Showing papers on "Particle horizon published in 2012"
TL;DR: In this paper, the cosmological reconstruction in an anisotropic universe for both the homogeneous and inhomogeneous content of the universe is investigated for Bianchi types I, Bianchi type III, and Kantowski-Sachs models.
Abstract: We investigate the cosmological reconstruction in an anisotropic universe for both the homogeneous and inhomogeneous content of the universe Special attention is given to three interesting cases: Bianchi type I, Bianchi type III, and Kantowski-Sachs models The de Sitter, power-law, and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed Moreover, for the general exponential solutions---from which the de Sitter and power-law solutions may be obtained---we obtain models which reproduce the early Universe (assuming inflation) and the late-time accelerated expanding Universe The models obtained for the late-time Universe are consistent with a known result in the literature where a power-law type correction in $T$ is added to a power-law type of $f(T)$ for guaranteeing the avoidance of the big rip and the big freeze
134 citations
TL;DR: The Dirac-Milne universe, a matter-antimatter symmetric cosmology, was studied in this paper, where antimatter is supposed to present a negative active gravitational mass.
Abstract: The ΛCDM standard model, although an excellent parametrization of the present cosmological data, contains two as yet unobserved components, dark matter and dark energy, that constitute more than 95% of the Universe. Faced with this unsatisfactory situation, we study an unconventional cosmology, the Dirac-Milne universe, a matter-antimatter symmetric cosmology, in which antimatter is supposed to present a negative active gravitational mass. The main feature of this cosmology is the linear evolution of the scale factor with time, which directly solves the age and horizon problems of a matter-dominated universe. We study the concordance of this model to the cosmological test of type Ia supernovae distance measurements and calculate the theoretical primordial abundances of light elements for this cosmology. We also show that the acoustic scale of the cosmic microwave background naturally emerges at the degree scale despite an open geometry.
97 citations
TL;DR: In this paper, the authors proposed an alternative, nonsingular, cosmic scenario based on gravitationally induced particle production, which is an attempt to evade the coincidence and cosmological constant problems of the standard model and also to connect the early and late time accelerating stages of the universe.
Abstract: We propose an alternative, nonsingular, cosmic scenario based on gravitationally induced particle production. The model is an attempt to evade the coincidence and cosmological constant problems of the standard model (�CDM) and also to connect the early and late time accelerating stages of the Universe. Our space-time emerges from a pure initial de Sitter stage thereby providing a natural solution to the horizon problem. Subsequently, due to an instability provoked by the production of massless particles, the Universe evolves smoothly to the standard radiation dominated era thereby ending the production of radiation as required by the conformal invariance. Next, the radiation becomes subdominant with the Universe entering in the cold dark matter dominated era. Finally, the negative pressure associated with the creation of cold dark matter (CCDM model) particles accelerates the expansion and drives the Universe to a final de Sitter stage. The late time cosmic
85 citations
TL;DR: In this paper, it was shown that the horizon problem in the standard model of cosmology arises from the observed uniformity of the cosmic microwave background radiation, which has the same temperature everywhere (except for tiny, stochastic fluctuations), even in regions on opposite sides of the sky, which appear to lie outside of each other's causal horizon.
Abstract: The horizon problem in the standard model of cosmology (LDCM) arises from the observed uniformity of the cosmic microwave background radiation, which has the same temperature everywhere (except for tiny, stochastic fluctuations), even in regions on opposite sides of the sky, which appear to lie outside of each other's causal horizon. Since no physical process propagating at or below lightspeed could have brought them into thermal equilibrium, it appears that the universe in its infancy required highly improbable initial conditions. In this paper, we examine this well-known problem by considering photon propagation through a Friedmann-Robertson-Walker (FRW) spacetime at a more fundamental level than has been attempted before, demonstrating that the horizon problem only emerges for a subset of FRW cosmologies, such as LCDM, that include an early phase of rapid deceleration. We show that the horizon problem is nonexistent for the recently introduced R_h=ct universe, obviating the principal motivation for the inclusion of inflation. We demonstrate through direct calculation that, in the R_h=ct universe, even opposite sides of the cosmos have remained causally connected to us - and to each other - from the very first moments in the universe's expansion. Therefore, within the context of the R_h=ct universe, the hypothesized inflationary epoch from t=10^{-35} seconds to 10^{-32} seconds was not needed to fix this particular "problem", though it may still provide benefits to cosmology for other reasons.
