Cosmological Corrections Research Articles

Black hole evaporation in an expanding universe

We calculate the quantum radiation power of black holes which are asymptotic to the Einstein–de Sitter universe at spatial and null infinities. We consider two limiting mass accretion scenarios, no accretion and significant accretion. We find that the radiation power strongly depends on not only the asymptotic condition but also the mass accretion scenario. For the no accretion case, we consider the Einstein–Straus solution, where a black hole of constant mass resides in the dust Friedmann universe. We find negative cosmological correction besides the expected redshift factor. This is given in terms of the cubic root of ratio in size of the black hole to the cosmological horizon, so that it is currently of order 10−5(M/106M⊙)1/3(t/14Gyr)−1/3 but could have been significant at the formation epoch of primordial black holes. Due to the cosmological effects, this black hole has not settled down to an equilibrium state. This cosmological correction may be interpreted in an analogy with the radiation from a moving mirror in a flat spacetime. For the significant accretion case, we consider the Sultana–Dyer solution, where a black hole tends to increase its mass in proportion to the cosmological scale factor. In this model, we find that the radiation power is apparently the same as the Hawking radiation from the Schwarzschild black hole of which mass is that of the growing mass at each moment. Hence, the energy loss rate decreases and tends to vanish as time proceeds. Consequently, the energy loss due to evaporation is insignificant compared to huge mass accretion onto the black hole. Based on this model, we propose a definition of quasi-equilibrium temperature for general conformal stationary black holes.

Curvature corrections in DGP brane cosmology

We consider a DGP-inspired brane scenario where the action on the brane is augmented bya function of the Ricci scalar, . The cosmological implications that such a scenario entails are examined forRn and shown to be consistent with a universe expanding with power-law acceleration. Itis shown that two classes of solutions exist for the usual FRW metric andsmall Hubble radii. When the Hubble radius becomes larger, we either have atransition to a fully 5D regime or to a self-inflationary solution which producesa late accelerated expansion such that the radius becomes a function ofn.

The effect of α′ corrections in string gas cosmology

In the Brandenberger–Vafa scenario of string gas cosmology, the Universe starts as a small torus of string length dimension filled with a hot gas of strings. In such extreme conditions, in addition to the departure from Einstein gravity which is due to the dilaton, one expects higher curvature corrections to be relevant. Motivated by this fact, we study the effect of the leading α′3 corrections in type IIB string theory for this scenario. Within the assumptions of: weak coupling, adiabatic evolution and thermodynamical equilibrium, we perturbatively solved the corresponding equations of motion in two different cases: (i) the isotropic case which is governed by a single scale factor and (ii) the anisotropic case given by two different scale factors. In the first case, we consider two regimes: (ia) the Hagedorn regime where the string gas equation of state is that of pressureless dust and (ib) the radiation regime. In the second case, (ii), we only considered a radiation-like equation of state. We found that the inclusion of α′ corrections affects the scale factor(s) in the opposite way in the Hagedorn and in the radiation regimes, acting as a driving force for the first one and a damping force for the second one. This effect is small for reasonable initial conditions and it is only observed at early times. Moreover it is bigger in the Hagedorn regime than in the radiation regime. We also analysed the fixed points of the system. We found that there exists a stable dS fixed point, which does not exist when the corrections are neglected.

Galaxy properties and photometric redshifts

We present GALEV evolutionary synthesis models for Simple Stellar Populations (SSPs = single burst, single metallicity) like star clusters or galaxy pixels and for galaxies of various types on the basis of their respective typical star formation histories, ranging from exponentially declining on a timescale of 1Gyr for the classical elliptical model through constant for Sd galaxies, and also allowing for starbursts of various strengths occurring at various evolutionary stages. Models yield the time evolution of the stellar population in terms of color-magnitude diagrams CMDs () and consistently accounting for evolutionary and cosmological corrections as well as for the attenuation of light from distant galaxies by intervening HI.

Decay properties of the X-ray afterglows of gamma-ray bursts

We present a set of seventeen Gamma-Ray Bursts (GRBs) with known redshifts and X-ray afterglow emission. We apply cosmological corrections in order to compare their fluxes normalized at a redshift of 1. Two classes of GRB can be defined using their X-ray afterglow light curves. We show that the brightest afterglows seem to decay faster than the dimer ones. We also point out evidences for a possible flux limit of the X-ray afterglow depending on the time elapsed since the burst. We try to interpret these observations in the framework of the canonical fireball model of GRB afterglow emission.

