Showing papers on "Cosmology published in 1995"
Book•
01 May 1995
TL;DR: In this paper, the Friedmann model is used to model the evolution of the Hot Big Bang and its phase transitions and inflation, as well as the Hadron and Lepton Eras and the Plasma Era.
Abstract: PART I: Cosmological Methods The Relativistic Universe The Friedmann Models Alternative Cosmologies: Past and Present Observational Properties of the Universe. PART II: Evolution of the Big Bang Model Physical Properties of the Hot Big Bang The Big Bang and Quantum Gravity Phase Transitions and Inflation The Hadron and Lepton Eras The Plasma Era. PART III: Structure Formation by Gravitational Instability Introduction to Jeans Jeans Instability in Friedmann Models The Origin of Structure I: Baryons Only The Origin of Structure II: Non-Baryonic Matter Cosmological Perturbations Non-Linear Evolution of Perturbations. PART IV: Observational Test Statistics of Galaxy Clustering The Cosmic Microwave Background Peculiar Motions of Galaxies The Post-Recombination Universe.
422 citations
TL;DR: In this article, it was shown that the mass and mass accretion rates of radio-loud and radio-quiet active galactic nuclei are not greatly different, and that the difference between the two classes is associated with the spin of the black hole.
Abstract: The recent development of unified theories of active galactic nuclei (AGNs) has indicated that there are two physically distinct classes of these objects--radio-loud and radio-quiet. Despite differences, the (probable) thermal emissions from the AGNs (continua and lines from X-ray to infrared wavelengths) are quite similar to the two classes of object. We argue that this last result suggests that the black hole masses and mass accretion rates in the two classes are not greatly different, and that the difference between the classes is associated with the spin of the black hole. We assume that the normal process of accretion through a disk does not lead to rapidly spinning holes and propose that galaxies (e.g., spirals) which have not suffered a recent major merger event contain nonrotating or only slowly rotating black holes. When two such galaxies merge, the two black holes are known to form a binary and we assume that they eventually coalesce. The ratio of the number of radio-loud to radio-quiet AGNs at a given thermal (e.g., optical) luminosity is determined by the galaxy merger rate. Comparisons between the predicted and observed radio luminosity functions constrain the efficiencies with which jet power is extracted from the spinning hole and radio emission is produced by the jet.
379 citations
TL;DR: The picture that has emerged from this line of development is that a small closed universe can spontaneously nucleate out of nothing, where by ‘nothing’ I mean a state with no classical space and time.
Abstract: If the cosmological evolution is followed back in time, we come to the initial singularity where the classical equations of general relativity break down. This led many people to believe that in order to understand what actually happened at the origin of the universe, we should treat the universe quantum-mechanically and describe it by a wave function rather than by a classical spacetime. This quantum approach to cosmology was initiated by DeWitt [1] and Misner [2], and after a somewhat slow start has become very popular in the last decade or so. The picture that has emerged from this line of development [3, 4, 6, 5, 7, 8, 9] is that a small closed universe can spontaneously nucleate out of nothing, where by ‘nothing’ I mean a state with no classical space and time. The cosmological wave function can be used to calculate the probability distribution for the initial configurations of the nucleating universes. Once the universe nucleated, it is expected to go through a period of inflation, which is a rapid (quasi-exponential) expansion driven by the energy of a false vacuum. The vacuum energy is eventually thermalized, inflation ends, and from then on the universe follows the standard hot cosmological scenario. Inflation is a necessary ingredient in this kind of scheme, since it gives the only way to get from the tiny nucleated universe to the large universe we live in today.
347 citations
TL;DR: The agreement between the predicted and observed abundances of deuterium, helium-3, helium -4, and lithium-7 confirms the standard cosmology model and allows accurate determination of the baryon density, which is pivotal to the establishment of two dark-matter problems.