81 citations
TL;DR: In this paper, the authors derive several families of accelerating universe solutions to an Einstein-Aether gravity theory, which provide possible descriptions of inflationary behavior in the early universe and late-time cosmological acceleration.
Abstract: We show how to derive several families of accelerating universe solutions to an Einstein-Aether gravity theory. These solutions provide possible descriptions of inflationary behavior in the early universe and late-time cosmological acceleration.
77 citations
TL;DR: The behavior of the apparent (black hole and cosmological) horizons of the McVittie spacetime is discussed in this paper using an analogy to the Schwarzschild-de Sitter-Kottler spacetime.
Abstract: The bizarre behavior of the apparent (black hole and cosmological) horizons of the McVittie spacetime is discussed using, as an analogy, the Schwarzschild-de Sitter-Kottler spacetime (which is a special case of McVittie anyway). For a dust-dominated ``background'' universe, a black hole cannot exist at early times because its (apparent) horizon would be larger than the cosmological (apparent) horizon. A phantom-dominated background universe causes this situation, and the horizon behavior, to be time-reversed.
58 citations
TL;DR: In this article, the cosmological quark-hadron phase transition in two different physical scenarios is studied, assuming that the phase transition would be described by an effective nucleation theory (prompt first-order phase transition).
Abstract: In the standard hot big bang theory, when the Universe was about 1 10 �s old, the cosmological matter is conjectured to undergo Quantum Chromodynamics (QCD) phase transition(s) from quark matter to hadrons. In the present work, we study the cosmological quark-hadron phase transition in two different physical scenarios. First, by assuming that the phase transition would be described by an effective nucleation theory (prompt first-order phase transition), we analyze the evolution of the relevant cosmological parameters of the early Universe (energy density ρ, temperature T, Hubble parameter H and the scale factor a) before, during and after the phase transition. To study the cosmological dynamics and the time evolution, we use both analytical and numerical methods. The case where the Universe evolved through a mixed phase with a small initial supercooling and monotonically growing hadronic bubbles is also considered in detail. The numerical estimation of the cosmological parameters, a and H for instance, shows that the time evolution of the Universe varies from phase to phase. As the QCD era turns to be fairly accessible in the high-energy experiments and the lattice QCD simulations, the QCD equation of state is very well defined. In light of these QCD results, we develop a systematic study of the crossover quark-hadron phase transition and an estimation for the time evolution of the Hubble parameter during the crossover .
53 citations
TL;DR: In this paper, the authors focus on the possible absence of angular correlation in the CMB anisotropies at angles larger than ~60 degrees, and consider whether this feature may be the signature of fluctuations expected in the R_h=ct universe.
Abstract: The emergence of several unexpected large-scale features in the cosmic microwave background (CMB) has pointed to possible new physics driving the origin of density fluctuations in the early Universe and their evolution into the large-scale structure we see today. In this paper, we focus our attention on the possible absence of angular correlation in the CMB anisotropies at angles larger than ~60 degrees, and consider whether this feature may be the signature of fluctuations expected in the R_h=ct Universe. We calculate the CMB angular correlation function for a fluctuation spectrum expected from growth in a Universe whose dynamics is constrained by the equation-of-state p=-rho/3, where p and rho are the total pressure and density, respectively. We find that, though the disparity between the predictions of LCDM and the WMAP sky may be due to cosmic variance, it may also be due to an absence of inflation. The classic horizon problem does not exist in the R_h=ct Universe, so a period of exponential growth was not necessary in this cosmology in order to account for the general uniformity of the CMB (save for the aforementioned tiny fluctuations of 1 part in 100,000 in the WMAP relic signal. We show that the R_h=ct Universe without inflation can account for the apparent absence in CMB angular correlation at angles > 60 degrees without invoking cosmic variance, providing additional motivation for pursuing this cosmology as a viable description of nature.
