Showing papers on "Cosmology published in 1997"
Book•
13 Jul 1997
TL;DR: In this article, the Szekeres-Szafron family of solutions and the Stephani-Barnes family of solution are compared in an inhomogeneous universe.
Abstract: List of illustrations Preface Acknowledgements 1 Preliminaries 2 The Szekeres-Szafron family of solutions 3 Physics and cosmology in an inhomogeneous universe 4 The Stephani-Barnes family of solutions 5 Solutions with null radiation 6 Solutions with a 'stiff fluid'/scalar field source 7 Other solutions 8 Averaging out inhomogeneities of geometry and matter in cosmological models 9 Comments Appendices Bibliography Index
664 citations
Posted Content•
TL;DR: Carroll as discussed by the authors presented one semester's worth of lectures on introductory general relativity for beginning graduate students in physics Topics include manifolds, Riemannian geometry, Einstein's equations, and three applications: gravitational radiation, black holes, and cosmology.
Abstract: These notes represent approximately one semester’s worth of lectures on introductory general relativity for beginning graduate students in physics Topics include manifolds, Riemannian geometry, Einstein’s equations, and three applications: gravitational radiation, black holes, and cosmology Individual chapters, and potentially updated versions, can be found at http://itpucsbedu/~carroll/notes/
352 citations
TL;DR: In this article, the effective energy-momentum tensor (EMT) for cosmological perturbations and the back-reaction problem were formulated in a gauge-invariant manner.
Abstract: We study the effective energy-momentum tensor (EMT) for cosmological perturbations and formulate the gravitational back-reaction problem in a gauge-invariant manner. We analyze the explicit expressions for the EMT in the cases of scalar metric fluctuations and of gravitational waves and derive the resulting equations of state. The formalism is applied to investigate the back-reaction effects in chaotic inflation. We find that for long wavelength scalar and tensor perturbations, the effective energy density is negative and thus counteracts any preexisting cosmological constant. For scalar perturbations during an epoch of inflation, the equation of state is de Sitter-like.
293 citations
Book•
01 Jan 1997
TL;DR: In this paper, the authors discuss the origins of modern cosmology and the creation of the Inflationary Universe, and the after-math of discovery and creation of a new inflationary universe.
Abstract: * The Ultimate Free Lunch * The Cosmic Vista from Ithaca, New York * The Birth of Modern Cosmology * Echoes of a Scorching Past * Condensation of the Primordial Soup * Matters of Matter and Antimatter * The Particle Physics Revolution of the 1970s * Grand Unified Theories * Combating the Magnetic Monopole Menace * The Inflationary Universe * The Aftermath of Discovery * The New Inflationary Universe * Wrinkles on a Smooth Background * Observational Clues from Deep Below and Far Beyond * The Eternally Existing, Self-Reproducing Inflationary Universe * Wormholes and the Creation of Universes in the Laboratory * A Universe Ex Nihilo * Epilogue
247 citations
TL;DR: Lower bounds on the cosmic baryon density from the requirement that the high-redshift intergalactic medium (IGM) contain enough neutral hydrogen to produce the observed Lyα absorption in quasar spectra were derived in this article.
Abstract: We derive lower bounds on the cosmic baryon density from the requirement that the high-redshift intergalactic medium (IGM) contain enough neutral hydrogen to produce the observed Lyα absorption in quasar spectra. These analytic bounds follow from a key theoretical assumption—that absorbing structures are on average no more extended in redshift space than in real space—which is likely to hold in the gravitational instability picture of the Lyα forest, independently of the details of the cosmological model. The other ingredients that enter these bounds are an estimate of (or lower limit to) the intensity of the photoionizing UV background from quasars, a temperature T ~ 104 K for the "warm" photoionized IGM that produces most of the Lyα absorption, a value of the Hubble constant, and observational estimates of the mean Lyα flux decrement or, for a more restrictive bound, the distribution function P(τ) of Lyα optical depths. With plausible estimates of the quasar UV background and , the mean decrement bound implies a baryon density parameter Ωb 0.0125 h-2, where h ≡ H0/(100 km s-1 Mpc-1). A recent observational determination of P(τ) implies that Ωb 0.0125 h-2 even for a conservative estimate of the quasar UV background, and Ωb 0.018 h-2 for a more reasonable estimate. These bounds are consistent with recent low estimates of the primordial deuterium-to-hydrogen ratio (D/H)P, which imply that Ωb ≈ 0.025 h-2 when combined with standard big bang nucleosynthesis. Since the bounds account only for baryons in the warm IGM, their combination with the nucleosynthesis constraint implies that most of the baryons in the universe at z ~ 2-4 were distributed in diffuse intergalactic gas rather than in stars or compact dark objects. The P(τ) bound on Ωb is incompatible with some recent high estimates of (D/H)P, unless one drops the assumptions of standard big bang nucleosynthesis or abandons the idea that Lyα forest lines originate in the smooth, large-scale structures of photoionized gas that arise in gravitational instability theories.