Abstract: For almost 30 years, the predictions of big-bang nucleosynthesis have been used to test the big-bang model to within a fraction of a second of the bang. The agreement between the predicted and observed abundances of deuterium, helium-3, helium-4, and lithium-7 confirms the standard cosmology model and allows accurate determination of the baryon density, between 1.7 x 10(-31) and 4.1 x 10(-31) grams per cubic centimeter (corresponding to about 1 to 15 percent of the critical density). This measurement of the density of ordinary matter is pivotal to the establishment of two dark-matter problems: (i) most of the baryons are dark, and (ii) if the total mass density is greater than about 15 percent of the critical density, as many determinations indicate, the bulk of the dark matter must be "non-baryonic," composed of elementary particles left from the earliest moments.
329 citations
TL;DR: In this article, the early formation of bound objects with masses comparable to the cosmological Jeans mass (10^5 solar masses) was investigated by following the growth of isolated spherically symmetric density peaks starting from the linear perturbative regime.
Abstract: We investigate the early formation of bound objects with masses comparable to the cosmological Jeans mass (10^5 solar masses). We follow the growth of isolated spherically symmetric density peaks starting from the linear perturbative regime. The initial parameters correspond to density peaks of various widths and heights in a Cold Dark Matter cosmology. We use a one-dimensional spherical Lagrangian hydrodynamics code to follow the dynamical, thermal, and non-equilibrium chemical evolution of the gas. The system includes a collisionless dark matter component and a baryonic component composed of the nine species H, H^-, H^+, He, He^+, He^{++}, H_2, H_2^+, and e^-. All relevant chemical reactions between these species and their cooling mechanisms are included in the calculations. We find that radiative cooling by H_2 affects the collapse dynamics of the gas only after it has already virialized and become part of the bound object. Therefore, radiative cooling is unlikely to have triggered the initial collapse of perturbations at redshifts z>10. Nevertheless, objects with baryonic masses well below the linear-theory Jeans mass (<10^3 solar masses) collapse due to shell crossing by the dark matter. Such objects could be the progenitors of a primordial population of high-mass stars in the intergalactic medium.
266 citations
TL;DR: In this article, the authors present clustering measurements for samples of galaxies selected by morphological type and luminosity from the recently completed Stromlo-APM Redshift Survey.
Abstract: We present clustering measurements for samples of galaxies selected by morphological type and luminosity from the recently completed Stromlo-APM Redshift Survey. Early type galaxies are clustered more strongly by a factor 3.5--5.5, than late type galaxies. Low-luminosity galaxies are clustered more weakly by a factor of $\sim 2$ than $L^*$ and brighter galaxies on scales $\simgt 1\hMpc$. Also the slope of the correlation function is steeper for low-luminosity galaxies, so that the amplitude is a factor 4 lower at $ 10 \hMpc$. No difference, however, is seen between the clustering of $L^*$ and more luminous galaxies, an observation which may be hard to reconcile with some theories of biased galaxy formation. Both redshift-space and real-space clustering estimates show a similar dependence on luminosity.
258 citations
TL;DR: In this paper, it was shown that seeds for quasar black holes could have originated from the initial cosmological collapse of overdense regions with unusually small rotation, and the gas in these rare regions collapsed into a compact disk that shrinks on a short viscous time scale.
Abstract: We show that seeds for quasar black holes could have originated from the initial cosmological collapse of overdense regions with unusually small rotation. The gas in these rare regions collapses into a compact disk that shrinks on a short viscous time scale. Using an analytical model, we calculate the low-spin tail of the probability distribution of angular momenta for objects that collapse out of a Gaussian random field of initial density perturbations. The population of low-spin systems is significant for any viable power spectrum of primordial density perturbations. Most objects form just above the cosmological Jeans mass (\sim 10^5 M_sun) at high redshifts z>10. In the standard cold dark matter cosmology, the comoving density of 10^{6-7} M_sun objects with viscous evolution times shorter than 10^{6-7} years is about 10^{-3} (h/0.5)^3 Mpc^{-3}, comparable to the local density of bright galaxies. The seed black holes tend to reside within larger mass systems that collapse later and supply the gas needed for the bright quasar activity.
170 citations
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TL;DR: It is shown that string theory has two generic types of domain walls which could be the seeds for inflation, and it is argued that modular physics provides a very robust model of inflation.
