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Effects of Nonlinear Inhomogeneity on the Cosmic Expansion with Numerical Relativity

Eloisa Bentivegna and Marco Bruni
Phys. Rev. Lett. 116, 251302 – Published 24 June 2016
Physics logo See Synopsis: A Relativistic View of a Clumpy Universe

Abstract

We construct a three-dimensional, fully relativistic numerical model of a universe filled with an inhomogeneous pressureless fluid, starting from initial data that represent a perturbation of the Einstein–de Sitter model. We then measure the departure of the average expansion rate with respect to this homogeneous and isotropic reference model, comparing local quantities to the predictions of linear perturbation theory. We find that collapsing perturbations reach the turnaround point much earlier than expected from the reference spherical top-hat collapse model and that the local deviation of the expansion rate from the homogeneous one can be as high as 28% at an underdensity, for an initial density contrast of 102. We then study, for the first time, the exact behavior of the backreaction term QD. We find that, for small values of the initial perturbations, this term exhibits a 1/a scaling, and that it is negative with a linearly growing absolute value for larger perturbation amplitudes, thereby contributing to an overall deceleration of the expansion. Its magnitude, on the other hand, remains very small even for relatively large perturbations.

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  • Received 7 December 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.251302

© 2016 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Synopsis

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A Relativistic View of a Clumpy Universe

Published 24 June 2016

Cosmologists have begun using fully relativistic models to understand the effects of inhomogeneous matter distribution on the evolution of the Universe.

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Authors & Affiliations

Eloisa Bentivegna1,2,* and Marco Bruni3

  • 1Dipartimento di Fisica e Astronomia, Università degli Studi di Catania, Via Santa Sofia 64, 95123 Catania, Italy
  • 2INFN, Sezione di Catania, Via Santa Sofia 64, 95123 Catania, Italy
  • 3Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX, United Kingdom

  • *Corresponding author. eloisa.bentivegna@unict.it

See Also

Departures from the Friedmann-Lemaitre-Robertston-Walker Cosmological Model in an Inhomogeneous Universe: A Numerical Examination

John T. Giblin, Jr., James B. Mertens, and Glenn D. Starkman
Phys. Rev. Lett. 116, 251301 (2016)

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Vol. 116, Iss. 25 — 24 June 2016

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