Showing papers on "Particle horizon published in 2003"
TL;DR: The 95% confidence level lower limit on the age of the Universe of 11.2 billion years means that the three fundamental observables in cosmology now independently support the case for a dark energy–dominated Universe.
Abstract: Recent observations of stellar globular clusters in the Milky Way Galaxy, combined with revised ranges of parameters in stellar evolution codes and new estimates of the earliest epoch of globular cluster formation, result in a 95% confidence level lower limit on the age of the Universe of 11.2 billion years. This age is inconsistent with the expansion age for a flat Universe for the currently allowed range of the Hubble constant, unless the cosmic equation of state is dominated by a component that violates the strong energy condition. This means that the three fundamental observables in cosmology-the age of the Universe, the distance-redshift relation, and the geometry of the Universe-now independently support the case for a dark energy-dominated Universe.
335 citations
TL;DR: In the last decade, a series of advances in both theory and technology have launched cosmology into its most exciting period of discovery yet as discussed by the authors, and promising ideas for understanding the basic features of the universe are being tested, and deep connections between physics on the smallest scales and on the largest scales are being revealed.
Abstract: Revolutionary advances in both theory and technology have launched cosmology into its most exciting period of discovery yet. Unanticipated components of the universe have been identified, promising ideas for understanding the basic features of the universe are being tested, and deep connections between physics on the smallest scales and on the largest scales are being revealed.
172 citations
TL;DR: In this paper, the properties of the behavior of classical cosmological perturbations when the universe experiences a bounce are investigated. But the authors focus on the case where gravity is described by general relativity and the matter content has a single component, namely a scalar field in a closed geometry.
Abstract: We clarify the properties of the behavior of classical cosmological perturbations when the Universe experiences a bounce. This is done in the simplest possible case for which gravity is described by general relativity and the matter content has a single component, namely, a scalar field in a closed geometry. We show in particular that the spectrum of scalar perturbations can be affected by the bounce in a way that may depend on the wave number, even in the large scale limit. This may have important implications for string motivated models of the early Universe.
117 citations
TL;DR: In this paper, the authors describe a class of models where the flatness of the universe can be resolved by fine-tuning the total number of e-folds to be sufficiently small.
Abstract: It is very difficult to obtain a realistic model of a closed inflationary universe. Even if one fine-tunes the total number of e-folds to be sufficiently small, the resulting universe typically has large density perturbations on the scale of the horizon. We describe a class of models where this problem can be resolved. The models are unattractive and fine-tuned, so the flatness of the universe remains a generic prediction of inflationary cosmology. Nevertheless one should keep in mind that with the fine-tuning at the level of about one percent one can obtain a semi-realistic model of a closed inflationary universe. The spectrum of density perturbations in this model may have a cut-off on the scale of the horizon. Similar approach may be valid in application to a compact inflationary universe with a nontrivial topology.
113 citations
TL;DR: In this article, the authors describe a class of models where the flatness of the universe can be resolved by fine-tuning the total number of e-folds to be sufficiently small.
Abstract: It is very difficult to obtain a realistic model of a closed inflationary universe. Even if one fine-tunes the total number of e-folds to be sufficiently small, the resulting universe typically has δρ/ρ~ΔT/T = O(1) on the scale of the horizon. We describe a class of models where this problem can be resolved. The models are unattractive and fine-tuned, so the flatness of the universe remains a generic prediction of inflationary cosmology. Nevertheless one should keep in mind that with the fine-tuning at the level of about one per cent one can obtain a semi-realistic model of an inflationary universe with Ω>1. The spectrum of density perturbations in this model may have a cut-off on the scale of the horizon. A similar approach may be valid in application to a compact inflationary universe with a nontrivial topology.
105 citations
TL;DR: In this article, a method to probe the early universe and its evolution using the stochastic gravitational wave background from inflation was proposed, which is a small deviation from purely radiatio...
Abstract: We propose a method to probe the equation of state of the early universe and its evolution, using the stochastic gravitational wave background from inflation. A small deviation from purely radiatio...