210 citations
TL;DR: In this paper, the authors explore the implications of such dynamical {Lambda} models for the formation of large-scale structure and find that there are dynamical models for which the amplitude of the COBE-normalized spectrum matches the observations.
Abstract: Models of structure formation with a cosmological constant {Lambda} provide a good fit to the observed power spectrum of galaxy clustering. However, they suffer from several problems. Theoretically, it is difficult to understand why the cosmological constant is so small in Planck units. Observationally, while the power spectra of cold dark matter plus {Lambda} models have approximately the right shape, the COBE-normalized amplitude for a scale-invariant spectrum is too high, requiring galaxies to be antibiased relative to the mass distribution. Attempts to address the first problem have led to models in which a dynamical field supplies the vacuum energy, which is thereby determined by fundamental physics scales. We explore the implications of such dynamical {Lambda} models for the formation of large-scale structure. We find that there are dynamical models for which the amplitude of the COBE-normalized spectrum matches the observations. We also calculate the cosmic microwave background anisotropies in these models and show that the angular power spectra are distinguishable from those of standard cosmological constant models. {copyright} {ital 1997} {ital The American Physical Society}
199 citations
TL;DR: In this paper, general features of β-function equations for spatially flat, (d+ 1)-dimensional cosmological backgrounds at lowest order in the string-loop expansion, but to all orders in α′, are discussed.
198 citations
TL;DR: Current observations suggest that the “strong energy condition” was violated sometime between the epoch of galaxy formation and the present, which implies that no possible combination of “normal” matter is capable of fitting the observational data.
Abstract: The energy conditions of Einsteinian gravity (classical general relativity) do not require one to fix a specific equation of state. In a Friedmann-Robertson-Walker universe where the equation of state for the cosmological fluid is uncertain, the energy conditions provide simple, model-independent, and robust bounds on the behavior of the density and look-back time as a function of red shift. Current observations suggest that the “strong energy condition” was violated sometime between the epoch of galaxy formation and the present. This implies that no possible combination of “normal” matter is capable of fitting the observational data.
193 citations
TL;DR: In this paper, the authors discuss the potential of CBR anisotropy or polarization and of direct detection by the laser-interferometers to test the key prediction of inflation, which is to extend our understanding of the Universe to as early as 10 −32 sec and open a window on physics at energies of order 10 15 GeV.
Abstract: Introduction Inflation addresses most of the fundamental problems in cosmology – the origin of the flatness, large-scale smoothness, and small density inhomogeneities needed to seed all the structure seen in the Universe today. If correct, it would extend our understanding of the Universe to as early as 10 −32 sec and open a window on physics at energies of order 10 15 GeV. However, at the moment there is little evidence to confirm or to contradict inflation and no standard model of inflation. The key to testing inflation is to focus on its three basic predictions [1]: spatially flat Universe (total energy density equal to the critical energy density); almost scaleinvariant spectrum of gaussian density perturbations [2]; and almost scale-invariant spectrum of stochastic gravitational waves [3]. The first two predictions have important implications: the existence of nonbaryonic dark matter, as big-bang nucleosynthesis precludes baryons from contribution more than about 10% of the critical density [4], and the cold dark matter scenario for structure formation, based upon the idea that the nonbaryonic dark matter is slowly moving elementary particles left over from the earliest moments [5,6]. A host of cosmological observations are now beginning to sharply test the first two predictions [6]. Gravity waves are a telling test and probe of inflation: They provide a consistency check (see below); they are essential to learning about the scalar potential that drives inflation [7]; and they are a compelling signature of inflation – both a flat Universe and scale-invariant density perturbations were advocated before inflation. Detecting inflation-produced gravity waves presents a great experimental challenge [8]. In this Letter we discuss the potential of CBR anisotropy or polarization and of direct detection by the laser-interferometers to test this key prediction of inflation. Quantum Fluctuations The (Fourier) spectra of metric fluctuations excited during inflation are characterized by power laws in wavenumber k, k n for density perturbations (scalar metric fluctuations) and k nT −3 for gravity waves (tensor metric fluctuations). Scale invariance for density perturbations (n = 1) corresponds to fluctuations in the Newtonian potential that are independent of wavenumber; scale invariance for gravity waves (nT = 0) corresponds to dimensionless horizon-crossing strain amplitudes that are independent of wavenumber. The power-law indices are related to the scalar field potential, V (�), that drives inflation: n − 1 = − m 2
175 citations
TL;DR: In this article, the authors present evidence for a quasi-regular three-dimensional network of rich superclusters and voids, with the regions of high density separated by ∼120 Mpc.
