Showing papers on "Structure formation published in 1995"
TL;DR: In this paper, the authors present a simple quantitative explanation of why galaxies are distributed in a filament-dominated web-like structure, showing that the final-state web is actually present in embryonic form in the overdensity pattern of the initial fluctuations, with nonlinear dynamics just sharpening the image.
Abstract: Observations indicate galaxies are distributed in a filament-dominated web-like structure. Numerical experiments at high and low redshift of viable structure formation theories also show filament-dominance. We present a simple quantitative explanation of why this is so, showing that the final-state web is actually present in embryonic form in the overdensity pattern of the initial fluctuations, with nonlinear dynamics just sharpening the image. The web is largely defined by the position and primordial tidal fields of rare events in the medium, with the strongest filaments between nearby clusters whose tidal tensors are nearly aligned. Applications of the cosmic web theory to observations include probing cluster-cluster bridges by weak gravitational lensing, X-rays, and the Sunyaev-Zeldovich effect and probing high redshift galaxy-galaxy bridges by low column density Lyman alpha absorption lines.
788 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
TL;DR: In this article, the spatial distribution of substructure in clusters of galaxies using Einstein X-ray observations was examined and it was found that subclusters have a markedly anisotropic distribution that reflects the surrounding matter distribution on supercluster scales.
Abstract: We have examined the spatial distribution of substructure in clusters of galaxies using Einstein X-ray observations. Subclusters are found to have a markedly anisotropic distribution that reflects the surrounding matter distribution on supercluster scales. Our results suggest a picture in which cluster formation proceeds by mergers of subclusters along large-scale filaments. The implications of such an anisotropic formation process for the shapes, orientations, and kinematics of clusters are discussed briefly.
115 citations
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.
114 citations
TL;DR: In this article, the effective pair interaction between particles is calculated from the Ornstein-Zernike theory with Percus-Yevick closure to reveal the phenomena of internal particle layering as well as in-layer structure formation.
Abstract: Film stability and structure formation inside a liquid film containing colloidal particles are investigated by Monte Carlo (MC) numerical simulations and by analytical methods. The effective pair interaction between particles is calculated from the Ornstein–Zernike theory with Percus–Yevick closure. Consistent with the recent experimental observations and theoretical studies, these MC simulations reveal the phenomena of internal particle layering as well as inlayer structure formation. In particular, an ordered two‐dimensional hexagonal structure is observed at a particle concentration of 37 vol% (instead of 43 vol% for the hard‐sphere potential) when the effective pair interaction between particles is taken into account. Furthermore, the particles inside a layer ‘‘condense’’ due to the attractive depletion force which leads to the formation of voids. The formation of such void structures results in the formation of ‘‘dark spots’’ which have been observed in film thinning experiments. The calculated film ...
86 citations
TL;DR: In this paper, the cosmological implications of the very existence of these clusters for hierarchical structure formation theories such as standard Omega = 1 CDM (cold dark matter), hybrid Omega = (1 C + HDM), and flat, low-density Lambda + CDM models are discussed.
Abstract: During the course of a gravitational lensing survey of distant, X-ray selected Einstein Observatory Extended Medium Sensitivity Survey (EMSS) clusters of galaxies, we have studied six X-ray-luminous (L(sub x) greater than 5 x 10(exp 44)(h(sub 50)(exp -2))ergs/sec) clusters at redshifts exceeding z = 0.5. All of these clusters are apparently massive. In addition to their high X-ray luminosity, two of the clusters at z approximately 0.6 exhibit gravitationally lensed arcs. Furthermore, the highest redshift cluster in our sample, MS 1054-0321 at z = 0.826, is both extremely X-ray luminous (L(sub 0.3-3.5keV)=9.3 x 10(exp 44)(h(sub 50)(exp -2))ergs/sec) and exceedingly rich with an optical richness comparable to an Abell Richness Class 4 cluster. In this Letter, we discuss the cosmological implications of the very existence of these clusters for hierarchical structure formation theories such as standard Omega = 1 CDM (cold dark matter), hybrid Omega = 1 C + HDM (hot dark matter), and flat, low-density Lambda + CDM models.
70 citations
TL;DR: In this article, the authors compare the observable properties of the galaxy population in popular hierarchical models of galaxy formation and find that although the models have some success in remedying the shortcomings of the standard CDM cosmogony, none of these new models produce broad agreement with the whole range of observations.
