Generalized quasi-dilaton theory
  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.