Abstract: An exploratory study of the cosmology of moduli in string theory Moduli are argued to be natural inflaton fields and lead to a robust inflationary cosmology in which inflation takes place at the top of domain walls The amplitude of microwave background fluctuations constrains the dynamics responsible for inflation to take place at a higher scale than supersymmetry breaking Models explaining this difference in scales and also preventing the dilaton from running to infinity are proposed The problem of dilaton domination of the energy density of the universe is not resolved
161 citations
TL;DR: In this article, the authors consider a one-parameter family of WDM models and compare the linear power spectra of these models with the corresponding spectra for cold dark matter, hot dark matter and mixed dark matter.
Abstract: Warm dark matter (WDM) is an intriguing model of structure formation from the point of view of both cosmology and particle physics. We consider a one-parameter family of WDM models. The linear power spectra for these models is calculated and compared with the corresponding spectra for cold dark matter (CDM), hot dark matter (HDM) and mixed dark matter (MDM) as well as the power spectrum derived from observations. Our linear analyses suggest that a model universe dominated by a particle whose mass to temperature ratio $m_x/T_x$ is increased by a factor of two as compared with the standard HDM neutrino gives a reasonable fit to the data on large $(>8h^{-1} {\rm ~Mpc})$ scales. $N$-body simulations for this particular WDM model show features of both HDM and CDM. As in HDM, the first objects to collapse are large pancake-like structures. The final matter distribution is rather smooth and structures as small as galaxy halos are excluded. However, there appear to be virialized rich clusters evident in the CDM but not the HDM simulations. Unfortunately, a simple comparison of the matter distribution and its statistical properties with observations indicates that WDM, like CDM, has too much power at small scales. This is particularly evident in the small-scale pairwize velocity dispersion. The cluster multiplicity function has the wrong shape with too many rich clusters being produced, though this conclusion is based on the simple assumption that light traces mass in groups of galaxies.
157 citations
148 citations
TL;DR: In this paper, it was shown that even one 2.4 eV neutrino raises serious difficulties for low-flat CDM models, but only if the Hubble parameter h 0.5.
Abstract: Cold + hot dark matter (CHDM) =1 cosmological models require a total neutrino mass 5 eV. Because recent data support the oscillation explanation of the cosmic ray deficit, which requires that m()m(), this suggests that m()m()2.4 eV. The linear calculations and N-body simulation reported here indicate that an =1 CHDM model with two 2.4 eV neutrinos (designated C2DM) agrees remarkably well with all available observations, but only if the Hubble parameter h0.5. We also show that even one 2.4 eV neutrino raises serious difficulties for low- flat CDM models. © 1995 The American Physical Society.
TL;DR: Analysis of all of the published detections suggests the existence of a peak on degree scales with a height 2.4 to 10 times the amplitude of the power spectrum at large angular scales, which implies that the universe did in fact recombine, and limits theories of structure formation.
Abstract: Fluctuations in the temperature of the cosmic microwave background have now been detected over a wide range of angular scales, and a consistent picture seems to be emerging. This article describes some of the implications for cosmology. Analysis of all of the published detections suggests the existence of a peak on degree scales with a height 2.4 to 10 (90 percent confidence level) times the amplitude of the power spectrum at large angular scales. This result confirms an early prediction, implies that the universe did in fact recombine, and limits theories of structure formation. Illustrative examples show how comparison of the microwave background data and the large-scale structure data will be a potentially powerful means of answering fundamental questions about the universe.
TL;DR: It is shown that in a postinflationary universe minima of the effective potential with a negative cosmological constant are not stationary points of the classical equations of scalar field cosmology, which implies that supersymmetry must be broken in any sensible inflationary cosmology.
