The parameter space in Galileon gravity models
  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 9-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 CMB data rather than the
CMB 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 WMAP 9-year results
better than the standard \Lambda-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 2\sigma\ in the Galileon
model compared with \Lambda CDM. We highlight other potential constraints of
the Galileon model using galaxy clustering and weak lensing measurements.
