First experimental constraints on the disformally coupled Galileon model

Abstract

Aims. The Galileon model is a modified gravity model that can explain the late-time accelerated expansion of the Universe. In a previous work, we derived experimental constraints on the Galileon model with no explicit coupling to matter and showed that this model agrees with the most recent cosmological data. In the context of braneworld constructions or massive gravity, the Galileon model exhibits a disformal coupling to matter, which we study in this paper. Methods. After comparing our constraints on the uncoupled model with recent studies, we extend the analysis framework to the disformally coupled Galileon model and derive the first experimental constraints on that coupling, using precise measurements of cosmological distances and the growth rate of cosmic structures. Results. In the uncoupled case, with updated data, we still observe a low tension between the constraints set by growth data and those from distances. In the disformally coupled Galileon model, we obtain better agreement with data and favour a non-zero disformal coupling to matter at the 2.5σ level. This gives an interesting hint of the possible braneworld origin of Galileon theory.

Beyond the cosmological standard model

“…Cosmological parameter analyses to test MG theories have been performed by several authors [340,884,895,896,903,[908][909][910][911][912][913]. Specific studies to determine the cosmological impact of galileon theories and to constrain model parameters appear in [265,[914][915][916][917][918][919][920].…”

The observational status of Galileon gravity after Planck

“…We found that the amplitude of the low-l region of the CMB power spectrum, which is mostly determined by the Integrated Sachs-Wolfe (ISW) effect, plays a decisive role in constraining the parameter space of the Galileon model. The use of the full shape of the CMB temperature data results in much tighter constraints than those obtained by using only the information encoded in the CMB distance priors [16]. Reference [28] finds that the bestfitting Galileon models to the WMAP9 data [51] have a lower ISW power relative to ΛCDM, which results in a better fit.…”

“…References [20,21] explored the phenomenology of the Galileon model at the background level, and derived observational constraints using data from type 1 See, e.g., Refs. [13][14][15][16][17][18][19] for studies of models motivated in similar ways.…”

Parameter space in Galileon gravity models

“…The way the background cosmological evolution can be affected in Galileon models has already been studied and constrained using observational probes of the geometry of the Universe, such as type Ia supernovae (SNIa), the scale of the baryonic acoustic oscillations (BAO) feature in the galaxy distribution and the position of the peaks of the cosmic microwave background (CMB) angular power spectrum of temperature fluctuations [65][66][67][68][69][70][71]. Furthermore, by studying the evolution of density fluctuations in linear perturbation theory, it has also been shown how Galileon models can be constrained theoretically, by the imposition of conditions to avoid the presence of ghosts and other pathologies [67,69], and observationally, by investigating the predictions for the growth rate of large scale structure [70][71][72][73] and for the full CMB, linear matter and weak lensing potential power spectra [74] (see also [75] for a study of the bispectrum of the matter fluctuations).…”