Abstract: We review scenarios that have been proposed to solve the cosmological problem caused by moduli in string theory, the postmodern Polonyi problem (PPP). In particular, we discuss the difficulties encountered by the apparently ``trivial'' solution of this problem, in which moduli masses are assumed to arise from nonperturbative, SUSY-preserving, dynamics at a scale higher than that of SUSY breaking. This suggests a powerful cosmological vacuum selection principle in superstring theory. However, we argue that if one eschews the possibility of cancellations between different exponentials of the inverse string coupling, the mechanism described above cannot stabilize the dilaton. Thus, even if supersymmetric dynamics gives mass to the other moduli in string theory, the dilaton mass must be generated by SUSY breaking, and dilaton domination of the energy density of the Universe cannot be avoided. We conclude that the only proposal for solving the PPP that works is the intermediate scale inflation scenario of Randall and Thomas. However, we point out that all extant models have ignored unavoidably large inhomogeneities in the cosmological moduli density at very early times, and speculate that the effects associated with nonlinear gravitational collapse of these inhomogeneities may serve as an efficient mechanism for converting moduli into ordinary matter. As an important by-product of this investigation we show that in a postinflationary universe minima of the effective potential with a negative cosmological constant are not stationary points of the classical equations of scalar field cosmology. Instead, such points lead to catastrophic gravitational collapse of that part of the Universe which is attracted to them. Thus postinflationary cosmology dynamically chooses non-negative values of the cosmological constant. This implies that supersymmetry must be broken in any sensible inflationary cosmology. We suggest that further study of the cosmology of moduli will lead to additional important insight about cosmology, SUSY breaking, and the choice of the vacuum in superstring theory.
TL;DR: If the coherent Higgs oscillations did not decay they could explain the missing mass problem of cosmology and the particle physics parameter \ensuremath{\lambda} is not fine-tuned as usual in order to predict acceptable values of reheating temperature and density and gravitational wave perturbations.
Abstract: We investigate the cosmological consequences of a theory of induced gravity in which the scalar field is identified with the Higgs field of the first symmetry breaking of a minimal SU(5) GUT. The mass of the X boson determines a great value for the coupling constant of of gravity-particle physics. Because of this fact, a ``slow'' rollover dynamics for the Higgs field is not possible in a ``new'' inflation scenario and, moreover, a contraction era for the scale factor in the early Universe exists, after which inflation follows automatically; ``chaotic'' inflation is performed without problems. Inflation is successfully achieved due to the relationship among the masses of particle physics at that scale: the Higgs-boson, X-boson, and Planck masses. As a result the particle physics parameter \ensuremath{\lambda} is not fine-tuned as usual in order to predict acceptable values of reheating temperature and density and gravitational wave perturbations. Moreover, if the coherent Higgs oscillations did not decay they could explain the missing mass problem of cosmology.
TL;DR: In this article, a sustained debate between two philosophers, William Lane Craig and Quentin Smith, who defend opposing positions on the Big Bang has no cause has been conducted, with each chapter being either a criticism of a preceding chapter or being criticized by a subsequent chapter.
Abstract: Contemporary science presents us with the remarkable theory that the universe began to exist about fifteen billion years ago with a cataclysmic explosion called 'the Big Bang'. The question of whether Big Bang cosmology supports theism or atheism has long been a matter of discussion among the general public and in popular science books, but has received scant attention from philosophers. This book sets out to fill this gap by means of a sustained debate between two philosophers, William Lane Craig and Quentin Smith, who defend opposing positions. Craig argues that the Big Bang that began the universe was created by God, while Smith argues that the Big Bang has no cause. The book consists of alternating chapters by Craig and Smith, with each chapter being either a criticism of a preceding chapter or being criticized by a subsequent chapter. Part One consists of Craig's arguments that the past is necessarily finite and that God created the Big Bang, and Smith's criticisms of these arguments. Part Two presents Smith's arguments that Big Bang cosmology is inconsistent with theism and Craig's criticisms of Smith's argument. The authors' arguments are based on Einstein's theory of relativity, and there is also a discussion of Stephen Hawking's new quantum cosmology.
TL;DR: In this article, the authors derived from first principles the equations governing anisotropies, focusing on the interactions of photons with electrons, and showed quantitatively how the signal in several experiments depends on the ionization history.
