Chaplygin gas emerging from an effective description of inhomogeneous universe models (2009)
In the framework of spatially averaged inhomogeneous cosmologies in classical general relativity, effective Einstein equations govern the dynamics of averaged scalar variables in a scale-dependent...
On the Newtonian Limit of the Weyl Tensor (2009)
Ehlers, Juergen, Buchert, Thomas
In this note we wish to complement some recent work in the cosmological literature concerning the Weyl conformal curvature tensor and its parts. In particular, we shall give a clear-cut definition of...
Buchert, Thomas, Ellis, George F R, Van Elst, Henk
The thoughts expressed in this article are based on remarks made by J\"urgen Ehlers at the Albert-Einstein-Institut, Golm, Germany in July 2007. The main objective of this article is to demonstrate,...
Testing backreaction effects with observations (2008)
Larena, Julien, Alimi, Jean--Michel, Buchert, Thomas, Kunz, Martin, Corasaniti, Pier-Stefano
In order to quantitatively test the ability of averaged inhomogeneous cosmologies to correctly describe observations of the large scale properties of the Universe, we introduce a smoothed template...
On the curvature of the present-day Universe (2008)
Buchert, Thomas, Carfora, Mauro
We discuss the effect of curvature and matter inhomogeneities on the averaged scalar curvature of the present-day Universe. Motivated by studies of averaged inhomogeneous cosmologies, we contemplate...
Ricci flow deformation of cosmological initial data sets (2008)
Carfora, Mauro, Buchert, Thomas
Ricci flow deformation of cosmological initial data sets in general relativity is a technique for generating families of initial data sets which potentially would allow to interpolate between...
Taihei Yano, Hiroko Koyama, Thomas Buchert
We numerically investigate the long{time evolution of density perturbations after the rst appearance of caustics in an expanding cosmological model with one{dimensional `single{wave ' initial...
Dark Energy from structure: a status report (2007)
The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein's theory, restricting attention to...
Backreaction Issues in Relativistic Cosmology and the Dark Energy Debate (2006)
The effective evolution of an inhomogeneous universe model in Einstein's theory of gravitation may be described in terms of spatially averaged scalar variables. This evolution can be modeled by...
Reinterpreting quintessential dark energy through averaged inhomogeneous cosmologies (2006)
Larena, Julien, Buchert, Thomas, Alimi, Jean-Michel
Regionally averaged relativistic cosmologies have recently been considered as a possible explanation for the apparent late time acceleration of the Universe. This contribution reports on a mean field...
Buchert, Thomas, Larena, Julien, Alimi, Jean-Michel
Spatially averaged inhomogeneous cosmologies in classical general relativity can be written in the form of effective Friedmann equations with sources that include backreaction terms. In this paper we...
The non-perturbative regime of cosmic structure formation (2006)
This paper focusses on the barely understood gap between the weakly nonlinear regime of structure formation and the onset of the virialized regime. While the former is accessed through perturbative...
In the framework of spatially averaged inhomogeneous cosmologies in classical General Relativity, effective Einstein equations govern the regional and the global dynamics of averaged scalar variables...
An exact Lagrangian integral for the Newtonian gravitational field strength (2005)
An exact expression for the gravitational field strength in a self-gravitating dust continuum is derived within the Lagrangian picture of continuum mechanics. From the Euler-Newton system a transport...
A system of effective Einstein equations for spatially averaged scalar variables of inhomogeneous cosmological models can be solved by providing a `cosmic equation of state'. Recent efforts to...
Adhesive Gravitational Clustering (2005)
Buchert, Thomas, Dominguez, Alvaro
The notion of `adhesion' has been advanced for the phenomenon of stabilization of large-scale structure emerging from gravitational instability of a cold medium. Recently, the physical origin of...
Information Entropy in Cosmology (2004)
Hosoya, Akio, Buchert, Thomas, Morita, Masaaki
The effective evolution of an inhomogeneous cosmological model may be described in terms of spatially averaged variables. We point out that in this context, quite naturally, a measure arises which is...