FRIEDMANN–ROBERTSON–WALKER BRANE COSMOLOGICAL EQUATIONS FROM THE FIVE-DIMENSIONAL BULk (A)dS BLACK HOLE

In the first part of this work we review the equations of motion for the brane presented in Friedmann–Robertson–Walker (FRW) form, when the bulk is five-dimensional (A)dS Black Hole. The spacelike (timelike) FRW brane equations are considered from the point of view of their representation in the form similar to two-dimensional CFT entropy, the so-called Cardy–Verlinde (CV) formula. The following five-dimensional gravities are reviewed: Einstein, Einstein–Maxwell and Einstein with brane quantum corrections. The second part of the work is devoted to the study of FRW brane equations and their representation in CV form, brane induced matter and brane cosmology in Einstein–Gauss–Bonnet (GB) gravity. In particular, we focus on the inflationary brane cosmology. The energy conditions for brane matter are also analyzed. We show that for some values of GB coupling constant (bulk is AdS BH) the brane matter is not CFT. Its energy density and pressure are not always positive. The appearance of logarithmic corrections in brane cosmology is discussed.

The X-ray surface brightness profiles of hot galaxy clusters up to $\vec z$ ~ 0.8: Evidence for self-similarity and constraints on $\Omega_\mathsf{0}$

We study the surface brightness profiles of a sample of 25 distant hot clusters, observed with ROSAT, with published temperatures from ASCA. For both open and flat cosmological models, the derived emission measure profiles are scaled according to the self-similar model of cluster formation. We use the standard scaling relations of cluster properties with redshift and temperature, with the empirical slope of the relation derived by Neumann & Arnaud ([CITE]). Using a test, we perform a quantitative comparison of the scaled emission measure profiles of distant clusters with a local reference profile derived from the sample of 15 hot nearby clusters compiled by Neumann & Arnaud (1999), which were found to obey self-similarity. This comparison allows us to both check the validity of the self-similar model across the redshift range , and to constrain the cosmological parameters. For a low-density flat universe, the scaled distant cluster data were found to be consistent, both in shape and normalisation, with the local reference profile. It indicates that hot clusters constitute a homologous family up to high redshifts, and gives support to the standard picture of structure formation for the dark matter component. Because of the intrinsic regularity in the hot cluster population, the scaled profiles can be used as distance indicators, the correct cosmology being the one for which the various profiles at different redshifts coincide. The intrinsic limitations of the method, in particular possible systematic errors and biases related to the model uncertainties, are discussed. Using the standard evolution model, the present data allow us to put a tight constraint on for a flat Universe: at 90% confidence level (statistical errors only). The critical model () was excluded at the 98% confidence level. Consistently, the observed evolution of the normalisation of the relation was found to comply with the self-similar model for , . The constraint derived on is in remarkable agreement with the constraint obtained from luminosity distances to SNI or from combined analysis of the power spectrum of the 2dF galaxy redshift Survey and the Cosmic Microwave Background anisotropies.

Single-brane cosmological solutions with a stable compact extra dimension

We consider 5-dimensional cosmological solutions of a single brane. The correct cosmology on the brane, i.e., governed by the standard 4-dimensional Friedmann equation, and stable compactification of the extra dimension is guaranteed by the existence of a non-vanishing \hat{T}^5_5 which is proportional to the 4-dimensional trace of the energy-momentum tensor. We show that this component of the energy-momentum tensor arises from the backreaction of the dilaton coupling to the brane. The same positive features are exhibited in solutions found in the presence of non-vanishing cosmological constants both on the brane (\Lambda_{br}) and in the bulk (\Lambda_B). Moreover, the restoration of the Friedmann equation, with the correct sign, takes place for both signs of $\Lambda_B$ so long as the sign of $\Lambda_{br}$ is opposite $\Lambda_B$ in order to cancel the energy densities of the two cosmological constants. We further extend our single-brane thin-wall solution to allow a brane with finite thickness.

Classical corrections in string cosmology

An important element in a model of non-singular string cosmology is a phase in which classical corrections saturate the growth of curvature in a deSitter-like phase with a linearly growing dilaton (an `algebraic fixed point'). As the form of the classical corrections is not well known, here we look for evidence, based on a suggested symmetry of the action, scale factor duality and on conformal field theory considerations, that they can produce this saturation. It has previously been observed that imposing scale factor duality on the $O(\alpha')$ corrections is not compatible with fixed point behavior. Here we present arguments that these problems persist to all orders in $\alpha'$. We also present evidence for the form of a solution to the equations of motion using conformal perturbation theory, examine its implications for the form of the effective action and find novel fixed point structure.

