# Cosmological data favor Galileon ghost condensate over $\Lambda$CDM

## TL;DR

This study shows that the Galileon ghost condensate model, a dark energy theory compatible with gravitational wave observations, fits cosmological data better than the standard $\Lambda$CDM model, especially in explaining the universe's accelerated expansion.

## Contribution

The paper introduces observational constraints on an extended Galileon ghost condensate model, demonstrating its improved fit to cosmological data over $\Lambda$CDM, including better CMB compatibility and a preferred dark energy equation of state.

## Key findings

- Galileon ghost condensate model fits data better than $\Lambda$CDM.
- Model favors $w_{DE}$ in the range -2 to -1, unlike cosmological constant.
- Estimates current Hubble parameter consistent with direct measurements.

## Abstract

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 $w_{\rm DE}$ to access the region $-2<w_{\rm DE}<-1$ without ghosts. Indeed, this peculiar evolution of $w_{\rm DE}$ 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.