Search

We present the first constraints on the full parameter space of the Galileon modified gravity model, considering both the cosmological parameters and the coefficients which specify the additional terms in the Lagrangian due to the Galileon field, which we call the Galileon parameters. We use the latest cosmic microwave background measurements, along with distance measurements from supernovae and baryonic acoustic oscillations, performing a Monte Carlo Markov Chain exploration of the nine-dimensional parameter space. The integrated Sachs-Wolfe signal can be very different in Galileon models compared to standard gravity, making it essential to use the full cosmic microwave background data rather than the cosmic microwave background distance priors. We demonstrate that meaningful constraints are only possible in the Galileon parameter space after taking advantage of a scaling degeneracy. We find that the Galileon model can fit the Wilkinson microwave anisotropy probe 9-year results better than the standard ?-cold dark matter model, but gives a slightly worse fit overall once lower redshift distance measurements are included. The best-fitting cosmological parameters (e.g., matter density, scalar spectral index, fluctuation amplitude) can differ by more than 2σ in the Galileon model compared with ACDM. We highlight other potential constraints of the Galileon model using galaxy clustering and weak lensing measurements. [ABSTRACT FROM AUTHOR]

We study the cosmology of Galileon modified gravity models in the linear perturbation regime. We derive the fully covariant and gauge invariant perturbed field equations using two different methods, which give consistent results, and solve them using a modified version of the CAMB code. We find that, in addition to modifying the background expansion history and therefore shifting the positions of the acoustic peaks in the cosmic microwave background power spectrum, the Galileon field can cluster strongly from early times, and causes the Weyl gravitational potential to grow, rather than decay, at late times. This leaves clear signatures in the low-/ cosmic microwave background power spectrum through the modified integrated Sachs-Wolfe effect, strongly enhances the linear growth of matter density perturbations and makes distinctive predictions for other cosmological signals such as weak lensing and the power spectrum of density fluctuations. The quasistatic approximation is shown to work quite well from small to the near-horizon scales. We demonstrate that Galileon models display a rich phenomenology due to the large parameter space and the sensitive dependence of the model predictions on the Galileon parameters. Our results show that some Galileon models are already ruled out by present data and that future higher significance galaxy clustering, integrated Sachs-Wolfe, and lensing measurements will place strong constraints on Galileon gravity. [ABSTRACT FROM AUTHOR]

We perform a validation of estimates of the growth rate of structure, described by the parameter combination fσ8, in modified gravity cosmologies. We consider an analysis pipeline based on the redshift-space distortion modeling of the clustering wedges statistic of the galaxy correlation function and apply it to mock catalogues of Lambda cold dark matter (ΛCDM) and the normal branch of Dvali-Gabadadze-Porrati (DGP) cosmologies. We employ a halo occupation distribution approach to construct our mocks, which we ensure resemble the CMASS sample from Baryon Oscillation Spectroscopic Survey (BOSS) in terms of the total galaxy number density and large-scale amplitude of the power spectrum monopole. We show that the clustering wedges model successfully recovers the true growth rate difference between DGP and ΛCDM, even for cases with over 40% enhancement in fσ8 compared to ΛCDM. The unbiased performance of the clustering wedges model allows us to use the growth rate values estimated from the BOSS DR12 data to constrain the crossover scale rc of DGP gravity to [rcH0]-1<0.97 (2σ) or rc>3090 Mpc/h, cutting into the interesting region of parameter space with rc ~H-10 using constraints from the growth of structure alone. [ABSTRACT FROM AUTHOR]