The Cosmic Quartet - Cosmological Parameters of a Smoothed Inhomogeneous Spacetime (2003)
Buchert, Thomas, Carfora, Mauro
We discuss the relation between `bare' cosmological parameters as the true spatial average characteristics that determine the cosmological model, and the parameters interpreted by observers with a...
Universality in the distribution of caustics in the expanding Universe (2003)
Yano, Taihei, Koyama, Hiroko, Buchert, Thomas, Gouda, Naoteru
We numerically investigate the long--time evolution of density perturbations after the first appearance of caustics in an expanding cosmological model with one--dimensional `single--wave' initial...
Minkowski Functionals of SDSS galaxies I : Analysis of Excursion Sets (2003)
Hikage, Chiaki, Schmalzing, Jens, Buchert, Thomas, Suto, Yasushi, Kayo, Issha, Taruya, Atsushi, ...
We present a first morphometric investigation of a preliminary sample from the SDSS of 154287 galaxies with apparent magnitude 14.5
Minkowski Functionals of SDSS galaxies I: Analysis of Excursion Sets (2003)
Chiaki Hikage, Jens Schmalzing, Thomas Buchert, Yasushi Suto, Issha Kayo, Atsushi Taruya, ...
We present a rst morphometric investigation of a preliminary sample from the SDSS of 154287 galaxies with apparent magnitude 14:5 < m r < 17:5 and redshift 0:001 < z < 0:4. We measure the...
Cosmological parameters are dressed (2002)
Buchert, Thomas, Carfora, Mauro
In the context of the averaging problem in relativistic cosmology, we provide a key to the interpretation of cosmological parameters by taking into account the actual inhomogeneous geometry of the...
Regional averaging and scaling in relativistic cosmology (2002)
Buchert, Thomas, Carfora, Mauro
Averaged inhomogeneous cosmologies lie at the forefront of interest, since cosmological parameters like the rate of expansion or the mass density are to be considered as volume-averaged quantities...
The Cosmic Quartet - Cosmological Parameters of a Smoothed Inhomogeneous Spacetime (2002)
We discuss the relation between `bare' cosmological parameters as the true spatial average characteristics that determine the cosmological model, and the parameters interpreted by observers with...
Regional Averaging and Scaling in Relativistic Cosmology (2002)
Thomas Buchert, Mauro Carfora, Theoretische Physik
Averaged inhomogeneous cosmologies lie at the forefront of interest, since cosmological parameters like the rate of expansion or the mass density are to be considered as volume{averaged quantities...
For general relativistic spacetimes filled with an irrotational perfect fluid a generalized form of Friedmann's equations governing the expansion factor of spatially averaged portions of...
Matter seen at many scales and the geometry of averaging in relativistic cosmology (2001)
Buchert, Thomas, Carfora, Mauro
We investigate the scale-dependence of Eulerian volume averages of scalar functions on Riemannian three-manifolds. We propose a complementary view of a Lagrangian scaling of variables as opposed to...
On the abundance of collapsed objects (2000)
Kerscher, Martin, Buchert, Thomas, Futamase, Toshifumi
The redshift dependence of the abundance of collapsed objects places strong constraints on cosmological models of structure formation. We apply a recently proposed model describing the anisotropic...
On average properties of inhomogeneous cosmologies (2000)
The present talk summarizes the recently progressed state of a systematic re-evaluation of cosmological models that respect the presence of inhomogeneities. Emphasis is given to identifying the basic...
Backreaction of inhomogeneities on the expansion: the evolution of cosmological parameters (1999)
Buchert, Thomas, Kerscher, Martin, Sicka, Christian
Averaging and evolving inhomogeneities are non-commuting operations. This implies the existence of deviations of an averaged model from the standard Friedmann-Lemaitre cosmologies. We quantify these...
Backreaction in Cosmological Models (1999)
Sicka, Christian, Buchert, Thomas, Kerscher, Martin
Most cosmological models studied today are based on the assumption of homogeneity and isotropy. Observationally one can find evidence that supports these assumptions on very large scales, the...