Abstract: ACCORDING to the favoured models for the formation of large-scale structure in the Universe (in which the dynamics of the Universe is dominated by cold dark matter), the distribution of galaxies and clusters of galaxies should be random on large scales. It therefore came as a surprise when a periodicity was reported1 in the distribution of high-density regions of galaxies in the directions of the Galactic poles, although the apparent lack of periodicity in other directions led to the initial report being regarded as a statistical anomaly2. A subsequent study3–6 also claimed evidence for periodicity on the same scale, but the statistical significance of this result was uncertain due to the small number of clusters used. Here, using a new compilation7 of available data on galaxy clusters, we present evidence for a quasi-regular three-dimensional network of rich superclusters and voids, with the regions of high density separated by ∼120 Mpc. If this reflects the distribution of all matter (luminous and dark), then there must exist some hitherto unknown process that produces regular structure on large scales.
TL;DR: In this paper, the authors show that the strong energy condition (SEC) is violated at some time between the epoch of galaxy formation and the present, which implies that no possible combination of {ital {open_quotes}normal{close-quotes}} matter is capable of fitting the observational data.
Abstract: The energy conditions of Einstein gravity (classical general relativity) are designed to extract as much information as possible from classical general relativity without enforcing a particular equation of state for the stress energy. This systematic avoidance of the need to specify a particular equation of state is particularly useful in a cosmological setting {emdash} since the equation of state for the cosmological fluid in a Friedmann-Robertson-Walker-type universe is extremely uncertain. I shall show that the energy conditions provide simple and robust bounds on the behavior of both the density and look-back time as a function of redshift. I shall show that current observations {ital suggest} that the so-called {ital strong energy condition} (SEC) is violated at some time between the epoch of galaxy formation and the present. This implies that no possible combination of {ital {open_quotes}normal{close_quotes}} matter is capable of fitting the observational data. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: This paper decompose the damping tail of CMB anisotropies into a series of transfer functions representing individual physical effects, which can aid in the reconstruction of the cosmological model from small-scale CMBanisotropy data.
Abstract: By decomposing the damping tail of cosmic microwave background (CMB) anisotropies into a series of transfer functions representing individual physical effects, we provide ingredients that will aid in the reconstruction of the cosmological model from small-scale CMB anisotropy data. We accurately calibrate the model-independent effects of diffusion and reionization damping, which provide potentially the most robust information on the background cosmology. Removing these effects, we uncover model-dependent processes, such as the acoustic peak modulation and gravitational enhancement, that can help distinguish between alternate models of structure formation and provide windows into the evolution of fluctuations at various stages in their growth.
TL;DR: In this article, the cosmological evolution of free massless vector or tensor fields minimally coupled to gravity is analyzed, and it is shown that there are some unstable solutions for these fields in the de Sitter background.
Abstract: The cosmological evolution of free massless vector or tensor (but not gauge) fields minimally coupled to gravity is analyzed. It is shown that there are some unstable solutions for these fields in the de Sitter background. The back reaction of the energy-momentum tensor of such solutions to the original cosmological constant exactly cancels the latter and the expansion regime changes from the exponential to the power-law one. In contrast with the adjustment mechanism realized by a scalar field the gravitational coupling constant in this model is time independent and the resulting cosmology may resemble the realistic one.
TL;DR: In this article, a general-relativistic treatment of cosmological perturbations in a universe permeated by a large-scale primordial magnetic field using the Ellis - Bruni gauge-invariant formalism is provided.
Abstract: We provide a fully general-relativistic treatment of cosmological perturbations in a universe permeated by a large-scale primordial magnetic field using the Ellis - Bruni gauge-invariant formalism. The exact nonlinear equations for general-relativistic magnetohydrodynamic evolution are derived. A number of applications are made: the behaviour of small perturbations to Friedmann universes is studied; a comparison is made with earlier Newtonian treatments of cosmological perturbations and some effects of inflationary expansion are examined.
