2374089
Numerical study of the cosmological velocity field as a function of density
We report on a new study of the velocity distribution in N-body simulations. We investigate the center-of-mass and internal kinetic energies of coarsening cells as a function of time, cell size and cell mass. By using self-similar cosmological models, we are able to derive theoretical predictions for comparison and to assess the influence of finite-size and resolution effects. The most interesting result is the discovery of a polytropic-like relationship between the average velocity dispersion (internal kinetic energy) and the mass density in an intermediate range of densities, κint ∝ � 2−η . The exponent η measures the deviations from the virial prediction, ηvirial = 0. For self-similar models, η depends only on the spectral index of the initial power spectrum. We also study CDM models and confirm a previous result that the same polytropic-like dependence exists, with a time and coarsening length dependent η. The dependence κint(� ) is an important input for a recently proposed theoretical model of cosmological structure formation which improves over the standard dust model (pressureless fluid) by regularizing the density singularities.
14575890
Morphology of the large-scale structure
The Minkowski functionals are a mathematical tool to quantify morphological features of patterns. Some applications to the matter distribution in galaxy catalogues and N-body simulations are reviewed, with an emphasis on the effects of cosmic variance. The conclusions are that (i) the observed large-scale morphology is sensitive to cosmic variance on scales much larger than the nonlinear length (approx. 8 Mpc/h), and (ii) the large-scale morphology predicted by simulations is thus affected by finite-size effects, but nonetheless a Lambda-CDM model is favored.
13112109
Velocity dispersion in N-body simulations of CDM models
This work reports on a study of the spatially coarse-grained velocity dispersion in cosmological N-body simulations (OCDM and ΛCDM models) as a function of time (redshifts z = 0–4) and of the coarsening length (0.6–20 h−1 Mpc). The main result is the discovery of a polytropic relationship ℐ1 ∝ ϱ2–η between the velocity-dispersion kinetic energy density of the coarsening cells, ℐ1, and their mass density, ϱ. The exponent η, dependent on time and coarsening scale, is a compact measure of the deviations from the naive virial prediction ηvirial = 0. This relationship supports the “polytropic assumption” which has been employed in theoretical models for the growth of cosmological structure by gravitational instability. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
10408360
Scaling laws in the cosmic structure and renormalization group
There is an evidence of a scale-invariant matter distribution up to scales over 10 Mpc. We review scaling (fractal or multifractal) models of large-scale structure and their observational evidence. We conclude that the dynamics of cosmological structure formation seems to be driven to a multifractal attractor. This supports previous studies, which we review, of structure formation by means of the renormalization group within a hydrodynamic formulation.
42350703
Large quantum gravity effects and nonlocal variables
We reconsider here the model where large quantum gravity effects were first found, but now in its null surface formulation (NSF). We find that although the set of coherent states for Z, the basic variable of NSF, is as restricted as is the one for the metric, while some type of small deviations from these states may cause huge fluctuations on the metric, the corresponding fluctuations on Z remain small.
119520371
A Gravitational memory effect in 'boosted' black hole perturbation theory
Black hole perturbation theory, or more generally, perturbation theory on a Schwarzschild bockground, has been applied in several contexts, but usually under the simplifying assumption that the ADM momentum vanishes, namely, that the evolution is carried out and observed in the ``center of momentum frame''. In this paper we consider some consequences of the inclusion of a non vanishing ADM momentum in the initial data. We first provide a justification for the validity of the transformation of the initial data to the ``center of momentum frame'', and then analyze the effect of this transformation on the gravitational wave amplitude. The most significant result is the possibility of a type of gravitational memory effect that appears to have no simple relation with the well known Christodoulou effect.