Brane cosmology from observational surveys and its comparison with standard FRW cosmology

Several simple dark energy models on the brane are investigated. They are compared with corresponding models in the frame of 4d Friedmann-Robertson-Walker cosmology. For constraining the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Also, explicit formulas of the so-called state-finder parameters in teleparallel theories are found that could be useful to test these models and compare Loop Quantum Cosmology and Brane Cosmology. The conclusion is reached that a joint analysis as the one developed here allows to estimate, in a very clear way, possible deviation of our cosmology from the standard Friedmann-Robertson-Walker one.     

Steady-state versus viscous cosmology

Hoyle's steady-state cosmology and relativistic Robertson-Walker world models with a constant bulk viscosity are briefly reviewed and compared. It is shown that, although they are identifical from a purely formal point of view, the interpretation of Hoyle's model in terms of viscous dissipation would be physically unrealistic.     

Bounce solutions in viscous fluid cosmology

We investigate the bounce cosmology induced by inhomogeneous viscous fluids in FRW space-time (non necessarily flat), taking into account the early-time acceleration after the bounce. Different forms for the scale factor and several examples of fluids will be considered. We also analyze the relation between bounce and finite-time singularities and between the corresponding fluids realizing this scenarios. In the last part of the work, the study is extended to the framework of f(R)-modified gravity, where the modification of gravity may also be considered as an effective (viscous) fluid producing the bounce.     

FRW bulk viscous cosmology with modified cosmic Chaplygin gas

In this paper we study FRW bulk viscous cosmology in presence of modified cosmic Chaplygin gas. We obtain generalized Friedmann equations due to bulk viscosity and modified cosmic Chaplygin gas. Then, we calculate time-dependent energy density and discuss Hubble expansion parameter.     

FRW bulk viscous cosmology with modified Chaplygin gas in flat space

In this paper we study FRW bulk viscous cosmology in presence of modified Chaplygin gas. We write modified Friedmann equations due to bulk viscosity and Chaplygin gas and obtain time-dependent energy density for the special case of flat space.     

String cosmology with magnetized bulk viscous fluid in Bianchi I universe

The objective of the present paper is to study an anisotropic Bianchi-I cosmological model filled with bulk viscous fluid and magnetic field in string cosmology. The magnetic field is due to an electric current produced along the x-axis. The expansion in the model is considered to be proportional to one of the components of the shear tensor. We obtain two different quadrature forms of volume scale factor by considering two different relations between bulk viscosity and expansion scalar. We discuss the behavior of the classical potential with respect to the volume scale factor in the presence or absence of magnetic field and bulk viscosity in each case. We observe the role of bulk viscosity on the classical potential and also on the choices of bulk viscous pressure. By introduction of magnetic field or bulk viscosity or both into the model it results in changes in the potential as well as in volume scale factors. The physical and geometrical aspects of the solutions are discussed in detail.     

Integrated Sachs–Wolfe effect in the era of precision cosmology

Recent detection of the Integrated Sachs–Wolfe (ISW) effect through correlation of the cosmic microwave background temperature anisotropy with traces of large scale structure provided independent evidence for the expansion of the universe being dominated by something other than matter. In these conference proceedings I discuss the extent to which future ISW measurements can help in precision tests of the physics responsible for the observed cosmic acceleration.     

Bianchi II,VIII, and IX viscous fluid cosmology

In this paper we study the exact solutions for a viscous fluid distribution in Bianchi II, VIII, and IX models. The metric is simplified by assuming a relationship between the coefficients of the metric tensor. Solutions are obtained in two special cases: in one an additional assumption is made where the matter density and the expansion scalar have a definite relation and in the other a barotropic equation of state of the formp= is assumed. While the Bianchi II solutions are already found in the literature the other two classes of solutions are apparently new.     

Introduction to plasma astrophysics and cosmology

The year 1996 marks the Centennial Celebration of the founding of Plasma Astrophysics and Cosmology; its origins may be traced to the seminal research first published by Kristian Birkeland in 1896. This special workshop issue reports on advances in issues of importance to the plasma universe; topics as timely as when first raised a century ago.     