Evolutionary and Cosmological Corrections for High Redshift Galaxies

We calculate the evolution of high redshift galaxies by spectral type with our unified chemically consistent spectrophotometric evolution code. This model takes into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary tracks, color calibrations and spectra (Möller et al. 1997).We analyse how the consideration of a realistic metallicity distribution affects the evolutionary and cosmological corrections in various bands as a function of redshift. For various spectral types of galaxies and various cosmological parameters we present the color and magnitude evolution as a function of redshift and compare them with observations.

The Influence of the Cosmological Expansion on Local Systems

Following renewed interest, the problem of whether the cosmological expansion affects the dynamics of local systems is reconsidered. The cosmological correction to the equations of motion in the locally inertial Fermi normal frame (the relevant frame for astronomical observations) is computed. The evolution equations for the cosmological perturbation of the two-body problem are solved in this frame. The effect on the orbit is insignificant, as are the effects on the galactic and galactic-cluster scales.

Effective potential approach to finite temperature quantum cosmology

We consider one-loop corrections in finite temperature quantum cosmology in the statis approximation. An exact expression for the effective potential of the Coleman-Weinberg type is given for the scalar field in a closed cosmological model. The role of non-zero temperature and non-zero curvature quantum corrections due to the non-trivial S 1×S 3 topology is discussed. Quantum topological effects of mass generation of the self-interacting scalar field as well as zero-point fluctuation energy are examined.

Inner ring structures in galaxies as distance indicators. IV - Distances to several groups, clusters, the Hercules supercluster, and the value of the Hubble constant

view Abstract Citations (40) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Inner ring structures in galaxies as distance indicators. IV. Distances to several groups, clusters, the Hercules supercluster, and the value of the Hubble constant. Buta, R. ; de Vaucouleurs, G. Abstract The extragalactic distance scale derived in previous papers of this series from the diameters of inner ring structures (r) in galaxies is applied to the determination of the distances of six groups and clusters, and one supercluster, in the distance range to 10 ≤ Δ ≤ 112 Mpc. The clusters are well distributed on the sky and are used to derive a value of the Hubble constant free of the perturbing effects of the Local Supercluster. Several definitions of the Hubble ratio, for bound and unbound systems, and several frames of reference are introduced and used. Radial velocities Vc corrected for solar motion in a frame of reference defined by the nearby galaxies (2 ≤ Δ ≤ 32 Mpc) are shown to yield a Hubble ratio which is substantially independent of direction. An analysis of four bound groups and one unbound grouping in the distance interval 10 ≤ Δ ≤ 16 Mpc yields a mean Hubble ratio Hc = 92 ±+ 4 (internal m.e.) km s-1 Mpc-1. A similar analysis of two more distant bound systems, the IC 4329 Group at Δ = 45 Mpc and the Hercules Supercluster at Δ = 112 Mpc, yields Hc = 96 ± 5 or 93 ± 5 when plausible cosmological corrections are considered. The constancy of the Hubble ratio over the distance range 10 ≤ Δ ≤ 112 Mpc gives no support to nonlinear concepts of the redshift-distance relation and demonstrates the absence of Malmquist bias in the μ0(r) scale. The value of the Hubble constant derived from the rings over this range is H0 = 93 1 ± 4 (internal m.e.) km s-1 Mpc-1 and ±10 (external m.e.) when the zero point error of our tertiary indicators is included. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/160754 Bibcode: 1983ApJ...266....1B Keywords: Astrometry; Cosmology; Galactic Clusters; Galactic Structure; Distance; Hubble Diagram; Radial Velocity; Red Shift; Ring Structures; Spiral Galaxies; Virgo Galactic Cluster; Astrophysics full text sources ADS | data products NED (52) SIMBAD (51) Related Materials (4) Part 1: 1980ApJS...44..451D Part 2: 1982ApJS...48..219B Part 3: 1983ApJS...51..149B Part 5: 1983ApJ...272..380B

Dynamical symmetry breaking due to radiative corrections in cosmology

Dynamical symmetry breaking in massless $\ensuremath{\lambda}{\ensuremath{\varphi}}^{4}$ theory in curved spacetime with non-conformal coupling to the curvature is investigated. It is shown that in general the one-loop self-energy for such a field will involve a term of the form $R\mathrm{ln}|R{\ensuremath{\mu}}^{\ensuremath{-}2}|$, where $R$ is the scalar curvature, and $\ensuremath{\mu}$ is a mass. This term can give rise to symmetry breaking. Two models, the Einstein universe and a spatially flat Robertson-Walker universe with a power-law expansion, are considered where this term is the sole contribution to the one-loop self-energy. In both cases a phase transition will occur at a critical value of the curvature. The form of the two-loop corrections to the self-energy and the limits of validity of the one-loop approximation are discussed.