in a dust- and radiation-dominated universe, and continual creation in a Lorentz Invariant Vacuum Energy (LIVE)-dominated universe when conformal time is used in Friedmann-Robertson-Walker (FRW) models with positive spatial curvature. A general procedure is given for finding coordinates to be used in Penrose diagrams. We also calculate the age and the redshift of some universe models using conformal time.
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TL;DR: In this article, a general solution for a single fluid in which the speed of sound vanishes was proposed. But this solution is not compatible with current observational data and cannot explain the acceleration of the universe.
Abstract: Assuming that the Universe is filled by one single fluid, we present in the context of General Relativity a possible explanation for the acceleration of the Universe. We use ordinary thermodynamics and the fact that small matter perturbations barely propagate in our Universe, to derive a general solution for a single fluid in which the speed of sound vanishes. We find a model that contains $\Lambda$CDM as a special case, and is compatible with current observational data.