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 X-2 into account. This allows for the dark energy equation of state w(DE) to access the region -2 < w(DE) < -1 without ghosts. Indeed, this peculiar evolution of w(DE) is favored over that of the cosmological constant Lambda 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 Lambda-cold-dark-matter (Lambda CDM) model by suppressing large-scale temperature anisotropies. The CMB temperature and polarization data lead to an estimation for today's Hubble parameter H-0 consistent with its direct measurements at 2 sigma. We perform a model selection analysis by using several methods and find a statistically significant preference of the Galileon ghost condensate model over Lambda CDM.