Warm anisotropic inflation with bulk viscous pressure in intermediate era

The aim of this paper is to study the warm inflation during intermediate era in the framework of locally rotationally symmetric Bianchi type I universe model. We assume that the universe is composed of inflaton and imperfect fluid having radiation and bulk viscous pressure. To this end, dynamical equations (first model field equation and energy conservation equations) under slow-roll approximation and in high dissipative regime are constructed. A necessary condition is developed for the realization of this anisotropic model. We assume both dissipation and bulk viscous coefficients variable as well as constant. We evaluate entropy density, scalar (tensor) power spectra, their corresponding spectral indices, tensor–scalar ratio and running of spectral index in terms of inflaton. These cosmological parameters are constrained using recent Planck and WMAP7 probe.     

Varying Constants in Brane World Scenarios

Higher-dimensional theories imply that some constants, such as the gravitational constant and the strength of the gauge-couplings, are not fundamental constants. Instead they are related to the sizes of the extra-dimensional space, which are moduli fields in the four-dimensional effective theory. We study the cosmological evolution of the moduli fields appearing in brane world scenarios and discuss the implications for varying constants. This revised version was published online in July 2006 with corrections to the Cover Date.     

The X‐ray‐infrared/submillimetre connection and the legacy era of cosmology

We review some recent results on the identification and characterisation of Active Galactic Nuclei (AGN) obtained by cross correlating X‐ray surveys with infrared and submillimetre surveys. We also look toward the scientific gains that could be achieved from an XMM‐Newton survey of the medium‐deep legacy fields that are being observed at ≈ 1–850 μm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Jeans-mass in cosmology

The matter of the Universe after recombination is considered as an expanding gas. the Jeans-mass obtained for this gas may essentially be larger than it is usually expected. This means that the discrepancy between the theoretical Jeans-mass and the observed masses of the galaxies may be mitigated.     

Turbulence in cosmology

Principles of the theory of turbulence in relativistic cosmology are developed. By averaging Einstein's equations over stochastic fields a self-consistent system of equations is obtained which describes statistically: (1) the influence of the turbulence on the ‘basic state of the Universe (the background) on which the turbulence develops; (2) the behaviour of the turbulence on the background ‘distorted’ by it. By means of a qualitative study of exact equations in the region of a strong turbulence at an early stage of cosmological expansion conditions of the absence of singularity are found and the possibility of stationary solutions in the homogeneous, isotropic, on the average, Universe (the cosmological constantA=0) is shown. The rate of cosmological expansion increases if the energy density of the turbulence is positive, and decreases if it is negative. The latter alternative takes place if the absolute value of the energy density of excitations, which will change into potential motions in the future, exceeds the energy density of the remaining part of the turbulence.     

Turbulence in cosmology

On the basis of the theory set out in Papers I and II (Marochniket al., 1975a, b), the kinetic equations for the spectra of classical and quantum short-wave turbulences have been obtained, taking account of the influence of the latter on the process of cosmological expansion of a homogeneous and, on average, isotropic Universe. The equilibrium and stationary spectra of the turbulence do not change the form of the cosmological solution found in II. The latter change if the spectra are non-stationary, or if the dissipation is taken into account. It is possible that a situation exists in which the primordial short-wave turbulence, having had a significant influence on the early metric, would not be observable at the present time. Quantum turbulence has been studied. Its influence on the metric may be significant only near the Planckian timet _g.     

Turbulence in cosmology

The influence of short-wave turbulence on the expansion of a homogeneous and, on average, isotropic Universe was studied in Papers I–III. In the present paper we study the influence on the manner of expansion, for a complete spectrum of wavelengths, of scalar, tensor and vector perturbations. Ast»0, all waves become long (greater than the horizon); therefore, a knowledge of their influence on the averaged metric is required. It is shown that the long-wave modes of scalar and tensor perturbations which remain finite ast»0 deflect the metric for a homogeneous and, on average, isotropic Universe from the Friedmannian, giving it a form coinciding with the average quasi-isotropic solution of Lifshitz and Khalatnikov (1963). Ast»0 their contribution to the solution tends to zero. What remains to be determined is the contribution of those modes of scalar, tensor and vector perturbations which diverge ast»0. Att=0 the proposed solution for such modes becomes inapplicable. The behaviour of the metric of a homogeneous and, on average, isotropic Universe under the influence of all waves and all modes of perturbation is shown in Figure 1–3.     

Stiff-matter solitons in cosmology

We study exact solutions of the Einstein field equations of the cylindrical-symmetric Einstein-Rosen type with stiff matter (p=) as a source with development and collisions of solitons associated with the metric and the fluid.Supported by a CONICET fellowship.