Abstract: Early reionization changes the pattern of anisotropies expected in the cosmic microwave backgrond. To explore these changes, we derive from first principles the equations governing anisotropies, focusing on the interactions of photons with electrons. Vishniac (1987) claimed that second-order terms can be large in a reionized universe, so we derive equations correct to second order in the perturbations. There are many more second-order terms than were considered by Vishniac. To understand the basic physics involved, we present a simple analytic approximation to the first-order equation. Then, turning to the second order equation, we show that the Vishniac term is indeed the only important one. We also present numerical results for a variety of ionization histories (in a standard cold dark matter universe) and show quantitatively how the signal in several experiments depends on the ionization history. The most pronounced indication of a reionized universe would be seen in very small scale experiments; the expected signal in the Owens Valley experiment is smaller by a factor of order 10 if the last scattering surface is at a redshift z approximately = 100 as it would be if the universe were reionized very early. On slightly larger scales, the expected signal in a reionized universe is smaller than it would be with standard recombination, but only a factor of 2 or so. The signal is even smaller in these experiments in the intermediate case where some photons last scattered at the standard recombination epoch.
Posted Content•
TL;DR: An introduction to modern theories for the origin of structure in the universe is given in this article, followed by a brief review of the growth of cosmological perturbations in an expanding universe and a summary of some important observational results.
Abstract: An introduction to modern theories for the origin of structure in the Universe is given. After a brief review of the growth of cosmological perturbations in an expanding Universe and a summary of some important observational results, the lectures focus on the inflationary Universe scenario and on topological defect models of structure formation. A summary of the theory and current observational status of cosmic microwave background temperature fluctuations is given. The final chapter is devoted to some speculative ideas concerning the connection between cosmology and fundamental physics, in particular to ways in which the singularity problem of classical cosmology may be resolved.
TL;DR: It is shown that the Hubble constant is affected by non-trivial scale dependent shear terms, while the spatial anisotropy of the metric influences significantly the scale-dependence of the matter distribution.
Abstract: We discuss the averaging hypothesis tacitly assumed in standard cosmology. Our approach is implemented in a "3+1" formalism and invokes the coarse graining arguments, provided and supported by the real-space Renormalization Group (RG) methods. Block variables are introduced and the recursion relations written down explicitly enabling us to characterize the corresponding RG flow. To leading order, the RG flow is provided by the Ricci-Hamilton equations studied in connection with the geometry of three-manifolds. The properties of the Ricci-Hamilton flow make it possible to study a critical behaviour of cosmological models. This criticality is discussed and it is argued that it may be related to the formation of sheet-like structures in the universe. We provide an explicit expression for the renormalized Hubble constant and for the scale dependence of the matter distribution. It is shown that the Hubble constant is affected by non-trivial scale dependent shear terms, while the spatial anisotropy of the metric influences significantly the scale-dependence of the matter distribution.
TL;DR: In this article, the authors investigate the light gravitino regeneration rate in the early Universe in models based on $N=1$ supergravity. But they do not consider the effect of temperature on the regeneration rate.
Abstract: We investigate the light gravitino regeneration rate in the early Universe in models based on $N=1$ supergravity. Motivated by a recent claim by Fischler, we evaluate finite-temperature effects on the gravitino regeneration rate due to the hot primordial plasma for a wide range of the supersymmetry-breaking scale $F$. We find that thermal corrections to the gravitino pole mass and to the Goldstino coupling are negligible for a wide range of temperatures, thereby justifying the extension of the equivalence theorem for the helicity-1/2 gravitino and Goldstino to a hot primordial plasma background. Utilizing the Braaten-Pisarski resummation method, the helicity-1/2 gravitino regeneration rate is found to be $0.25 \alpha_s(T) \log(1/\alpha_s(T))|{m_{\rm soft}/F}|^2 T^3(1 + \alpha_s(T) \log(1/\alpha_s(T)) + T^2 / |F|)$ up to a calculable, model-dependent ${\cal O}(1)$ numerical factor. We review the implications of this regeneration rate for supergravity cosmology, focusing in particular on scenaria for baryogenesis.
Posted Content•
03 Apr 1995
TL;DR: In this article, a set of lecture notes basd on the lectures on cosmological dynamics given by E Bertschinger at Les Houches in August 1993 are described. The contents include elementary mechanics in cosmology, Eulerian and Lagrangian fluid dynamics, hot dark matter, and relativistic cosmology perturbation theory.
