Generalized quasi-dilaton theory

TL;DR

This paper extends the quasidilaton theory of Lorentz-invariant massive gravity by adding general Lagrangian terms that preserve symmetry and second-order equations, without altering the core structure of the stable model.

Contribution

It introduces a generalized quasidilaton action with additional symmetry-compatible terms, maintaining the stability and structure of the original theory.

Findings

The generalized action preserves the stability of de Sitter solutions.

The theory's structure remains unchanged despite new Lagrangian terms.

Second order equations of motion are maintained.

Abstract

Recently the first example of a unitary theory of Lorentz-invariant massive gravity allowing for stable self-accelerating de Sitter solutions was found, extending the quasidilaton theory. In this paper we further generalize this new action for the quasidilaton field by introducing general Lagrangian terms which are consistent with the quasidilaton symmetry while leading to second order equations of motion. We find that the structure of the theory, compared to the simplest stable example, does not change on introducing these new terms.