Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 0709.2558

Modified Averaging Processes in Cosmology and the Structured FRW model

Shahram Khosravi·Ehsan Kourkchi·Reza Mansouri
View original source ↗Read source document ↗Export metadata ↓

Abstract

We study the volume averaging of inhomogeneous metrics within GR and discuss its shortcomings such as gauge dependence, singular behavior as a result of caustics, and causality violations. To remedy these shortcomings, we suggest some modifications to this method. As a case study we focus on the inhomogeneous structured FRW model based on a flat LTB metric. The effect of averaging is then studied in terms of an effective backreaction fluid. It is shown that, contrary to the claims in the literature, the backreaction fluid behaves like a dark matter component, instead of dark energy, having a density of the order of 10^{-5} times the matter density, and most importantly, it is gauge dependent.

Explore related subjects

astro-ph

Keep this discovery

BibTeXRIS

Shahram Khosravi, Ehsan Kourkchi, Reza Mansouri. 2009-07-22. Modified Averaging Processes in Cosmology and the Structured FRW model. https://doi.org/10.1142/s0218271809015011

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2019

Classical analysis of the rotational dynamic of spiral galaxies: Quo Vadis Dark Matter?

In this paper we study a stellar dynamic model for the stars' rotational-dynamics, with a distribution of its own mass, rotating around its center with a higher density, like spiral galaxies happen, by means of a classical calculus of the rotation velocities of a particle around its rotational axis, inside a smoothed distribution of matter. The stars are supposed to be particles and their distribution in the galaxy is modelled as a matter distribution inversely proportional to its distance from its center. Two kinds of matter distribution are supposed: one with constant density, and other with radial distribution. Two types of galaxy symmetry are also considered: spherical and oblate ellipsoidal. Using only classical mechanics arguments it is shown that the calculated velocity distribution inside the galaxy is similar to that obtained from astronomical observations, without the necessity of suppose the existence of dark matter or other phenomena.

astro-ph↗
arXiv2019

AIRES: A system for air shower simulations

The AIRES (AIR-shower Extended Simulations) system is a set of programs and subroutines to realistically simulate particle showers produced after the incidence of high energy cosmic rays on the Earth's atmosphere, and to manage all the related output data. The current version includes a series of improvements with respect to previous releases that are explained in detail in this manual and/or the web site aires.fisica.unlp.edu.ar from where the software can be downloaded. Among such improvements, it is worth mentioning: (i) High energy hadronic collisions can be simulated usign the the well-known hadronic models EPOS, QGSJET, or SIBYLL, all of them in their LHC-tuned versions. (ii) Detailed simulation of unstable hadron decays. (iii) The inclusion of a series of pre-compiled, ready to use, external special particle modules, that are characteristic of AIRES since its early versions. Such modules allow, for example, to easily simulate multi-primary particle showers. (iv) An exhaustive revision of the atmospheric profile models, including annual average profiles for geographcal locations corresponding to currently in operation ultra-high energu shower observatories; and also the capability of accepting user-defined custom atmospheric profiles.

astro-ph↗
arXiv2019

A new paradigm for the universe

This book provides a completely new approach to understanding the universe. The main idea is that the principal objects in the universe form a spectrum unified by the presence of a massive or hypermassive black hole. These objects are variously called quasars, active galaxies and spiral galaxies. The key to understanding their dynamics is angular momentum and the key tool, and main innovative idea of this work, is a proper formulation of "Mach's principle" using Sciama's ideas. In essence, what is provided here is a totally new paradigm for the universe. In this paradigm, there is no big bang, and the universe is many orders of magnitude older than current estimates for its age. Indeed there is no natural limit for its age.

astro-ph↗