104 citations
TL;DR: In this article, the authors simulate the future evolution of the observed inhomogeneities in the local universe assuming that the global expansion rate is dominated by a cosmological constant, and they find that within two Hubble times (∼30 billion years) from the present epoch, large-scale structures will freeze in co-moving coordinates and the mass distribution of bound objects will stop evolving.
91 citations
TL;DR: In this paper, it was shown that the data from SNAP and Planck satellites may extend the bound on the 'doomsday' time to 40 billion years at the 95% confidence level.
Abstract: Recently it was found, in a broad class of models, that the dark energy density may change its sign during the evolution of the universe. This may lead to a global collapse of the universe within the time tc ~ 1010–1011 years. Our goal is to find what bounds on the future lifetime of the universe can be placed by the next generation of cosmological observations. As an example, we investigate the simplest model of dark energy with a linear potential V() = V0(1 + α). This model can describe the present stage of acceleration of the universe if α is small enough. However, eventually the field rolls down, V() becomes negative, and the universe collapses. The existing observational data indicate that the universe described by this model will collapse not earlier than tc 10 billion years from the present moment. We show that the data from SNAP and Planck satellites may extend the bound on the `doomsday' time to tc 40 billion years at the 95% confidence level.
86 citations
TL;DR: In this paper, the authors studied the time evolution of the corresponding effective 4D cosmological model supplemented by cold dark matter and showed that it is marginally possible to describe observational data for the late-time cosmic acceleration in this model.
Abstract: Recently it was observed that the hyperbolic compactification of M/string theory related to S-branes may lead to a transient period of acceleration of the universe. We study time evolution of the corresponding effective 4d cosmological model supplemented by cold dark matter and show that it is marginally possible to describe observational data for the late-time cosmic acceleration in this model. However, investigation of the compactification 11d → 4d suggests that the Compton wavelengths of the KK modes in this model are of the same order as the size of the observable part of the universe. Assuming that this problem, as well as several other problems of this scenario, can be resolved, we propose a possible solution of the cosmological coincidence problem due to the relation between the dark energy density and the effective dimensionality of the universe.
69 citations
TL;DR: In this paper, it was shown that in many models based on supergravity, the dark energy eventually becomes negative and the universe collapses within a time comparable to the present age of the universe.
Abstract: It is often assumed that in the course of the evolution of the Universe, the dark energy either vanishes or becomes a positive constant. However, recently it was shown that in many models based on supergravity, the dark energy eventually becomes negative and the Universe collapses within a time comparable to the present age of the Universe. We will show that this conclusion is not limited to the models based on supergravity: in many models describing the present stage of acceleration of the Universe the dark energy eventually becomes negative, which triggers the collapse of the Universe within the time t = 1010 –1011 years. Theories of this type have certain distinguishing features that can be tested by cosmological observations.
62 citations
TL;DR: In this paper, a cosmological D bound on the entropy of matter in the universe was introduced, and the Friedmann equation was shown to coincide with the Cardy-Verlinde formula.
Abstract: We discuss the holographic principle in a radiation-dominated, closed Friedmann-Robertson-Walker universe with a positive cosmological constant. By introducing a cosmological D bound on the entropy of matter in the universe, we can write the Friedmann equation governing the evolution of the universe in the form of the Cardy formula. When the cosmological D bound is saturated, the Friedmann equation coincides with the Cardy-Verlinde formula describing the entropy of radiation in the universe. As a concrete model, we consider a brane universe in the background of Schwarzschild-de Sitter black holes. It is found that the cosmological D bound is saturated when the brane crosses the black hole horizon of the background. At that moment, the Friedmann equation coincides with the Cardy-Verlinde formula describing the entropy of radiation matter on the brane.
TL;DR: In this paper, the authors examined the possibility that thermal, rather than quantum, fluctuations are responsible for seeding the structure of our universe and found that while the thermalization condition leads to nearly Gaussian statistics, a Harrisson-Zeldovich spectrum for the primordial fluctuations can only be achieved in very special circumstances.
Abstract: We examine the possibility that thermal, rather than quantum, fluctuations are responsible for seeding the structure of our universe. We find that while the thermalization condition leads to nearly Gaussian statistics, a Harrisson-Zeldovich spectrum for the primordial fluctuations can only be achieved in very special circumstances. These depend on whether the universe gets hotter or colder in time, while the modes are leaving the horizon. In the latter case we find a no-go theorem which can only be avoided if the fundamental degrees of freedom are not particlelike, such as in string gases near the Hagedorn phase transition. The former case is less forbidding, and we suggest two potentially successful ``warming universe'' scenarios. One makes use of the Phoenix universe, the other of ``phantom'' matter.