Abstract: We predict the observable properties of the galaxy population in popular hierarchical models of galaxy formation. We employ a detailed semianalytic procedure which incorporates the formation and merging of dark matter halos, the shock heating and radiative cooling of gas, self-regulated star formation, the merging of galaxies within dark matter halos, and the spectral evolution of the stellar populations. We contrast the standard CDM cosmogony with variants of the CDM model having either a low value of H_0, or a low value of Omega with or without a cosmological constant. In addition, we compare galaxy formation in these CDM universes with a CHDM model. We find that although the models have some success in remedying the shortcomings of the standard CDM cosmogony, none of these new models produce broad agreement with the whole range of observations. Although the low-Omega and Omega+Lambda=1 CDM models reduce the discrepancy between the predicted and observed Tully-Fisher relations (the main weakness of galaxy formation in standard CDM), these models predict an inverted colour-magnitude relation and do not produce an exponential cut-off at the bright end of the galaxy luminosity function. All of our models predict recent star formation and exhibit galaxy colours bluer than observed, but this problem is far more severe in the CHDM model which produces colours about two magnitudes too blue in B-K. Unlike in the variants of the CDM model in the CHDM case this result is not dependent on our model of stellar feedback, but is instead directly caused by the late epoch of structure formation in this model.
61 citations
TL;DR: In this article, the authors use semi-analytic models of galaxy formation developed by Kauffmann, White and Guiderdoni to generate predictions for the observed properties of cluster and group galaxies at redshifts between 0 and 0.6.
Abstract: We use the semi-analytic models of galaxy formation developed by Kauffmann, White \& Guiderdoni to generate predictions for the observed properties of cluster and group galaxies at redshifts between 0 and 0.6. We examine four sets of cosmological initial conditions: low-density CDM models with and without cosmological constant, a flat CDM model and a mixed dark matter model. These models were selected because they span a wide range in cluster formation epoch. The semi-analytic models that we employ are able to follow both the evolution of the dark matter component of clusters and the formation and evolution of the stellar populations of the cluster galaxies. We are thus able to generate model predictions that can be compared directly with the observational data. In the low-density CDM models, clusters form at high red- shift and accrete very little mass at recent times. Our models predict that essentially no evolution in the observed properties of clusters will have occurred by a redshift of 0.6, in direct contradiction with the data. In contrast, in the MDM model, both galaxies and clusters form extremely late. This model predicts evolution which appears to be too extreme to be in agreement with the observations. The flat CDM model, which is intermediate in structure formation epoch, is most successful. This model is able to account for the evolution of the blue fraction of rich clusters with redshift, the relationship between blue fraction and cluster richness at different epochs, and the changes in the distribution of the morphologies of cluster galaxies by a redshift of 0.4.
55 citations
TL;DR: A range of masses and lifetimes which delay matter--radiation equality and improve the agreement with the data of Cold Dark Matter models with critical density are defined.
Abstract: We consider the effects of a massive, unstable neutrino on the evolution of large-scale structure and anisotropies in the cosmic microwave background. A comparison with large-scale structure data allows us to rule out a wide range of masses and lifetimes for such neutrinos. We also define a range of masses and lifetimes which delay matter-radiation equality and improve the agreement with the data of cold dark matter models with critical density.
50 citations
TL;DR: In this article, the authors reanalyze the PS-formalism by explicitly counting underdense regions which are embedded within overdense regions, so called cloud-in-clouds.
Abstract: The formalism by Press and Schechter (PS) is often used to infer number densities of virialized objects of mass M (e.g. quasars, galaxies, clusters of galaxies, etc.) from a count of initially overdense regions in a Gaussian density perturbation field. We reanalyze the PS-formalism by explicitly counting underdense regions which are embedded within overdense regions, so called cloud-in-clouds. In contrast to the original PS-formalism, our revised analysis automatically accounts for all the cosmic material. We find that mass distribution functions for virialized objects are altered by the proper solution of the cloud-in-cloud problem. These altered distribution functions agree much better with distribution functions inferred form N-body simulations than the original PS-distribution functions.
49 citations
TL;DR: In this article, the light neutrino and the light axino are discussed as possible examples of a working particle physics model. And the authors point out that the increased power at sub-galaxy scale predicted by this scenario could lead to rich subgalaxy structures.
