N-body simulations of γ gravity

¹ Instituto de Física, Universidade Federal do Rio de Janeiro C P 68528, CEP 21941-972, Rio de Janeiro, RJ, Brazil
e-mail: vargas@if.ufrj.br; ioav@if.ufrj.br
² Institute of Theoretical Astrophysics, University of Oslo, Postboks 1029, 0315 Oslo, Norway
e-mail: d.f.mota@astro.uio.no
³ Astrophysics, University of Oxford, DWB, Keble Road, Oxford, OX1 3RH, UK
e-mail: hans.a.winther@gmail.com

Received: 26 October 2015
Accepted: 11 January 2016

Abstract

We have investigated structure formation in the γ gravity f(R) model with N-body simulations. The γ gravity model is a proposal which, unlike other viable f(R) models, not only changes the gravitational dynamics, but can in principle also have signatures at the background level that are different from those obtained in ΛCDM (Cosmological constant, Cold Dark Matter). The aim of this paper is to study the nonlinear regime of the model in the case where, at late times, the background differs from ΛCDM. We quantify the signatures produced on the power spectrum, the halo mass function, and the density and velocity profiles. To appreciate the features of the model, we have compared it to ΛCDM and the Hu-Sawicki f(R) models. For the considered set of parameters we find that the screening mechanism is ineffective, which gives rise to deviations in the halo mass function that disagree with observations. This does not rule out the model per se, but requires choices of parameters such that | f_R0 | is much smaller, which would imply that its cosmic expansion history cannot be distinguished from ΛCDM at the background level.