46 citations
TL;DR: In this paper, the authors show that the simplest model, which provides a constant equation of state for the pressure, leads to a generalization of ΛCDM, reducing to it in a particular case.
Abstract: Thanks to its fitting triumph, the ΛCDM paradigm is assumed to be the most powerful model, for describing the Universe dynamics, over much the myriad of cosmological models. Unfortunately, the quest of a self-consistent model remains not well explained, because it is not clear how to solve the problems of fine-tuning and coincidence, afflicting the ΛCDM framework; as a matter of fact, these theoretical drawbacks do not allow to consider the ΛCDM model, as the final picture of the modern cosmological scenario. Here, we show that the simplest model, which provides a constant equation of state for the pressure, leads to a generalization of ΛCDM, reducing to it in a particular case. Moreover, we highlight the physical mechanisms of this model, describing the thermodynamical reasons why a constant pressure should be negative in an expanding Universe. In addition, we fit the free parameters of our model by minimizing the chi square through the age differential method, involving a direct measurement of H.
45 citations
01 Jan 2012
TL;DR: In this paper, an attempt is made to study the universe with a closed and growing model of cosmology, where the primordial universe is a natural setting for the creation of black holes and other nonperturbative gravitational entities.
Abstract: Based on the big bang concepts- in the expanding universe, ‘rate of decrease in CMBR temperature’ is a measure of the cosmic ‘rate of expansion’. Modern standard cosmology is based on two contradictory statements. They are - present CMBR temperature is isotropic and the present universe is accelerating. In particle physics also, till today there is no practical evidence for the existence of ‘dark matter’ and ‘dark energy’. Astronomers are puzzled by the announcement that the masses of the largest objects in the Universe appear to depend on which method is used to weigh them. Recent observations and discussions at Astrophysics Research Institute (ARI) supported by the Royal Astronomical Society create new thoughts on the existence of the ‘cosmic axis of evil’. In this connection an attempt is made to study the universe with a closed and growing model of cosmology. If the primordial universe is a natural setting for the creation of black holes and other non-perturbative gravitational entities, it is also possible to assume that throughout its journey, the whole universe is a primordial (growing and rotating) cosmic black hole. Planck particle can be considered as the baby universe.
43 citations
Posted Content•
TL;DR: The DEUS "Dark Energy Universe Simulation" FUR "Full Universe Run" as mentioned in this paper was the first numerical N-body simulation of the full observable universe (DEUS-FUR), which has evolved 550 billion particles on an adaptive mesh refinement grid with more than two trillion computing points along the entire evolutionary history of the universe and across 6 order of magnitudes length scales.
Abstract: We have performed the first-ever numerical N- body simulation of the full observable universe (DEUS "Dark Energy Universe Simulation" FUR "Full Universe Run"). This has evolved 550 billion particles on an Adaptive Mesh Refinement grid with more than two trillion computing points along the entire evolutionary history of the universe and across 6 order of magnitudes length scales, from the size of the Milky Way to that of the whole observable universe. To date, this is the largest and most advanced cosmological simulation ever run. It provides unique information on the formation and evolution of the largest structure in the universe and an exceptional support to future observational programs dedicated to mapping the distribution of matter and galaxies in the universe. The simulation has run on 4752 (of 5040) thin nodes of BULL supercomputer CURIE, using more than 300 TB of memory for 10 million hours of computing time. About 50 PBytes of data were generated throughout the run. Using an advanced and innovative reduction workflow the amount of useful stored data has been reduced to 500 TBytes.
TL;DR: In this article, the Friedmann equation of a higher dimensional Friedmann-Robertson-Walker universe was obtained by modifying the volume increase and the number of degrees of freedom on the holographic surface from the entropy formulas of black hole in the Gauss-Bonnet gravity and more general Lovelock gravity.
