Curvature perturbations of quasidilaton non-linear massive gravity

TL;DR

This paper analyzes the cosmological perturbations in an extended non-linear massive gravity theory with a scalar field, revealing unique superhorizon behavior and constraints on the model's parameters.

Contribution

It introduces a scalar field extension that adds a new symmetry and explores its impact on cosmological perturbations and gravitational wave properties.

Findings

Tensor modes have a time-dependent mass affecting gravitational wave dispersion.

Superhorizon curvature perturbations always grow, not remain constant.

Parameter space is restricted by the consistency of the perturbation equations.

Abstract

We study the cosmological perturbations of the recently proposed extension of non-linear massive gravity with a scalar field. The added scalar field ensures a new symmetry on the field space of the theory. The theory has the property of having a flat dS solution, in contrast to the standard dRGT massive gravity. The tensor part is the same as that of the standard dRGT and shows gravitational waves with a time dependent mass which modifies the dispersion relation. We obtain the curvature perturbation of the model on superhorizon scales for a specific choice of $\omega=0$ and find that the theory does not allow a constant curvature perturbation on the superhorizon scales and we have always a growing mode. The consistency of equations restricts the parameter space of the theory.