TL;DR: In the application of relativistic mechanics to cosmology, it has been usual to consider homogeneous models of the universe, filled with an idealized fluid, which at any given time has the same properties throughout the whole of its spatial extent.
Abstract: In the application of relativistic mechanics and relativistic thermodynamics to cosmology, it has been usual to consider homogeneous models of the universe, filled with an idealized fluid, which at any given time has the same properties throughout the whole of its spatial extent. This procedure has a certain heuristic justification on account of the greater mathematical simplicity of homogeneous as compared with non-homogeneous models, and has a measure of observational justification on account of the approximate uniformity in the large scale distribution of extra-galactic nebulae, which is found out to the some 108 light-years which the Mount Wilson 100-inch telescope has been able to penetrate. Nevertheless, it is evident that some preponderating tendency for inhomogeneities to disappear with time would have to be demonstrated, before such models could be used with confidence to obtain extrapolated conclusions as to the behavior of the universe in very distant regions or over exceedingly long periods of time.
TL;DR: In this article, the authors study the evolution of the domain wall network for a variety of field configurations in two and three dimensions and quantify the rate at which the walls disappear, and conclude that there is no domain wall problem in the post-inflationary universe for weakly coupled fields.
Abstract: Discrete symmetries are commonplace in field theoretical models but pose a severe problem for cosmology since they lead to the formation of domain walls during spontaneous symmetry breaking in the early universe. However if one of the vacuua is favoured over the others, either energetically, or because of initial conditions, it will eventually come to dominate the universe. Using numerical methods, we study the evolution of the domain wall network for a variety of field configurations in two and three dimensions and quantify the rate at which the walls disappear. Good agreement is found with a recent analytic estimate of the termination of the scaling regime of the wall network. We conclude that there is no domain wall problem in the post-inflationary universe for a weakly coupled field which is not in thermal equilibrium.
TL;DR: In this article, the authors proposed to use the Mg$-\sigma relation to calibrate massive cluster elliptical as cosmological standard rods using the Fundamental Plane relation combined with a correction for luminosity evolution.
Abstract: We explore the possibility to calibrate massive cluster ellipticals as cosmological standard rods using the Fundamental Plane relation combined with a correction for luminosity evolution. Though cluster ellipticals certainly formed in a complex way, their passive evolution out to redshifts of about 1 indicates that basically all major merging and accretion events took place at higher redshifts. Therefore, a calibration of their luminosity evolution can be attempted. We propose to use the Mg$-\sigma$ relation for that purpose because it is independent of distance and cosmology. We discuss a variety of possible caveats, ranging from dynamical evolution to uncertainties in stellar population models and evolution corrections to the presence of age spread. Sources of major random and systematic errors are analysed as well. We apply the described procedure to nine elliptical galaxies in two clusters at $z=0.375$ and derive constraints on the cosmological model. For the best fitting $\Lambda$-free cosmological model we obtain: $q_o \approx 0.1$, with 90% confidence limits being $0 < q_o < 0.7$ (the lower limit being due to the presence of matter in the Universe). If the inflationary scenario applies (i.e. the Universe has flat geometry), then, for the best fitting model, matter and $\Lambda$ contribute about equally to the critical cosmic density (i.e. $\Omega_m \approx \Omega_\Lambda \approx 0.5$). With 90% confidence $\Omega_\Lambda$ should be smaller than 0.9.
TL;DR: In this paper, an alternative to Einstein Gravity that satisfies the equivalence principle and automatically passes all classical weak-field tests (GM/r approx 10^{-6}) was presented.
Abstract: Can we give the graviton a mass? Does it even make sense to speak of a massive graviton? In this essay I shall answer these questions in the affirmative. I shall outline an alternative to Einstein Gravity that satisfies the Equivalence Principle and automatically passes all classical weak-field tests (GM/r approx 10^{-6}). It also passes medium-field tests (GM/r approx 1/5), but exhibits radically different strong-field behaviour (GM/r approx 1). Black holes in the usual sense do not exist in this theory, and large-scale cosmology is divorced from the distribution of matter. To do all this we have to sacrifice something: the theory exhibits {*prior geometry*}, and depends on a non-dynamical background metric.
TL;DR: The spectrum and statistics of the cosmic microwave background radiation (CMBR) are investigated under the hypothesis that scale invariance of the primordial density fluctuations should be promoted to full conformal invariance, allowing for deviations from naive scaling as mentioned in this paper.