Abstract: In a recent paper [arXiv:1206.4916] by T. Padmanabhan, it was argued that our universe provides an ideal setup to stress the issue that cosmic space is emergent as cosmic time progresses and that the expansion of the universe is due to the difference between the number of degrees of freedom on a holographic surface and the one in the emerged bulk. In this note following this proposal we obtain the Friedmann equation of a higher dimensional Friedmann-Robertson-Walker universe. By properly modifying the volume increase and the number of degrees of freedom on the holographic surface from the entropy formulas of black hole in the Gauss-Bonnet gravity and more general Lovelock gravity, we also get corresponding dynamical equations of the universe in those gravity theories.
TL;DR: In this paper, the authors reviewed all the approaches that can in principle account for the accelerated expansion of the universe, including dark energy as an item in the energy budget of the Universe, modified Einstein equations, and the use of the holographic principle.
Abstract: The kinematics and the dynamical interpretation of cosmological expansion are reviewed in a widely accessible manner with emphasis on the acceleration aspect. Virtually all the approaches that can in principle account for the accelerated expansion of the Universe are reviewed, including dark energy as an item in the energy budget of the Universe, modified Einstein equations, and, on a fundamentally new level, the use of the holographic principle.
TL;DR: In this paper, the authors studied the validity of the first law of thermodynamics for the universe bounded by event horizon with two examples and concluded that the universe may be a Bekenstein system and Einstein's equations and first law on the event horizons are equivalent.
TL;DR: In this paper, a family of spherically symmetric multi-horizon spacetimes with a vacuum dark fluid, associated with a time-dependent and spatially inhomogeneous cosmological term, is presented.
Abstract: We present a family of spherically symmetric multi-horizon spacetimes with a vacuum dark fluid, associated with a time-dependent and spatially inhomogeneous cosmological term. The vacuum dark fluid is defined in a model-independent way by the symmetry of its stress-energy tensor, i.e., its invariance under Lorentz boosts in a distinguished spatial direction ($p_r=-\rho$ for spherical symmetry), which makes the dark fluid essentially anisotropic and allows its density to evolve. The related cosmological models belong to the Lemaitre class of models with anisotropic fluids and describe a universe with several scales of vacuum energy related to phase transitions during its evolution. The typical behavior of solutions and the number of spacetime horizons are determined by the number of vacuum scales. We study in detail a model with three vacuum scales: GUT, QCD and that responsible for the present accelerated expansion. The model parameters are fixed by the observational data and by analyticity and causality conditions. We find that our Universe has three horizons. During the first inflation the Universe enters a T-region which makes the expansion irreversible. After the second phase transition at the QCD scale the Universe enters an R-region, where for a long time its geometry remains almost pseudo-Euclidean. After crossing the third horizon related to the present vacuum density, the Universe should enter the next T-region with inevitable expansion.
TL;DR: In this paper, the authors explore how inhomogeneities may affect the overall optical properties of the universe by quantifying how they can bias the redshift-distance relation in a number of toy models that mimic the real universe.
Abstract: The Universe is inhomogeneous, and yet it seems to be incredibly well-characterised by a homogeneous relativistic model. One of the current challenges is to accurately characterise the properties of such a model. In this paper we explore how inhomogeneities may affect the overall optical properties of the Universe by quantifying how they can bias the redshift-distance relation in a number of toy models that mimic the real Universe. The models that we explore are statistically homogeneous on large scales. We find that the effect of inhomogeneities is of order of a few percent, which can be quite important in precise estimation of cosmological parameters. We discuss what lessons can be learned to help us tackle a more realistic inhomogeneous universe.
TL;DR: In this paper, the generalized second law of thermodynamics for the Friedmann universe enclosed by a boundary is studied using the four well-known cosmic horizons as boundaries, namely, apparent horizon, future event horizon, Hubble horizon and particle horizon.
Abstract: In the framework of Fractional Action Cosmology (FAC), we study the generalized second law of thermodynamics for the Friedmann Universe enclosed by a boundary. We use the four well-known cosmic horizons as boundaries namely, apparent horizon, future event horizon, Hubble horizon and particle horizon. We construct the generalized second law (GSL) using and without using the first law of thermodynamics. To check the validity of GSL, we express the law in the form of four different scale factors namely emergent, logamediate, intermediate and power law. For Hubble, apparent and particle horizons, the GSL holds for emergent and logamediate expansions of the universe when we apply with and without using first law. For intermediate scenario, the GSL is valid for Hubble, apparent, particle horizons when we apply with and without first law. Also for intermediate scenario, the GSL is valid for event horizon when we apply first law but it breaks down without using first law. But for power law expansion, the GSL may be valid for some cases and breaks down otherwise.
