Jason Dossett, Mustapha Ishak, Jacob Moldenhauer
The testing of general relativity at cosmological scales has become a
possible and timely endeavor that is not only motivated by the pressing
question of cosmic acceleration but also by the proposals of some extensions to
general relativity that would manifest themselves at large scales of distance.
We analyze here correlations between modified gravity growth parameters and
some core cosmological parameters using the latest cosmological data sets
including the refined COSMOS 3D weak lensing. We provide the parameterized
modified growth equations and their evolution. We implement known functional
and binning approaches, and propose a new hybrid approach to evolve the
modified gravity parameters in redshift (time) and scale. The hybrid
parameterization combines a binned redshift dependence and a smooth evolution
in scale avoiding a jump in the matter power spectrum. The formalism developed
to test the consistency of current and future data with general relativity is
implemented in a package that we make publicly available and call ISiTGR
(Integrated Software in Testing General Relativity), an integrated set of
modified modules for the publicly available packages CosmoMC and CAMB,
including a modified version of the ISW-galaxy cross correlation module of Ho
et al and a new weak-lensing likelihood module for the refined HST-COSMOS weak
gravitational lensing tomography data. We obtain parameter constraints and
correlation coefficients finding that modified gravity parameters are
significantly correlated with \sigma_8 and mildly correlated with \Omega_m, for
all evolution methods. The degeneracies between \sigma_8 and modified gravity
parameters are found to be substantial for the functional form and also for
some specific bins in the hybrid and binned methods indicating that these
degeneracies will need to be taken into consideration when using future high
precision data.
View original:
http://arxiv.org/abs/1109.4583
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