Abstract: This is a set of lecture notes basd on the lectures on cosmological dynamics given by E Bertschinger at Les Houches in August 1993 The contents include elementary mechanics in cosmology, Eulerian and Lagrangian fluid dynamics, hot dark matter, and relativistic cosmological perturbation theory To typeset the notes one must first obtain the style files and figures in file figmacuu sent separately Place all the files in one directory, run latex three times, and run dvips or equivalent to produce a postscript file
TL;DR: The case is made here for a Hubble Constant that is even smaller than the lower bound of the accepted range on the basis of the great advantages, all theoretical in nature, of a Hubble constant of around 30 kilometers per second per megaparsec.
Abstract: Although recent determinations of the distance to the Virgo cluster based on Cepheid
variable stars represent an important step in pinning down the Hubble constant, after 65
years a definitive determination of the Hubble constant still eludes cosmologists. At
present, most of the observational determinations place the Hubble constant between 40 and
90 kilometers per second per megaparsec (km s–1 Mpc–1).
The case is made here for a Hubble constant that is even smaller than the lower bound of
the accepted range on the basis of the great advantages, all theoretical in nature, of a
Hubble constant of around 30 kilometers per second per megaparsec. Such a value for the
Hubble cures all of the ills of the current theoretical orthodoxy, that is, a spatially
flat universe composed predominantly of cold dark matter.
TL;DR: In this article, the authors report on Keck observations and confirm the redshift of the most distant galaxy known: 8C1435+63 at z = 4.25.
Abstract: We report on Keck observations and confirm the redshift of the most distant galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly$\\alpha$ line, a Ly$\\alpha$ forest continuum break and a continuum break at $\\lambda_{rest}=912$\\AA. The Ly$\\alpha$ emission is spatially extended and roughly aligned with the radio source. The galaxy shows a double structure in the $I$-band ($\\lambda_{rest}\\approx$1500\\AA) which is aligned with the radio axis; the two $I$-band components spatially coincide with the nuclear and southern radio components. Some fraction of the $I$ band emission could be due to a nonthermal process such as inverse compton scattering. In the $K$-band ($\\lambda_{rest}\\approx$4200\\AA), which may be dominated by starlight, the galaxy has a very low surface brightness, diffuse morphology. The $K$ morphology shows little relationship to the radio source structure, although the major axis of the $K$ emission is elongated roughly in the direction of the radio source axis. The galaxian continuum is very red ($I-K>4$) and if the $K$ continuum is due to starlight, implies a formation redshift of $z_f > 5$. We speculate that this galaxy may be the progenitor of a present day cD galaxy.
TL;DR: In this article, the two distinct irreversible phenomena of matter creation and bulk viscosity are considered as independent, giving cross effects in relativistic extended irreversible thermodynamics, as applied to the primordial Friedman-Lemaitre-Robertson-Walker cosmology.
TL;DR: In this paper, a number of steady-state drift-dominated modulation models have been developed by the Potchefstroom modulation group and a review of these models is discussed and briefly compared.
Abstract: A number of steady-state drift-dominated modulation models has been developed by the Potchefstroom modulation group. In this review a selection of these models is discussed and briefly compared. A short overview of the relevant drift theory incorporated into the models is also given.
TL;DR: In this paper, the coupling between the cosmic microwave background radiation (CMBR) and the primordial magnetic field can resonantly convert the photons into gravitons, which induces a frequency-independent fluctuation in the photon flux.
Abstract: We point out that the coupling between the cosmic microwave background radiation (CMBR) and the primordial magnetic field can resonantly convert the photons into gravitons, which induces a frequency-independent fluctuation in the photon flux. Using the observed CMBR fluctuation, we derive a bound on the primordial field strength. The effect can also convert the relic gravitons into photons. For the non-string-based inflation theories it provides a direct test via measurement of long-wavelength electromagnetic waves. For the string cosmology it gives a new bound on the Hubble parameter at the big bang.
Book•
01 Jan 1995
TL;DR: The cosmological framework of the high-redshift universe has been studied in this paper, where it is shown that galaxies and dark matter can be represented by quasars and their demography.
Abstract: Preface 1. The cosmological framework 2. Galaxies and dark matter 3. Emergence of cosmic structure 4. Quasars and their demography 5. Some probes and relics of the high-redshift universe 6. Some fundamental questions References Some further reading Author index Subject index.