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Observational constraints with recent data on the DGP modified gravity
, Article International Journal of Theoretical Physics ; Volume 48, Issue 4 , 2009 , Pages 1203-1230 ; 00207748 (ISSN) ; Farhang, M ; Rahvar, S ; Sharif University of Technology
2009
Abstract
We study one of the simplest covariant modified-gravity models based on the Dvali-Gabadadze-Porrati (DGP) brane cosmology, a self-accelerating universe. In this model gravitational leakage into extra dimensions is responsible of late-time acceleration. We mainly focus on the effects of the model parameters on the geometry and the age of universe. Also we investigate the evolution of matter density perturbations in the modified gravity model, and obtain an analytical expression for the growth index, f. We show that increasing Ωrcleads to less growth of the density contrast δ, and also decreases the growth index. We give a fitting formula for the growth index at the present time and indicate...
The Observational Tests of Dark Energy and Modified Gravity Theories
, Ph.D. Dissertation Sharif University of Technology ; Rahvar, Sohrab (Supervisor)
Abstract
The cosmological observations, like the luminosity distance of type Ia Supernovas, Cosmic Microwave Background radiation (CMB), Baryon Acoustic Oscillations (BAO) and Large Scale Structure (LSS) observations indicate that the Universe is nearly flat and also it is in a phase of acceleration. In the context of standard cosmological models, it means that the Universe is made of an unknown component (Dark Energy), which approximately has 70% of total energy-momentum of the Universe. The Cosmological Constant(CC) in the paradigm of ΛCDM model is the easiest model to describe the acceleration of the Universe. On the other hand the fine tuning (CC problem) and coincidence problems open new...