Cosmological data favor Galileon ghost condensate over ΛCDM

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 cubic covariant Galileon by taking an additional higher-order field derivative X 2 into account. This allows for the dark energy equation of state wDE to access the region −2 < wDE < −1 avoinding ghosts. Indeed, this peculiar evolution of wDE is favored over that of the cosmological constant Λ (wDE = −1) from the joint data analysis of cosmic microwave background (CMB) radiation, baryonic acoustic oscillations, supernovae type Ia and redshift-space distortions. Furthermore, our model exhibits a better compatibility with the CMB data over the Λ-cold-darkmatter (ΛCDM) model by suppressing large-scale temperature anisotropies. We perform a model selection analysis by using several methods and find a statistically significant preference of the Galileon ghost condensate model over ΛCDM.

Effective field theory of dark energy: A review

“…A phenomenological analysis shows that interestingly the low-ISW tail is lower than in the standard ΛCDM scenario for x 3 x 2 [137]. Another relevant feature is that the equation of state of DE can be in the region −2 < w DE < −1 at low redshifts [274].…”

“…The set of EFT functions used in EFTCAMB is in Appendix B (we refer to it as EFTCAMB basis hereafter). The code has built-in models which include specific theories such as designer f (R)-gravity [68], f (R)-Hu Sawicki model [134], minimally coupled quintessence [80], low-energy Hořava gravity [45], covariant Galileon [135], K-mouflage [136], Galileon Ghost Condensate [137], beyond Horndeski model [138] as well as several model-independent parameterizations of the DE equation of state and choices for the EFT functions. It allows to use the α-basis as well [122].…”

“…where a 1,2,3 are constants. The model is implemented in EFTCAMB [137] and for convenience the following dimensionless variables are considered on a FLRW background…”

“…Another relevant feature is that the equation of state of DE can be in the region −2 < w DE < −1 at low redshifts [274]. The constraints on the present day values of the above parameters using a combination of CMB, BAO, RSD and SNIa data [137] yield: x 2 . Finally, according to the Deviance Information Criterion (DIC) [276] and the Bayesian evidence factor (log 10 B) [277,278], the GGC model is found to be statistically preferred over ΛCDM even with additional model parameters.…”

Phenomenology of the generalized cubic covariant Galileon model and cosmological bounds

“…One of the most studied proposal of MG is the Horndeski theory (or Galileon theory) [11,12], characterized by the presence of four free functions, namely [G 2 , G 3 , G 4 , G 5 ][φ, X], where φ is the extra scalar field, whose dynamics is settled by second order equations of motion, and X = ∂ µ φ∂ µ φ. Recently, a proposal in cubic-order Horndeski theories, the Galileon ghost condensate model [13], showed to be statistically preferred over the standard ΛCDM scenario due to a suppression in the integrated-Sachs-Wolfe (ISW) tail and a different behaviour in the expansion history [14]. Another promising proposal is the generalized covariant Galileon model [15], which extends the covariant Galileon [16] by considering in the Lagrangians power laws functions of X (G i ∝ X p i , where p i are free constant parameters).…”