TL;DR: In this paper, the authors use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the universe and explain why these misconceptions do not violate special relativity and link these concepts to observational tests.
Abstract: We use standard general relativity to illustrate and clarify several common misconceptions about the expansion of the Universe. To show the abundance of these misconceptions we cite numerous misleading, or easily misinterpreted, statements in the literature. In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests. Attempts to restrict recession velocities to less than the speed of light require a special relativistic interpretation of cosmological redshifts. We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23 sigma.
TL;DR: In this paper, the authors apply the scale-relativistic resolution transformation to scale transformations in the early universe and propose a generalization of fundamental dilations laws, which are invariant under dilations.
Abstract: The principle of relativity, when it is applied to scale transformations, leads to the suggestion of a generalization of fundamental dilations laws. These new specialscale-relativistic resolution transformations involve log-Lorentz factors and lead to the occurrence of a minimal and of a maximal length-scale in nature, which are invariant under dilations. The minimal length-scale, that replaces the zero from the viewpoint of its physical properties, is identied with the Planck-length lP , and the maximal scale, that replaces innit y, is identied with the cosmic scale I L = 1=2 , where is the cosmological constant. The new interpretation of the Planck scale has several implications for the structure and history of the early Universe: we consider the questions of the origin, of the status of physical laws at very early times, of the horizon / causality problem and of uctuations at recombination epoch. The new interpretation of the cosmic scale has consequences for our knowledge of the present universe, concerning in particular Mach’s principle, the large number coincidence, the problem of the vacuum energy density, the nature and the value of the cosmological constant. The value (theroretically predicted ten years ago) of the scaled cosmological constant = 0:75 0:15 is now supported by several dieren t experiments (Hubble diagram of Supernovae, Boomerang measurements, gravitational lensing by clusters of galaxies). The scale-relativity framework also allows one to suggest a general solution to the missing mass problem, and to make theoretical predictions of fundamental energy scales, thanks to the interpretation of new structures in scale space: fractal /classical transitions as Compton lengths, mass-coupling relations and critical value 4 2 of inverse couplings. Among them, we nd a structure at 3:27 0:26 10 20 eV, which agrees closely with the observed highest energy cosmic rays at 3:2 0:9 10 20 eV, and another at 5:3 10 3 eV, which corresponds to the typical neutrino mass needed
TL;DR: In this article, the authors proposed a model in which the cosmic effective Yang-Mills condensate familiar in particle physics plays the role of the dark energy that causes the acceleration of the universe.
Abstract: Recent observations of large scale structure of the Universe, especially that of Type Ia supernovae, indicate that the Universe is flat and is accelerating, and that the dominant energy density in the Universe is the cosmic dark energy. We propose a model in which the cosmic effective Yang-Mills condensate familiar in particle physics plays the role of the dark energy that causes the acceleration of the Universe. Since the quantum effective Yang-Mills field in certain states has the equation of state py = −ρy, when employed as the cosmic matter source, it naturally results in an accelerating expansion of the Universe. With the matter components (Ωm ∼ 1/3) being added into the model, the composition of YM condensate and matter components can give rise to the desired equation of state w ∼ −2/3 for the Universe.
TL;DR: In this paper, the authors contrast features of simple varying speed of light (VSL) cosmologies with inflationary universe models and show that they face problems explaining the cosmological isotropy problem.
TL;DR: In this article, the back-reaction effect of the neutrino field at finite temperature in the background of the static Einstein universe is investigated, and a relationship between the temperature of the universe and its radius is found.
Abstract: The back-reaction effect of the neutrino field at finite temperature in the background of the static Einstein universe is investigated. A relationship between the temperature of the universe and its radius is found. As in previously studied cases of the massless scalar field and the photon field, this relation exhibits a minimum radius below which no self-consistent solution for the Einstein field equation can be found. A maximum temperature marks the transition from a vacuum-dominated state to the radiation-dominated state universe. In light of the results obtained for the scalar, neutrino and photon fields, the role of the back reaction of quantum fields in controlling the value of the cosmological constant is briefly discussed.
