Cosmological constraints on extended Galileon models

TL;DR

This paper investigates extended Galileon models with tracker solutions, constrains their parameters using cosmological observations, and explores their effects on large-scale structure and CMB anisotropies.

Contribution

It provides observational constraints on extended Galileon models, including their parameter s, and analyzes their impact on large-scale structure and CMB correlations.

Findings

Parameter s constrained to 0.034 (-0.034,+0.327) at 95% CL

LSS and ISW effects can be positively or negatively correlated depending on model parameters

Viable parameter spaces are identified where ghosts and instabilities are absent

Abstract

The extended Galileon models possess tracker solutions with de Sitter attractors along which the dark energy equation of state is constant during the matter-dominated epoch, i.e. w_DE = -1-s, where s is a positive constant. Even with this phantom equation of state there are viable parameter spaces in which the ghosts and Laplacian instabilities are absent. Using the observational data of the supernovae type Ia, the cosmic microwave background (CMB), and baryon acoustic oscillations, we place constraints on the tracker solutions at the background level and find that the parameter s is constrained to be s=0.034 (-0.034,+0.327) (95% CL) in the flat Universe. In order to break the degeneracy between the models we also study the evolution of cosmological density perturbations relevant to the large-scale structure (LSS) and the Integrated-Sachs-Wolfe (ISW) effect in CMB. We show that, depending on the model parameters, the LSS and the ISW effect is either positively or negatively correlated. It is then possible to constrain viable parameter spaces further from the observational data of the ISW-LSS cross-correlation as well as from the matter power spectrum.