TL;DR: In this paper, the uncertainties in the amplitudes of the spatial correlation functions estimated from angular correlations in a sample from the APM Galaxy Survey, with b_J=17-20, were analyzed.
Abstract: We analyze the uncertainties in the amplitudes of the spatial correlation functions estimated from angular correlations in a sample from the APM Galaxy Survey, with $b_J=17-20$. We model the uncertainties in the selection function and in the evolution of clustering. In particular we estimate $\sigma_8^{APM}$, the rms galaxy number fluctuations in spheres of radius at $8 \Mpc$, from the measured angular variance in the APM. The uncertainty in $\sigma_8^{APM}$ has three main contributions: 8\% from sampling and selection function uncertainties, 7\% from the uncertainty in the evolution of clustering and 3\% from the uncertainty in the value of $\Omega_0$. Including all these contributions, we find $\sigma_8^{APM}$ is in the range $0.78-1.08$. If the galaxy clustering in the APM evolves as expected from gravitational clustering of matter fluctuations, then $\sigma_8^{APM}=0.95 \pm 0.07$ ($1.00 \pm 0.08$) for $\Omega_0 \simeq 1$ ($\Omega_0 \simeq 0$), close to the values for nearby optical samples. On the other hand, if we assume that clustering evolution is fixed in comoving coordinates $\sigma_8^{APM}=0.83 \pm 0.05$ ($0.87 \pm 0.06$), closer to the results for nearby IRAS samples. The final uncertainty in the range of values for the hierarchical amplitudes $S_J\equiv \xibar_J/\xibar_2^{J-1}$ is typically twice the estimated sampling errors, with the highest values for the case of less clustering evolution. We compare our estimates with other results and discuss the implications for models of structure formation.
TL;DR: In this paper, the effects of the Yukawa couplings on the radiative corrections to quark masses were studied and it was shown that b − τ equality at M GUT may still give the correct m b / m τ -ratio at low energies, but only if there is large μ − τ mixing in the charged leptonic sector.
TL;DR: In this paper, the authors used large-scale cosmological simulations to compare the motions of rich clusters of galaxies with the motion of the underlying matter distribution, and they found that these motions can serve as an efficient tool to constrain Cosmological models.
Abstract: Can clusters of galaxies be used to trace the large-scale peculiar velocity field of the universe? We answer this question by using large-scale cosmological simulations to compare the motions of rich clusters of galaxies with the motion of the underlying matter distribution. Three models are investigated: Omega = 1 and Omega = 0.3 cold dark matter (CDM), and Omega = 0.3 primeval baryonic isocurvature (PBI) models, all normalized to the Cosmic Background Explorer (COBE) background fluctuations. We compare the cluster and mass distribution of peculiar velocities, bulk motions, velocity dispersions, and Mach numbers as a function of scale for R greater than or = 50/h Mpc. We also present the large-scale velocity and potential maps of clusters and of the matter. We find that clusters of galaxies trace well the large-scale velocity field and can serve as an efficient tool to constrain cosmological models. The recently reported bulk motion of clusters 689 +/- 178 km/s on approximately 150/h Mpc scale (Lauer & Postman 1994) is larger than expected in any of the models studied (less than or = 190 +/- 78 km/s).
TL;DR: In this article, the formation of large-scale structure arising from COBEnormalized spectra computed by convolving a primordial double-inflation perturbation spectrum with the CDM transfer function was simulated.
Abstract: We have simulated the formation of large-scale structure arising from COBEnormalized spectra computed by convolving a primordial double-inflation perturbation spectrum with the CDM transfer function. Due to the broken scale invariance (’BSI’) characterizing the primordial perturbation spectrum, this model has less small-scale power than the (COBE-normalized) standard CDM model. The particle-mesh code (with 512 3 cells and 256 3 particles) includes a model for thermodynamic evolution of baryons in addition to the usual gravitational dynamics of dark matter. It provides an estimate of the local gas temperature. In particular, our galaxy-finding procedure seeks peaks in the distribution of gas that has cooled. It exploits the fact that “cold” particles trace visible matter better than average and thus provides a natural biasing mechanism. The basic picture of large-scale structure formation in the BSI model is the familiar hierarchical clustering scenario. We obtain particle in cell statistics, the galaxy correlation function, the cluster abundance and the cluster-cluster correlation function and statistics for large and small scale velocity fields. We also report here on a semi-quantitative study of the distribution of gas in different temperature ranges. Based on confrontation with observations and comparison with standard CDM, we conclude that the BSI scenario could represent a promising modification of the CDM picture capable of describing many details of large-scale structure formation.
