27 research outputs found
Cosmological perturbations in massive gravity with doubly coupled matter
We investigate the cosmological perturbations around FLRW solutions to non- linear massive gravity with a new effective coupling to matter proposed recently. Unlike the case with minimal matter coupling, all five degrees of freedom in the gravity sector propagate on generic self-accelerating FLRW backgrounds. We study the stability of the cosmological solutions and put constraints on the parameters of the theory by demanding the correct sign for the kinetic terms for scalar, vector and tensor perturbations
New symmetries in Fierz-Pauli massive gravity
We expose a new symmetry for linear perturbations around a solution of
non-linear Fierz-Pauli massive gravity plus a bare cosmological constant. The
cosmological constant is chosen such that the background metric is flat while
the Stuckelberg fields have a non-trivial profile. Around this background, at
linear order the new symmetry reduces the propagating degrees of freedom to
those of General Relativity, namely the massless helicity 2 modes only. We
discuss the physical consequences and possible applications of these findings.Comment: 9 pages, no figure
Comments About Hamiltonian Formulation of Non-Linear Massive Gravity with Stuckelberg Fields
We perform the Hamiltonian analysis of some form of the non-linear massive
gravity action that is formulated in the Stuckelberg formalism. Following
seminal analysis performed in arXiv:1203.5283 [hep-th] we find that this theory
possesses one primary constraint which could eliminate one additional mode in
this theory. We performed the explicit Hamiltonian analysis of two dimensional
non-linear massive gravity and we found that this is theory free from the
ghosts.Comment: 17 pages,v2:typos corrected, references added, v3. Rewritten the main
body of the paper after publication of the paper arXiv:1203.5283 [hep-th]
where the primary constraint was identified so that the conclusion is
different from the first version of the paper. It is also version that is
accepted for publication in JHEP. arXiv admin note: substantial text overlap
with arXiv:1202.5899, arXiv:1204.2957, arXiv:1109.305
Cosmic acceleration from Abelian symmetry breaking
We discuss a consistent theory for a self-interacting vector field, breaking an Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal polarization. In an appropriate decoupling limit, the dynamics of the longitudinal mode is controlled by Galileon interactions. The full theory away from the decoupling limit does not propagate ghost modes, and can be investigated in regimes where non-linearities become important. When coupled to gravity, this theory provides a candidate for dark energy, since it admits de Sitter cosmological solutions characterized by a technically natural value for the Hubble parameter. We also consider the homogeneous evolution when, besides the vector, additional matter in the form of perfect fluids is included. We find that the vector can have an important role in characterizing the universe expansion
Confirmation of the Secondary Constraint and Absence of Ghost in Massive Gravity and Bimetric Gravity
In massive gravity and in bimetric theories of gravity, two constraints are
needed to eliminate the two phase-space degrees of freedom of the
Boulware-Deser ghost. For recently proposed non-linear theories, a Hamiltonian
constraint has been shown to exist and an associated secondary constraint was
argued to arise as well. In this paper we explicitly demonstrate the existence
of the secondary constraint. Thus the Boulware-Deser ghost is completely absent
from these non-linear massive gravity theories and from the corresponding
bimetric theories.Comment: 15 page
On Consistent Theories of Massive Spin-2 Fields Coupled to Gravity
We consider the issues that arise out of interpreting the ghost-free bimetric
theory as a theory of a spin-2 field coupled to gravity. This requires
identifying a gravitational metric and parameterizing deviations of the
resulting theory from general relativity. To this end, we first consider the
most general bimetric backgrounds for which a massless and a massive spin-2
fluctuation with Fierz-Pauli mass exist. These backgrounds coincide with
solutions in general relativity. Based on this, we obtain nonlinear extensions
of the massive and massless spin-2 fields. The background value of the
nonlinear massive field parameterizes generic deviations of the bimetric theory
from GR. It is also shown that the nonlinear massless field does not have
standard ghost-free matter couplings, and hence cannot represent the
gravitational metric. However, an appropriate gravitational metric can still be
identified in the weak gravity limit. Hence in the presence of other neutral
spin-2 fields, the weak gravity limit is crucial for compatibility with general
relativity. We also write down the action in terms of the nonlinear massive
spin-2 field and obtain its ghost-free couplings to matter. The discussion is
then generalized to multimetric theories.Comment: Latex, 31 page