QUASARS AND LARGE SCALE STRUCTURE OF THE UNIVERSE

The majority of bright distant quasars $(z {}^{>}_{\sim} 1)$ may form in massive mergers appearing in compact galaxy groups in/and young clusters. The expected tests are (i) large correlation signal for medium-$z$ QSOs $(1 < z < 2)$ and (ii) direct search for quasar groups (QGs) indicating positions of distant pre-superclusters which later will evolve to the "systems" like the local Great Attractor or Shapley concentration. We discuss large QGs with more than ten members within regions $\le l_{LS} \sim 100-150 \, h^{-1} Mpc$, tracing the enhanced density regions at $z {}^{<}_{\sim} 2$. These early large scale structures (i) provide a natural way to "bias" the distribution of Abell clusters, and (ii) suggest that the spectrum of primordial density perturbations is nearly flat at scales encompassing both cluster and GAs, $l = \pi k^{-1} \in(10,100)h^{-1} Mpc: \Delta^{2}_{k} \sim k^{3}P(k) \sim k^{\gamma}, \gamma = 1^{+0.6}_{-0.4}$.Comment: 5 pages, uuencoded Z-compressed postscript, contribution to the Proceedings of Rencontres de Moriond 1995 "Clustering in the Universe

Breakdown of Semiclassical Methods in de Sitter Space

Massless interacting scalar fields in de Sitter space have long been known to experience large fluctuations over length scales larger than Hubble distances. A similar situation arises in condensed matter physics in the vicinity of a critical point, and in this better-understood situation these large fluctuations indicate the failure in this regime of mean-field methods. We argue that for non-Goldstone scalars in de Sitter space, these fluctuations can also be interpreted as signaling the complete breakdown of the semi-classical methods widely used throughout cosmology. By power-counting the infrared properties of Feynman graphs in de Sitter space we find that for a massive scalar interacting through a \lambda \phi^4$ interaction, control over the loop approximation is lost for masses smaller than m \simeq \sqrt \lambda H/2\pi, where H is the Hubble scale. We briefly discuss some potential implications for inflationary cosmology.Comment: 24 pages, 7 figures, v2; added references, clarified the resummation discussio

A note on second-order perturbations of non-canonical scalar fields

We study second-order perturbations for a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. By employing different approaches to cosmological perturbation theory, we show that, even in this simplified set-up, the second-order perturbations to the stress tensor, the energy density and the pressure display potential instabilities, which are not present at linear order. The conditions on the Lagrangian under which these instabilities take place are provided. We also discuss briefly the significance of our analysis in light of the possible linearization instability of these fields about the FRW background.Comment: 8 page, Revtex 4. Clarifications added, results unchanged; [v3] 10 pages, matches with the published version, Discussion for specific cases expanded and preliminary results including the metric perturbations discusse

Second-order corrections to noncommutative spacetime inflation

We investigate how the uncertainty of noncommutative spacetime affects on inflation. For this purpose, the noncommutative parameter $\mu_0$ is taken to be a zeroth order slow-roll parameter. We calculate the noncommutative power spectrum up to second order using the slow-roll expansion. We find corrections arisen from a change of the pivot scale and the presence of a variable noncommutative parameter, when comparing with the commutative power spectrum. The power-law inflation is chosen to obtain explicit forms for the power spectrum, spectral index, and running spectral index. In cases of the power spectrum and spectral index, the noncommutative effect of higher-order corrections compensates for a loss of higher-order corrections in the commutative case. However, for the running spectral index, all higher-order corrections to the commutative case always provide negative spectral indexes, which could explain the recent WMAP data.Comment: 15 pages, no figure, version published in PR

Super-Hubble de Sitter Fluctuations and the Dynamical RG

Perturbative corrections to correlation functions for interacting theories in de Sitter spacetime often grow secularly with time, due to the properties of fluctuations on super-Hubble scales. This growth can lead to a breakdown of perturbation theory at late times. We argue that Dynamical Renormalization Group (DRG) techniques provide a convenient framework for interpreting and resumming these secularly growing terms. In the case of a massless scalar field in de Sitter with quartic self-interaction, the resummed result is also less singular in the infrared, in precisely the manner expected if a dynamical mass is generated. We compare this improved infrared behavior with large-N expansions when applicable.Comment: 33 pages, 4 figure

