Revisiting perturbations in extended quasidilaton massive gravity

TL;DR

This paper analyzes the stability of cosmological perturbations in extended quasidilaton massive gravity with matter, providing refined constraints on model parameters for stable universe expansion solutions.

Contribution

It offers a detailed study of perturbation stability in the full dynamical background, improving upon previous approximations and enabling better comparison with observational data.

Findings

Tensor, vector, and scalar perturbations have different stability constraints.

Stable FLRW solutions can be identified within a restricted parameter space.

The results refine previous stability conditions by considering the full dynamical background.

Abstract

In this work we study the theory of extended quasidilaton massive gravity together with the presence of matter fields. After discussing the homogeneous and isotropic fully dynamical background equations, which governs the exact expansion history of the universe, we consider small cosmological perturbations around these general FLRW solutions. The stability of tensor, vector and scalar perturbations on top of these general background solutions give rise to slightly different constraints on the parameters of the theory than those obtained in the approximative assumption of the late-time asymptotic form of the expansion history, which does not correspond to our current epoch. This opens up the possibility of stable FLRW solutions to be compared with current data on cosmic expansion with the restricted parameter space based on theoretical ground.