TL;DR: In this article, the time-varying density of D-branes and anti-Dbranes in an expanding universe is calculated and it is shown that small dimension Dbranes annihilate more slowly than high dimension branes, which leads to an attractive dynamical way to create a realistic braneworld scenario.
Abstract: The time-varying density of D-branes and anti-D-branes in an expanding universe is calculated. The D-brane anti-brane annihilation rate is shown to be too small to compete with the expansion rate of a FRW type universe and the branes over-close the universe. This brane problem is analogous to the old monopole problem. Interestingly however, it is shown that small dimension D-branes annihilate more slowly than high dimension branes. Hence, an initially brany universe may be filled with only low dimension branes at late times. When combined with an appropriate late inflationary theory this leads to an attractive dynamical way to create a realistic braneworld scenario.
TL;DR: In this paper, a spatially homogeneous and isotropic Robertson-Walker model with zero-curvature of the universe is studied in Saez-Ballester scalar-tensor theory.
Abstract: A spatially homogeneous and isotropic Robertson-Walker model with zero-curvature of the universe is studied in Saez-Ballester scalar-tensor theory. Exact solutions of the field equations are obtained for two different early phases of the universe viz. the inflationary and the radiation-dominated phases by using gamma-law equation of state p=(γ-1)ρ in the presence of perfect fluid. The γ-index describing the material content varies continuously with cosmic time so that in the course of its evolution, the universe goes through a transition from an inflationary phase to a radiation-dominated phase. The coupling parameterω is allowed to depend on the cosmic time. The nature of scalar field and other physical significance have also been discussed.
TL;DR: In this paper, a stability criterion is derived in general relativity for self-similar solutions with a scalar field and those with a stiff fluid, which is a perfect fluid with the equation of state $P=\rho.
Abstract: A stability criterion is derived in general relativity for self-similar solutions with a scalar field and those with a stiff fluid, which is a perfect fluid with the equation of state $P=\rho$. A wide class of self-similar solutions turn out to be unstable against kink mode perturbation. According to the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be a critical solution for the spherical collapse of a stiff fluid if we allow sufficiently small discontinuity in the density gradient field in the initial data sets. The self-similar scalar-field solution, which was recently found numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19} 6359), is also unstable. Both the flat Friedmann universe with a scalar field and that with a stiff fluid suffer from kink instability at the particle horizon scale.
TL;DR: In this paper, the authors investigate the cosmological consequences of a braneworld theory, which incorporates time variations in the gravitational coupling G and the Cosmological term Λ(4), and demonstrate that the universe must recollapse, if it is embedded in an anti-de Sitter five-dimensional bulk.
Abstract: We investigate the cosmological consequences of a braneworld theory which incorporates time variations in the gravitational coupling G and the cosmological term Λ(4). We analyse in detail the model where Gdot/G ~ H and Λ(4) ~ H2, which seems to be favoured by observations. We show that these conditions single out models with flat space sections. We determine the behaviour of the expansion scale factor, as well as the variation of G, Λ(4) and H, for different possible scenarios where the bulk cosmological constant, Λ(5), can be zero, positive or negative. We demonstrate that the universe must recollapse, if it is embedded in an anti-de Sitter five-dimensional bulk, which is the usual case in brane models. We evaluate the cosmological parameters, using some observational data, and show that we are nowhere near the time of recollapse. We conclude that the models with zero and negative bulk cosmological constants agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameters. The age of the universe, even in the recollapsing case, is much larger than in the Friedmann–Robertson–Walker universe.
TL;DR: In this paper, a (4 + D)-dimensional Kaluza-Klein cosmology with a Robertson-Walker type metric having two scale factors a and R was studied, corresponding to a D-dimensional internal space and four-dimensional universe, respectively.