The General Solution of Bianchi Type VIIhVII_h Vacuum Cosmology

The theory of symmetries of systems of coupled, ordinary differential equations (ODE) is used to develop a concise algorithm in order to obtain the entire space of solutions to vacuum Bianchi Einstein Field Equations (EFEs). The symmetries used are the well known automorphisms of the Lie algebra for the corresponding isometry group of each Bianchi Type, as well as the scaling and the time re-parametrization symmetry. The application of the method to Type VII_h results in (a) obtaining the general solution of Type VII_0 with the aid of the third Painlev\'{e} transcendental (b) obtaining the general solution of Type $VII_h$ with the aid of the sixth Painlev\'{e} transcendental (c) the recovery of all known solutions (six in total) without a prior assumption of any extra symmetry (d) The discovery of a new solution (the line element given in closed form) with a G_3 isometry group acting on T_3, i.e. on time-like hyper-surfaces, along with the emergence of the line element describing the flat vacuum Type VII_0 Bianchi Cosmology.Comment: latex2e source file, 27 pages, 2 tables, no fiure

Generalized Brans-Dicke theories

In Brans-Dicke theory a non-linear self interaction of a scalar field allows a possibility of realizing the late-time cosmic acceleration, while recovering the General Relativistic behavior at early cosmological epochs. We extend this to more general modified gravitational theories in which a de Sitter solution for dark energy exists without using a field potential. We derive a condition for the stability of the de Sitter point and study the background cosmological dynamics of such theories. We also restrict the allowed region of model parameters from the demand for the avoidance of ghosts and instabilities. A peculiar evolution of the field propagation speed allows us to distinguish those theories from the LCDM model.Comment: 14 pages, 4 figures, version to appear in JCA

Hubble flows and gravitational potentials in observable Universe

In this paper, we consider the Universe deep inside of the cell of uniformity. At these scales, the Universe is filled with inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies), which disturb the background Friedmann model. We propose mathematical models with conformally flat, hyperbolic and spherical spaces. For these models, we obtain the gravitational potential for an arbitrary number of randomly distributed inhomogeneities. In the cases of flat and hyperbolic spaces, the potential is finite at any point, including spatial infinity, and valid for an arbitrary number of gravitating sources. For both of these models, we investigate the motion of test masses (e.g., dwarf galaxies) in the vicinity of one of the inhomogeneities. We show that there is a distance from the inhomogeneity, at which the cosmological expansion prevails over the gravitational attraction and where test masses form the Hubble flow. For our group of galaxies, it happens at a few Mpc and the radius of the zero-acceleration sphere is of the order of 1 Mpc, which is very close to observations. Outside of this sphere, the dragging effect of the gravitational attraction goes very fast to zero.Comment: 21 pages, 5 figure

Gauge-ready formulation of the cosmological kinetic theory in generalized gravity theories

We present cosmological perturbations of kinetic components based on relativistic Boltzmann equations in the context of generalized gravity theories. Our general theory considers an arbitrary number of scalar fields generally coupled with the gravity, an arbitrary number of mutually interacting hydrodynamic fluids, and components described by the relativistic Boltzmann equations like massive/massless collisionless particles and the photon with the accompanying polarizations. We also include direct interactions among fluids and fields. The background FLRW model includes the general spatial curvature and the cosmological constant. We consider three different types of perturbations, and all the scalar-type perturbation equations are arranged in a gauge-ready form so that one can implement easily the convenient gauge conditions depending on the situation. In the numerical calculation of the Boltzmann equations we have implemented four different gauge conditions in a gauge-ready manner where two of them are new. By comparing solutions solved separately in different gauge conditions we can naturally check the numerical accuracy.Comment: 26 pages, 9 figures, revised thoroughly, to appear in Phys. Rev.