Cosmological data favor Galileon ghost condensate over ΛcDM

We place observational constraints on the Galileon ghost condensate model, a dark energy proposal in cubic-order Horndeski theories consistent with the gravitational-wave event GW170817. The model extends the covariant Galileon by taking an additional higher-order field derivative X2 into account. This allows for the dark energy equation of state wDE to access the region -2<wDE<-1 without ghosts. Indeed, this peculiar evolution of wDE is favored over that of the cosmological constant Λ from the joint data analysis of cosmic microwave background (CMB) radiation, baryonic acoustic oscillations (BAOs), supernovae type Ia (SNIa), and redshift-space distortions (RSDs). Furthermore, our model exhibits a better compatibility with the CMB data over the Λ-cold-dark-matter (ΛCDM) model by suppressing large-scale temperature anisotropies. The CMB temperature and polarization data lead to an estimation for today's Hubble parameter H0 consistent with its direct measurements at 2σ. We perform a model selection analysis by using several methods and find a statistically significant preference of the Galileon ghost condensate model over ΛCDM.