TL;DR: Several problems in cosmology and astrophysics are described in this paper, in which critical phenomena of various types may play a role, such as the organization of the disks of spiral galaxies, various aspects of the problem of structure formation in icosmology, the selection of initial conditions and parameters in particle physics and cosmology, and recovering the classical limit from nonperturbative formulations of quantum gravity.
Abstract: Several problems in cosmology and astrophysics are described in which critical phenomena of various types may play a role. These include the organization of the disks of spiral galaxies, various aspects of the problem of structure formation in icosmology, the problem of the selection of initial conditions and parameters in particle physics and cosmology and the problem of recovering the classical limit from non-perturbative formulations of quantum gravity.
TL;DR: In this paper, the authors discuss the effects of gravitational collapse on the shape of absorption line profiles for low column density (log N(HI) < 14) Lyman Alpha forest clouds and argue by comparison with cosmological simulations that Lyman alpha forest observations show the signs of ongoing gravitational structure formation at high redshift.
Abstract: We discuss the effects of gravitational collapse on the shape of absorption line profiles for low column density (log N(HI) < 14) Lyman Alpha forest clouds and argue by comparison with cosmological simulations that Lyman alpha forest observations show the signs of ongoing gravitational structure formation at high redshift. The departures of observed line profiles from thermal Voigt profiles (caused by bulk motion of infalling gas and compressional heating) are evident from the results of profile fitting as a correlation in velocity space among pairs of components with discrepant Doppler parameters. This correlation also allows us to qualitatively understand the meaning of the Doppler parameter - column density (b vs. N(HI)) diagram for intergalactic gas.
TL;DR: It is concluded that reliable quantitative predictions must take into account non-Gaussianity, vorticity generation, and nonlinear fragmentation effects of the cosmic string scenario.
Abstract: We develop quantative methods for the study of structure formation with cosmic strings in an expanding universe. The gravitational effects of arbitrary string configurations are calculated using linearized gravity. The growth of density fluctuations is then studied using these gravitational forces as a source term in the Zeldovich approximation. We use either the adhesion modification or an N-body tree code to project this fluctuation growth into the nonlinear regime. These methods are applied to specific loop and long string solutions beginning at equal matter and radiation ${\mathit{t}}_{\mathrm{eq}}$ on scales corresponding to about 10 Mpc today (h=0.5). We reproduce analytic results for spherical and planar collapse. We show that these methods are applicable to accretion about closed oscillating loops and in the wakes of moving long strings which possess significant small-scale structure, quantitatively confirming the wiggly string approximation with a renormalized string energy density \ensuremath{\mu}\ifmmode \tilde{}\else \~{}\fi{}. We demonstrate the efficiency of the fragmentation of wakes created by wiggly strings by the present day. These methods are sufficiently computationally efficient to employ in the study of an evolving string network. For the cosmic string scenario, we conclude that reliable quantitative predictions must take into account non-Gaussianity, vorticity generation, and nonlinear fragmentation effects.
TL;DR: In this article, the authors compute the comoving space densities of quasars and high-redshift galaxies with cosmic string models and compare results with observations and show that the cosmic string model can produce enough high-density objects to account for the observations.
Abstract: The number densities of quasars and high-redshift galaxies introduce strict constraints on theories of large-scale structure formation. We compute the comoving space densities of these objects with cosmic string models and compare results with observations. We show that the cosmic string models can produce enough high-density objects to account for the observations. We also show that, because of non-Gaussian initial conditions, the number density of quasars is higher than expected from conventional Gaussian Press-Schechter analysis. The cosmic string model is consistent with the QSO abundance limit at z = 4.5, both in Ω = 1.0 and in Ω = 0.2 cases. However, there are problems with large-scale structure when the "stringy" power spectrum is compared with the three-dimensional Automatic Plate Measuring Facility (APM) spectrum in Cambridge, England.
01 Jan 1995
TL;DR: In this paper, the place of cosmic strings and other topological defects in modern cosmology is reviewed, particularly focussing on their potential role in large-scale structure formation.
