Extended dRGT massive gravity via cubic Galileon

There are many models that describe graviton and its interactions. However, finding a stable and observationally consistent theory that explains a massive spin-2 field remains a major concern. Recently, de Rham, Gabadadze, and Tolley constructed a ghost-free nonlinear massive gravity theory called dRGT massive gravity. Although this avoids the Boulware-Deser ghost associated with the nonlinear Pauli-Fierz theory, the dRGT massive gravity has instabilities in FLRW homogeneous spacetime. One way to resolve this problem is to couple an additional scalar field to the background, known as quasi-dilaton massive gravity. In this talk, we introduce an extension to dRGT massive gravity by a generalized quasi-dilaton theory in which the scalar field coupled to the graviton is a cubic Galileon and present the cosmology of this theory. We analyze the self-accelerating background solutions to explain the late-time acceleration of the Universe. We examine the cubic Galileon massive gravity via the latest Union2 Type Ia Supernovae (SNIa) dataset and show that the model is compatible with the observations. We also present a tensor perturbation analysis and obtain the dispersion relation of gravitational waves in this theory.