Cosmological investigations of (extended) nonlinear massive gravity schemes with non-minimal coupling

Abstract

In this paper we investigate the case of non-minimal coupling in the (extended) nonlinear massive gravity theories. We first consider massive gravity in the Brans-Dicke background such that the graviton mass is replaced by $A^2(σ)m$ where $σ$ is the Brans-Dicke field and $A(σ)$ is conformal coupling and show that there is no viable thermal history of the universe in this case. We then invoke a cubic galileon term as nonlinear completion of the $σ$ Lagrangian and show that there is a stable de Sitter solution in this case. However, the de Sitter is blocked by the matter phase which is also a simultaneous attractor of the dynamics. The de Sitter phase can, however, be realized by invoking unnatural fine tunings. We next investigate cosmology of quasi-dilaton nonlinear massive gravity with non-minimal coupling. As a generic feature of the non-minimal coupling, we show that the model exhibits a transient phantom phase which is otherwise impossible. While performing the observational data analysis on the models, we find that a small value of coupling constant is allowed for quasi-dilaton nonlinear massive gravity. For both the cases under consideration, it is observed that we have an effective pressure of matter which comes from the constraint equation. For mass-varying nonlinear massive gravity in the Brans-Dicke background, the effective pressure of matter is non zero which affects the evolution of the Hubble parameter thereby spoiling consistency of the model with data. As for, quasi-dilaton nonlinear massive gravity, the effective pressure of matter can be kept around zero by controlling the coupling constant, the model is shown to be fit well with observations.