Abstract: The place of cosmic strings and other topological defects in modern cosmology is reviewed, particularly focussing on their potential role in large-scale structure formation. Most emphasis is given to cosmic strings but the cosmological implications of global monopoles and global textures are also summarized. String structure and properties are briefly introduced, before discussing the formation and evolution of a string network in an expanding universe. The gravitational effects of the conical string spacetime are delineated along with potential observational consequences such as gravitational lensing, Doppler effects in the microwave background, and black hole formation. The formalism for calculating gravitational radiation by loops and long strings is presented, leading to a discussion of experimental constraints on the stochastic background predicted by strings. We then consider the present status of the cosmic string scenario for large-scale structure formation presenting normalizations for galactic and CMBR scales. Finally, the properties and evolution of global monopoles and textures are introduced, before discussing their respective gravitational effects and large-scale structure scenarios.
TL;DR: The Sloan Digital Sky Survey (SDSS) as mentioned in this paper provides a complete imaging and spectroscopic survey of the high-latitude northern sky for studying the clustering and large-scale structure of the universe.
Abstract: The Sloan Digital Sky Survey (SDSS) will provide a complete imaging and spectroscopic survey of the high-latitude northern sky. The 2D survey will image the sky in five colors and will contain nearly 5 x 107 galaxies to g ~ 23m. The spectroscopic survey will obtain spectra of the brightest 106 galaxies, 105 quasars, and 103.5 rich clusters of galaxies (to g~18.3-19.3m, respectively). I summarize some of the science opportunities that will be made possible by this survey for studying the clustering and large-scale structure of the universe.
The survey will identify a complete sample of several thousand rich clusters of galaxies, both in 2D and 3D - the largest automated sample yet available. The extensive cluster sample can be used to determine critical clustering properties such as the luminosity-function, velocity-function, and mass-function of clusters of galaxies (a critical test for cosmological models), detailed cluster dynamics and W(dyn), the cluster correlation function and its dependence on richness, cluster evolution, superclustering and voids to the largest scales yet observed, the motions of clusters and their large-scale peculiar velocity field, as well as detailed correlations between x-ray and optical properties of clusters, the density-morphology relation, and cluster-quasar associations. The large redshift survey, reaching to a depth of 600h-1 Mpc, will accurately map the largest scales yet observed, determine the power-spectrum and correlation function on these large scales for different type galaxies, and study the clustering of quasars to high redshifts (z 4). The implications of the survey for cosmological models, the dark matter, and W are also discussed.
TL;DR: In this article, a systematic investigation of the individual mechanisms for anisotropy formation based on elementary gravitational and fluid dynamics is presented, and the full physical content and detailed structure of anisotropies can be understood in a simple and intuitive fashion.
Abstract: Cosmic microwave background anisotropies provide a vast amount of information on both structure formation in the universe and the background dynamics and geometry. The full physical content and detailed structure of anisotropies can be understood in a simple and intuitive fashion through a systematic investigation of the individual mechanisms for anisotropy formation, based on elementary gravitational and fluid dynamics.
TL;DR: In this paper, the predicted level of anisotropies is a function of Omega(sub 0) and the ratio of the density in ionized baryons to the critical density and is shown to depend strongly on the large and small-scale power.
Abstract: If the universe was reionized at high reshift (z greater than or approximately equal to 30) or never recombined, then photon-electron scattering can erase fluctuations in the cosmic microwave background at scales less than or approximately equal to 1 deg. Peculiar motion at the surface of last scattering will then have given rise to new anisotropy at the 1 min level through the Vishniac effect. Here the observed fluctuations in galaxy counts are extrapolated to high redshifts using linear theory, and the expected anisotropy is computed. The predicted level of anisotropies is a function of Omega(sub 0) and the ratio of the density in ionized baryons to the critical density and is shown to depend strongly on the large- and small-scale power. It is not possible to make general statements about the viability of all reionized models based on current observations, but it is possible to rule out specific models for structure formation, particularly those with high baryonic content or small-scale power. The induced fluctuations are shown to scale with cosmological parameters and optical depth.
TL;DR: A partially new, fully local and gauge invariant system of perturbation equations is presented to treat microwave background and dark matter fluctuations induced by topological defects to show that this treatment is extremly well suited for linear numerical analysis of structure formation.