TL;DR: In this article, the scale-invariant inflationary signatures of all single-field models which are free of ghost-like instabilities have been studied, in a way that is compatible with a nearly scale invariant spectrum of perturbations as supported by current cosmological observations.
Abstract: If the expansion of the early Universe was not close to de Sitter, the statistical imprints of the primordial density perturbation on the cosmic microwave background can be quite different from those derived in slow-roll inflation. In this paper we study the inflationary signatures of all single-field models which are free of ghost-like instabilities. We allow for a rapid change of the Hubble parameter and the speed of sound of scalar fluctuations, in a way that is compatible with a nearly scale-invariant spectrum of perturbations, as supported by current cosmological observations. Our results rely on the scale-invariant approximation, which is different from the standard slow-roll approximation. We obtain the propagator of scalar fluctuations and compute the bispectrum, keeping next-order corrections proportional to the deviation of the spectral index from unity. These theories offer an explicit example where the shape and scale-dependences of the bispectrum are highly non-trivial whenever slow-roll is not a good approximation.
TL;DR: In this paper, an alternative scheme for an emergent universe scenario where the universe is initially in a static state supported by a scalar field located in a false vacuum is proposed.
Abstract: In this work we propose an alternative scheme for an Emergent Universe scenario where the universe is initially in a static state supported by a scalar field located in a false vacuum. The universe begins to evolve when, by quantum tunneling, the scalar field decays into a state of true vacuum. The Emergent Universe models are interesting since they provide specific examples of nonsingular inflationary universes.
TL;DR: In this paper, the authors search for the existence of the late time acceleration of the universe with string fluid as the source of matter in Bianchi-V space-time and derive a deterministic solution, choosing the scale factor to be an increasing function of time that yields a time dependent deceleration parameter.
Abstract: We have searched for the existence of the late time acceleration of the universe with string fluid as the source of matter in Bianchi—V space-time. To derive a deterministic solution, we choose the scale factor to be an increasing function of time that yields a time dependent deceleration parameter, representing a model which generates a universe showing a transition from an early decelerating phase to a recent accelerating phase. The study reveals that strings dominate the early universe and eventually disappear from the universe for sufficiently large times, i.e. in the present epoch. This picture is consistent with current astronomical observations. The physical behavior of the universe is discussed in detail.
TL;DR: In this article, a class of emergent universe models is studied in the light of recent observational data, and significant constraints on model parameters are obtained from these observations, including the density parameter for a specific class of models.
Abstract: A class of emergent universe models is studied in the light of recent observational data. Significant constraints on model parameters are obtained from these observations. The density parameter for a class of models is also evaluated. Some of the models are in accordance with recent observations. Others are not of interest, yielding unrealistic present-day values of the density parameter.
TL;DR: In this article, the authors present the transition of the universe from the early decelerating phase to the current accelerating phase with viscous fluid and time-dependent cosmological constant Λ as a source of matter in Bianchi-V spacetime.
Abstract: We present the transition of the universe from the early decelerating phase to the current accelerating phase with viscous fluid and time-dependent cosmological constant Λ as a source of matter in Bianchi-V spacetime. To study the transit behaviour of the universe, we assume the scale factor as an increasing function of time, which generates a time-dependent deceleration parameter (DP). The study reveals that the cosmological term does not change its fundamental nature for ξ = const and ξ = ξ(t), where ξ is the coefficient of bulk viscosity. The Λ(t) is found to be positive and is a decreasing function of time. The same behavior was observed during recent supernovae observations. The physical behaviour of the universe is discussed in detail.
TL;DR: In this paper, the behavior of state parameter and energy density for dark energy in the framework of f(T ) gravity was investigated and it was shown that the universe takes a transition between phantom and non-phantom phases for all models except exponential and logarithmic models.