Abstract: The spectrum and statistics of the cosmic microwave background radiation (CMBR) are investigated under the hypothesis that scale invariance of the primordial density fluctuations should be promoted to full conformal invariance, allowing for deviations from naive scaling. The spectral index of the two-point function of density fluctuations is determined by the trace anomaly to be greater than one, implying less power at large distance scales than a Harrison-Zel’dovich spectrum. Conformal invariance also implies non-Gaussian statistics of the CMBR and determines the large angular dependence of its three-point correlations. [S0031-9007(97)03472-8] PACS numbers: 98.70.Vc, 98.80.Hw With the discovery of the anisotropy in the cosmic microwave background radiation (CMBR) [1], cosmology has accelerated its transition from a field based largely on speculation to one in which observational data can be brought to bear on our understanding of the Universe. The CMBR anisotropy is the most sensitive available probe of the primordial density fluctuations from which the large scale structure of the Universe arose. Since the pioneering work of Harrison and Zel’dovich [2] it has been reasonable to suppose that these primordial fluctuations were generated with a scale invariant spectrum during an early epoch in the history of the Universe at the threshold of its classical evolution. Inflationary models are a particular
TL;DR: In this article, a new class of exact solutions for FRW models was obtained by considering a time dependent displacement field for constant deceleration parameter models of the universe, which is based on Lyra's geometry.
Abstract: FRW models have been studied in the cosmological theory based on Lyra’s geometry. A new class of exact solutions has been obtained by considering a time dependent displacement field for constant deceleration parameter models of the universe.
TL;DR: In this article, the spectrum of relic gravitons in a model of string cosmology is computed and the spectrum reaches its maximum at frequencies accessible to LIGO and VIRGO and it is close to the sensitivity of first generation experiments.
Abstract: We compute the spectrum of relic gravitons in a model of string cosmology. In the low- and in the high-frequency limits we re- produce known results. The full spectrum, however, also displays a series of oscillations which could give a characteristic signature at the planned LIGO/VIRGO detectors. For special values of the parameters of the model the signal reaches its maximum already at frequencies accessible to LIGO and VIRGO and it is close to the sensitivity of first generation experiments.
TL;DR: In this article, the authors consider the general behaviour of cosmologies in Brans-Dicke theory where the dilaton is self-interacting via a potentialV(Φ).
TL;DR: In this paper, exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the cases of non-resonant, modified non-onant and resonant cases are given in terms of H -functions, G-functions and in computable series forms.
Abstract: Nuclear reactions govern major aspects of the chemical evolution of galaxies and stars. Analytic study of the reaction rates and reaction probability integrals is attempted here. Exact expressions for the reaction rates and reaction probability integrals for nuclear reactions in the cases of nonresonant, modified nonresonant, screened nonresonant and resonant cases are given. These are expressed in terms of H-functions, G-functions and in computable series forms. Computational aspects are also discussed.
TL;DR: In this paper, the effect of spatial curvature on the duration of the inflationary era was analyzed in both the Jordan and Einstein frames and it was shown that too much curvature reduces the duration to such an extent that the flatness and horizon problems are not solved.
Abstract: The pre-big-bang cosmology inspired by superstring theories has been suggested as an alternative to slow-roll inflation. We analyze, in both the Jordan and Einstein frames, the effect of spatial curvature on this scenario and show that too much curvature --- of either sign --- reduces the duration of the inflationary era to such an extent that the flatness and horizon problems are not solved. Hence, a fine-tuning of initial conditions is required to obtain enough inflation to solve the cosmological problems.
TL;DR: In this article, the Einstein equation is upgraded to a so-called Einstein Langevin equation, which is computed along the lines of the Feynman-Vernon and Schwinger-Keldysh techniques.
Abstract: We consider the classical stochastic fluctuations of spacetime geometry induced by quantum fluctuations of massless nonconformal matter fields in the early Universe. To this end, we supplement the stress-energy tensor of these fields with a stochastic part, which is computed along the lines of the Feynman-Vernon and Schwinger-Keldysh techniques; the Einstein equation is therefore upgraded to a so-called Einstein-Langevin equation. We consider in some detail the conformal fluctuations of flat spacetime and the fluctuations of the scale factor in a simple cosmological model introduced by Hartle, which consists of a spatially flat isotropic cosmology driven by radiation and dust. @S0556-2821~97!04716-4#
TL;DR: In this paper, it was shown that the universe is very likely to be in the domain of the attraction of the global minimum at the end of inflation at large values of the squark and/or slepton fields.