Abstract: The topic of this letter is structure formation with topological defects. We first present a partially new, fully local and gauge invariant system of perturbation equations to treat microwave background and dark matter fluctuations induced by topological defects (or any other type of seeds). We show that this treatment is extremly well suited for linear numerical analysis of structure formation by applying it to the texture scenario. Our numerical results cover a larger dynamical range than previous investigations and are complementary since we use substantially different methods.
01 Jan 1995
TL;DR: In this paper, the authors present results of N-body simulations, including effects of cooling and heating due to the background ionizing flux, aimed at modelling space distribution of the Lyα absorbers in the context of cosmological structure formation.
Abstract: We present results of N-body simulations, including effects of cooling and heating due to the background ionizing flux, aimed at modelling space distribution of the Lyα absorbers in the context of cosmological structure formation. The observed z-dependence of the number of Lyα lines per unit redshift is reproduced by the model within the uncertainties. The sharp decrease with time in the number density at high redshift is mainly due to the formation of structures whereas Lyα gas survives at low redshift because of the decreasing ionizing flux.
TL;DR: The power spectrum of density perturbations for two class of models: one in which all the dark matter is non baryonic (CDM) and one inWhich it is all baryonics (BDM) are calculated.
Abstract: We study the effects of cosmic strings on structure formation in open universes. We calculate the power spectrum of density perturbations for two class of models: one in which all the dark matter is non baryonic (CDM) and one in which it is all baryonic (BDM). Our results are compared to the 1 in 6 IRAS QDOT power spectrum. The best candidates are then used to estimate $\mu$, the energy per unit length of the string network. Some comments are made on mechanisms by which structures are formed in the two theories.
TL;DR: The cold dark matter models of structure formation motivated by inflation are holding up well as the observational tests become sharper, providing an important window on the earliest moments and fundamental physics as mentioned in this paper.
Abstract: Alan Guth introduced cosmologists to inflation at the 1980 Texas Symposium. Since, inflation has had almost as much impact on cosmology as the big-bang model itself. However, unlike the big-bang model, it has little observational support. Hopefully, that situation is about to change as a variety and abundance of data begin to test inflation in a significant way. The observations that are putting inflation to test involve the formation of structure in the Universe, especially measurements of the anisotropy of the cosmic background radiation. The cold dark matter models of structure formation motivated by inflation are holding up well as the observational tests become sharper. In the next decade inflation will be tested even more significantly, with more precise measurements of CBR anisotropy, the mean density of the Universe, the Hubble constant, and the distribution of matter, as well as sensitive searches for the nonbaryonic dark matter predicted to exist by inflation. As an optimist I believe that we may be well on our way to a standard cosmology that includes inflation and extends back to around 10^{-32} sec, providing an important window on the earliest moments and fundamental physics.
01 Jan 1995
TL;DR: In this paper, the authors describe how to compute density fluctuations and cosmic microwave anisotropies arising from inflation, and compare these results with the latest cosmological observations using powerful Hamilton-Jacobi methods.
Abstract: Cosmological inflation provides the simplest and most promising mechanism for generating fluctuations for structure formation. Using powerful Hamilton-Jacobi methods, I will describe (1) how to compute density fluctuations and cosmic microwave anisotropies arising from inflation, and (2) improvements of the Zel’dovich approximation describing gravitational collapse. I compare these results with the latest cosmological observations.
01 Jul 1995
TL;DR: In this article, conditions for the establishment of small density perturbations in a self-gravitating two component fluid mixture are studied using a dynamical system approach, and it is shown that besides the existence of exponentially growing and decaying modes, which are present for values of the perturbation wave-number k smaller than a critical value k M, two other, pure oscillatory, modes exist at all scales.
Abstract: Conditions for the establishment of small density perturbations in a self-gravitating two component fluid mixture are studied using a dynamical system approach. It is shown that besides the existence of exponentially growing and decaying modes, which are present for values of the perturbation wave-number k smaller than a critical value k M , two other, pure oscillatory, modes exist at all scales. For k < k M , the growing mode always affects both components of the fluid and not only one of them. Due to the existence of a resonance between the baryonic and the dark perturbations, it is shown that the onset of structure formation in the post recombination epoch is substantially enhanced in a narrow scale band around another critical value kc. For dark matter particles having a mass ∼ 30 eV, the corresponding critical mass scale for the establishment of density perturbations at the time of recombination is of the same order of magnitude as the galactic one.