Abstract: In this paper, we investigate the behavior of equa- tion of state parameter and energy density for dark energy in the framework of f( T ) gravity. For this purpose, we use anisotropic LRS Bianchi type I universe model. The be- havior of accelerating universe is discussed for some well- known f( T ) models. It is found that the universe takes a transition between phantom and non-phantom phases for f( T ) models except exponential and logarithmic models. We conclude that our results are relativity analogous to the results of FRW universe.
TL;DR: In this paper, the authors studied the evolution of linear density perturbations in a large spherical void universe, which accounts for the acceleration of the cosmic volume expansion without introducing dark energy.
Abstract: We study the evolution of linear density perturbations in a large spherical void universe which accounts for the acceleration of the cosmic volume expansion without introducing dark energy. The density contrast of this void is not large within the light cone of an observer at the center of the void. Therefore, we describe the void structure as a perturbation with a dimensionless small parameter $\kappa$ in a homogeneous and isotropic universe within the region observable for the observer. We introduce additional anisotropic perturbations with a dimensionless small parameter $\epsilon$, whose evolution is of interest. Then, we solve perturbation equations up to order $\kappa \epsilon$ by applying second-order perturbation theory in the homogeneous and isotropic universe model. By this method, we can know the evolution of anisotropic perturbations affected by the void structure. We show that the growth rate of the anisotropic density perturbations in the large void universe is significantly different from that in the homogeneous and isotropic universe. This result suggests that the observation of the distribution of galaxies may give a strong constraint on the large void universe model.
Journal Article•
TL;DR: In this paper, it was shown that the Friedmann equation is based upon a flawed theory and that the universe is undergoing a uniform expansion, which is a major outcome of the observations of supernova events.
Abstract: Observational determination of the time evolution of the scale factor a(t) of the universe is fundamental to understanding the dynamics of the universe. Measurement [1,2] of supernovae magnitude-redshifts provided that critical data, and it is a simple procedure to determine a(t) from that data. A secondary process is then to test different dynamical theories of the universe against that data. However this did not happen, and not for the 1st time in the history of astronomy was one predetermined theory forced into the data fitting. The 1st example was Ptolemy’s fitting of his geocentric model of the solar system to the Babylonian planetary orbit data. This then required, and correctly so, that the orbits have epicycle components. This model persisted for some 1400 years, until the heliocentric model replaced the geocentric model, and for which the epicycle phenomenon then evaporated - it was merely an artifact of the incorrect geocentric model. It now appears that a similar confusion of data and model has reappeared in analysing the supernovae data, for again a simple and manifestly inadequate model of the universe, namely Newtonian gravity (NG), has been used. A generic model-independent analysis of the data reveals that the universe is undergoing a uniform expansion, see sect.2. However use of the Newtonian gravity model has resulted in a new collection of model-induced artifacts, namely “dark energy”, “dark matter”, and a claim that the universe expansion is accelerating. These artifacts also disappear once we use a model that replaces Newtonian gravity. It is usually argued that General Relativity (GR) in the form of the Friedmann equation is superior to NG, and it was the Friedmann equation that was used in analysing the supernovae data [1,2]. However in sect.3 we derive the Friedmann equation from NG in a few simple steps. This happens because GR was constructed as a generalisation of NG, and reduces to NG in the limit of low matter densities and low speeds. Alternatively, in sect.4, we show in a few simple steps, that the dynamical 3-space theory of space and gravity yields a uniformly expanding universe, and so dispenses with the “dark energy” and “dark matter” artifacts. The implication here, and in previous analyses of the dynamics of space itself, shows that NG is a flawed model of gravity, even at the level of laboratory measurements of G, bore-hole g anomalies, galactic rotation, and so on. So the Friedmann equation is based upon a flawed theory. This is in fact a major outcome of the observations of supernova events, and needs to be understood. 2 Model Independent Analysis Reveals Uniform Expansion The scale factor a(t) = r(t)=r(t0); (a(t0) ≡ 1 by definition), where r(t) are galactic separations on a sufficiently large scale, and t0 is the present moment age of the universe. It describes the time evolution of the universe assuming a homogeneous and isotropic description. In principle it may be directly extracted from magnitude-redshift data without the use of any particular dynamical model for a(t). The redshift is z = 1=a(t) − 1, and the Hubble function is H(t) = u a=a. We define H(z) by changing variables from t to z. A dimensionless luminosity distance is given by (see appendix)
TL;DR: In this article, the authors studied the general conditions required for these models to be realizable in the weak and strong dissipative regimes, and the parameters of their models were constrained from the observational data.