On average properties of inhomogeneous fluids in general relativity I: dust cosmologies (1999)
For general relativistic spacetimes filled with irrotational `dust' a generalized form of Friedmann's equations for an `effective' expansion factor $a_D (t)$ of inhomogeneous cosmologies is derived....
Disentangling the Cosmic Web I: Morphology of Isodensity Contours (1999)
Schmalzing, Jens, Buchert, Thomas, Melott, Adrian L., Sahni, Varun, Sathyaprakash, B. S., Shandarin, Sergei F.
We apply Minkowski functionals and various derived measures to decipher the morphological properties of large-scale structure seen in simulations of gravitational evolution. Minkowski functionals of...
Stabilization of Large Scale Structure by Adhesive Gravitational Clustering (1999)
The interplay between gravitational and dispersive forces in a multi-streamed medium leads to an effect which is exposed in the present note as the genuine driving force of stabilization of...
Disentangling the Cosmic Web I: Morphology of Isodensity Contours (1999)
Jens Schmalzing Thomas, Thomas Buchert, Varun Sahni, B. S. Sathyaprakash, Sergei F. Sh
We apply Minkowski functionals and various derived measures to decipher the morphological properties of large--scale structure seen in simulations of gravitational evolution. Minkowski functionals of...
On Statistics and Dynamics of Cosmic Structure (1999)
Jens Schmalzing, Jens Schmalzing, Thomas Buchert, Zweitgutachter Prof, Gerhard Börner
Among the sciences, cosmology finds itself in the peculiar situation that it studies a unique object, namely the entire Universe. Nevertheless, it is possible...
A global descriptor of spatial pattern interaction in the galaxy distribution (1999)
Martin Kerscher, María Jesús Pons–bordería, Jens Schmalzing, Thomas Buchert, Vicentj. Martínez, Riccardo Valdarnini
We present the function J as a morphological descriptor for point patterns formed by the distribution of galaxies in the Universe. This function was recently introduced in the field of spatial...
Lagrangian theory of structure formation in pressure-supported cosmological fluids (1998)
Adler, Susanne, Buchert, Thomas
The Lagrangian theory of structure formation in cosmological fluids, restricted to the matter model ``dust'', provides successful models of large-scale structure in the Universe in the laminar...
Fritsch, Christoph, Buchert, Thomas
We discuss implications of the fundamental plane parameters of clusters of galaxies derived from combined optical and X-ray data of a sample of 78 nearby clusters. In particular, we investigate the...
A global descriptor of spatial pattern interaction in the galaxy distribution (1997)
Kerscher, Martin, Pons-Borderia, Maria Jesus, Schmalzing, Jens, Trasarti-Battistoni, Roberto, Buchert, Thomas, Martinez, Vicent J., ...
We present the function J as a morphological descriptor for point patterns formed by the distribution of galaxies in the Universe. This function was recently introduced in the field of spatial...
A fresh look at the adhesion approximation (1997)
I report on a systematic derivation of the phenomenological ``adhesion approximation'' from gravitational instability together with a brief evaluation of the related status of analytical modeling of...
Characterizing cluster morphology using vector-valued Minkowski functionals (1997)
Beisbart, Claus, Buchert, Thomas
The morphology of galaxy clusters is quantified using Minkowski functionals, especially the vector-valued ones, which contain directional information and are related to curvature centroids. The...
Extending the scope of models for large-scale structure formation in the Universe (1997)
Buchert, Thomas, Dominguez, Alvaro, Perez-Mercader, Juan
We propose a phenomenological generalization of the models of large-scale structure formation in the Universe by gravitational instability in two ways: we include pressure forces to model...
Averaging Inhomogeneous Cosmologies -- a Dialogue (1997)
The averaging problem for inhomogeneous cosmologies is discussed in the form of a disputation between two cosmologists, one of them (RED) advocating the standard model, the other (GREEN) advancing...