Abstract: We study a (4 + D)-dimensional Kaluza–Klein cosmology with a Robertson–Walker type metric having two scale factors a and R, corresponding to a D-dimensional internal space and four-dimensional universe, respectively. By introducing exotic matter as the spacetime part of the higher dimensional energy–momentum tensor, a four-dimensional decaying cosmological term appears as Λ ~ R−2, playing the role of an evolving dark energy in the universe. The resulting field equations yield the exponential solutions for the scale factors. These exponential behaviours may account for the dynamical compactification of extra dimensions and the accelerating expansion of the four-dimensional universe in terms of the Hubble parameter. The acceleration of the universe may be explained by the negative pressure of the exotic matter. It is shown that the rate of compactification of higher dimensions depends on the dimension, D. We then obtain the Wheeler–DeWitt equation and find the general exact solutions in D dimensions. A good correspondence between the classical solutions and the Wheeler–DeWitt solutions in any dimension, D, is obtained.
TL;DR: In this article, the instability against spatially homogeneous and anisotropic perturbations of the Kantowski-Sachs type during different cosmological epochs was analyzed and it was shown that the universe must be open or flat if it underwent a matter-dominated and/or radiation-dominated era in its past evolution.
Abstract: In this paper, by analyzing the instability against spatially homogeneous and anisotropic perturbations of the Kantowski-Sachs type during different cosmological epochs, we show that it is a theoretical consequence of general relativity that the KS universe must be open or flat if it underwent a matter-dominated and/or radiation-dominated era in its past evolution, which theoretically confirms the flatness of our observable Universe.
TL;DR: In this paper, the existence of mechanisms of transition to global chaos in a closed Friedmann-Robertson-Walker universe with a massive conformally coupled scalar field is studied.
Abstract: In this work we study the existence of mechanisms of transition to global chaos in a closed Friedmann-Robertson-Walker universe with a massive conformally coupled scalar field. We propose a complexification of the radius of the universe so that the global dynamics can be understood. We show numerically the existence of heteroclinic connections of the unstable and stable manifolds to periodic orbits associated to the saddle-center equilibrium points. We find two bifurcations which are crucial in creating non-collapsing universes both in the real and imaginary version of the models. The techniques presented here can be employed in any cosmological model.
TL;DR: In this paper, the authors studied the big bounce singularity of a simple five-dimensional cosmological model and found that it is an event horizon at which the scale factor and the mass density of the universe are finite, while the pressure undergoes a sudden transition from negative infinity to positive infinity.
Abstract: The big bounce singularity of a simple five-dimensional cosmological model is studied. Contrary to the standard big bang space-time singularity, this big bounce singularity is found to be an event horizon at which the scale factor and the mass density of the universe are finite, while the pressure undergoes a sudden transition from negative infinity to positive infinity. By using coordinate transformation it is also shown that before the bounce the universe contracts deflationary. According to the proper-time, the universe may have existed for an infinitely long time.
TL;DR: In this paper, the authors studied a quantum theory of the early universe with a negative effective cosmological constant and proved that the theory is a quantum quantum theory with a constant constant.
Abstract: The paper studies a quantum theory of the early Universe with a negative effective cosmological constant.
TL;DR: In this paper, an expanding anisotropic universe is found to isotropize during its expansion, but a static universe cannot isotropise, and the cosmological constant decreases with time as ⁄ / t i2.
Abstract: Exact solutions for a model with variable G, ⁄ and bulk viscosity are obtained. Inflationary solutions with constant (de Sitter-type) and variable energy density are found. An expanding anisotropic universe is found to isotropize during its expansion but a static universe cannot isotropize. The gravitational constant is found to increase with time and the cosmological constant decreases with time as ⁄ / t i2 .
TL;DR: In this paper, the authors review recent measurements of the expansion rate, geometry, age, matter content, and equation of state of the universe, and discuss the implications for our understanding of cosmology.
Abstract: In the past decade, observational cosmology has had one of the most exciting periods in the past century. The precision with which we have been able to measure cosmological parameters has increased tremendously, while at the same time, we have been surprised beyond our wildest dreams by the results. I review here recent measurements of the expansion rate, geometry, age, matter content, and equation of state of the universe, and discuss the implications for our understanding of cosmology.
TL;DR: In this paper, the authors demonstrate an inflationary solution to the cosmological horizon problem during the Hagedorn regime in the early universe, where the observable universe is confined to three spatial dimensions embedded in higher dimensions.