Abstract: Warm inflationary universe models in the context of logamediate expansion are studied. General conditions required for these models to be realizable and discussed. This study is done in the weak and strong dissipative regimes. The parameters of our models are constrained from the observational data.
TL;DR: In this article, the Veneziano ghost dark energy component was studied locally and globally by using the linearization and null-cline method developed in this paper and the energy density was generalized to be proportional to the Hawking temperature defined on the trapping horizon instead of the Hubble horizon of the FRW universe.
Abstract: In this paper, we shall study the dynamical behavior of the universe accelerated by the so called Veneziano ghost dark energy component locally and globally by using the linearization and nullcline method developed in this paper. The energy density is generalized to be proportional to the Hawking temperature defined on the trapping horizon instead of Hubble horizon of the Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the fate of the universe and present the bifurcation phenomenon of the dynamical system of the universe. It seems that the universe could be dominated by dark energy at present in some region of the parameter space.
TL;DR: This work identifies the temperature in the scalar field potential with the Hawking temperature of cosmic apparent horizon and finds that the universe could be created from a de Sitter phase which has the Planck energy density, avoiding the Big-Bang singularity.
Abstract: In the background of Friedmann-Robertson-Walker Universe, there exists Hawking radiation which comes from the cosmic apparent horizon due to quantum effect. Although the Hawking radiation on the late time evolution of the universe could be safely neglected, it plays an important role in the very early stage of the universe. In view of this point, we identify the temperature in the scalar field potential with the Hawking temperature of cosmic apparent horizon. Then we find a nonsingular universe sourced by the temperature-dependent scalar field. We find that the universe could be created from a de Sitter phase which has the Planck energy density. Thus the Big-Bang singularity is avoided.
TL;DR: In this paper, a 2.29 GHz very long baseline interferometry all-sky survey of ultra-compact radio sources is used to investigate the isotropy of the universe.
Abstract: A 2.29 GHz very long baseline interferometry all-sky survey of ultra-compact radio sources due to Preston et al. has formed the basis of a number of cosmological investigations, which examine the relationship between angular size and redshift. Here I use a sample of 468 such sources with 0.5 < z = 3.787 to investigate the isotropy of the Universe. The sample is divided into hemispherical sub-samples, over an all-sky 5 degrees X 5 degrees array, each of which is allowed to determine a value of Om, assuming that we are living in a spatially flat homogeneous isotropic ? cold dark matter model. If we regard the latter as a null hypothesis, then it fails the test the results show significant anisotropy, the smallest value of Om being towards (l, b) = (253.9,?24.1)degrees, and the largest in the opposite direction. This is close to the cosmic microwave background dipole axis, but in the obverse sense. This is interpreted as meaning that the Universe is not spatially homogeneous on the largest scales, and is better represented at late times by a spherically symmetric model with a density enhancement at its centre.
TL;DR: In this article, the authors show how magnetic fields can easily survive cosmological evolution from the inflationary era in a marginally open Friedmann universe but fail to do so, by a very wide margin, in a flat or a marginally closed universe.
Abstract: The detection of magnetic fields at high redshifts, and in empty intergalactic space, supports the idea that cosmic magnetism has a primordial origin. Assuming that Maxwellian electromagnetism and general relativity hold, and without introducing any new physics, we show how the observed magnetic fields can easily survive cosmological evolution from the inflationary era in a marginally open Friedmann universe but fail to do so, by a very wide margin, in a flat or a marginally closed universe. Magnetic fields evolve very differently in open and closed Friedmann models. The existence of significant magnetic fields in the universe today, that require primordial seeding, may therefore provide strong evidence that the universe is marginally open rather than marginally closed.