The Significance of the Fluctuations in the IRAS 1.2 Jy Galaxy Catalogue (1997)
Kerscher, Martin, Schmalzing, Jens, Buchert, Thomas, Wagner, Herbert
In an analysis of the IRAS 1.2 Jy redshift catalogue, with emphasis on the separate examination of northern and southern parts (in galactic coordinates), we found that the clustering of galaxies...
Fluctuations in the IRAS 1.2 Jy Catalogue (1997)
Kerscher, Martin, Schmalzing, Jens, Buchert, Thomas, Wagner, Herbert
An analysis of the IRAS 1.2 Jy redshift catalogue with emphasis on the separate examination of northern and southern parts (in galactic coordinates) is performed using a complete set of morphological...
Buchert, Thomas, Dominguez, Alvaro
The generally held view that a model of large-scale structure, formed by collisionless matter in the Universe, can be based on the matter model ``dust'' fails in the presence of multi-stream flow,...
Beyond genus statistics: a unifying approach to the morphology of cosmic structure (1997)
Schmalzing, Jens, Buchert, Thomas
The genus statistics of isodensity contours has become a well-established tool in cosmology. In this Letter we place the genus in the wider framework of a complete family of morphological...
Newtonian Cosmology in Lagrangian Formulation: Foundations and Perturbation Theory (1997)
Ehlers, Jürgen, Buchert, Thomas
The ldquoNewtonianrdquo theory of spatially unbounded, self-gravitating, pressureless continua in Lagrangian form is reconsidered. Following a review of the pertinent kinematics, we present...
What do we know about global properties of the universe (1997)
Börner, Gerhard, Buchert, Thomas, Ehlers, Jürgen, Ellis, George F. R., Hogan, C. J., Kirshner, R. P., ...
Newtonian Cosmology in Lagrangian Formulation: Foundations and Perturbation Theory (1996)
Ehlers, Juergen, Buchert, Thomas
The ``Newtonian'' theory of spatially unbounded, self--gravitating, pressureless continua in Lagrangian form is reconsidered. Following a review of the pertinent kinematics, we present alternative...
The performance of Lagrangian perturbation schemes at high resolution (1995)
Buchert, Thomas, Karakatsanis, Georgios, Klaffl, Robert, Schiller, Peter
We present high--spatial resolution studies of the density field as predicted by Lagrangian perturbation approximations up to the third order. The first--order approximation is equivalent to the...
Averaging inhomogeneous Newtonian cosmologies (1995)
Buchert, Thomas, Ehlers, Juergen
Idealizing matter as a pressureless fluid and representing its motion by a peculiar--velocity field superimposed on a homogeneous and isotropic Hubble expansion, we apply (Lagrangian) spatial...
Applications of Minkowski Functionals to the Statistical Analysis of Dark Matter Models (1995)
Platzoeder, Michael, Buchert, Thomas
A new method for the statistical analysis of 3D point processes, based on the family of Minkowski functionals, is explained and applied to modelled galaxy distributions generated by a toy-model and...
Optimizing Higher-Order Lagrangian Perturbation Theory for Standard CDM and BSI models (1995)
Weiss, Arno G., Gottloeber, Stefan, Buchert, Thomas
We investigate the performance of Lagrangian perturbation theory up to the second order for two scenarios of cosmological large-scale structure formation, SCDM (standard cold dark matter) and BSI...
Cosmic density and velocity fields in Lagrangian perturbation theory (1995)
Susperregi, Mikel, Buchert, Thomas
A first- and second-order relation between cosmic density and peculiar-velocity fields is presented. The calculation is purely Lagrangian and it is derived using the second-order solutions of the...
The Lagrangian perturbation theory on Friedman-Lemaitre cosmologies investigated and solved up to the second order in earlier papers (Buchert 1992, Buchert \& Ehlers 1993) is evaluated up to the...
Die PANCAKE-Theorie der Bildung supergalaktischer Strukturen : analyt. Grundlagen. (1988)
München, Techn. Univ., Diss., 1988.