Browsing by Author "Matarrese, Sabino"

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    Matter bispectrum in cubic Galileon cosmologies
    (IOP Science, 2013) Bartolo, Nicola; Bellini, Emilio; Bertacca, Daniele; Matarrese, Sabino
    In this paper we obtain the bispectrum of dark matter density perturbations in the frame of covariant cubic Galileon theories. This result is obtained by means of a semi- analytic approach to second-order perturbations in Galileon cosmologies, assuming Gaussian initial conditions. In particular, we show that, even in the presence of large deviations of the linear growth-rate w.r.t. the CDM one, at the bispectrum level such deviations are reduced to a few percent.
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    Testing gravity using large-scale redshift-space distortions
    (Oxford University Press, 2013) Raccanelli, Alvise; Bertacca, Daniele; Pietrobon, Davide; Schmidt, Fabian; Samushia, Lado; Bartolo, Nicola; Doré, Olivier; Matarrese, Sabino; Percival, Will J.
    We use luminous red galaxies from the Sloan Digital Sky Survey (SDSS) II to test the cosmological structure growth in two alternatives to the standard cold dark matter ( CDM)+general relativity (GR) cosmological model. We compare observed threedimensional clustering in SDSS Data Release 7 (DR7) with theoretical predictions for the standard vanilla CDM+GR model, unified dark matter (UDM) cosmologies and the normal branch Dvali–Gabadadze–Porrati (nDGP). In computing the expected correlations in UDM cosmologies, we derive a parametrized formula for the growth factor in these models. For our analysis we apply the methodology tested in Raccanelli et al. and use the measurements of Samushia et al. that account for survey geometry, non-linear and wide-angle effects and the distribution of pair orientation. We show that the estimate of the growth rate is potentially degenerate with wide-angle effects, meaning that extremely accurate measurements of the growth rate on large scales will need to take such effects into account. We use measurements of the zeroth and second-order moments of the correlation function from SDSS DR7 data and the Large Suite of Dark Matter Simulations (LasDamas), and perform a likelihood analysis to constrain the parameters of the models. Using information on the clustering up to rmax = 120 h−1 Mpc, and after marginalizing over the bias, we find, for UDM models, a speed of sound c∞ ≤ 6.1e-4, and, for the nDGP model, a cross-over scale rc ≥ 340 Mpc, at 95 per cent confidence level.