Cosmological perturbation in f(R,G) theories with a perfect fluid

Abstract

In order to classify modified gravity models according to their physical properties, we analyze the cosmological linear perturbations for f(R,G) theories (R being the Ricci scalar and G, the Gauss-Bonnet term) with a minimally coupled perfect fluid. For the scalar type perturbations, we identify in general six degrees of freedom. We find that two of these physical modes obey the same dispersion relation as the one for a non-relativistic de Broglie wave. This means that spacetime is either highly unstable or its fluctuations undergo a scale-dependent super-luminal propagation. Two other modes correspond to the degrees of freedom of the perfect fluid, and propagate with the sound speed of such a fluid. The remaining two modes correspond to the entropy and temperature perturbations of the perfect fluid, and completely decouple from the other modes for a barotropic equation of state. We then provide a concise condition on f(R,G) theories, that both f(R) and R+f(G) do fulfill, to avoid the de Broglie type dispersion relation. For the vector type perturbation, we find that the perturbations decay in time. For the tensor type perturbation, the perturbations can be either super-luminal or sub-luminal, depending on the model. No-ghost conditions are also obtained for each type of perturbation.

12 pages, uses RevTeX

References in corpus (23)

• f(R) theories
• Models of f(R) Cosmic Acceleration that Evade Solar-System Tests
• Disappearing cosmological constant in f(R) gravity
• Dark energy in modified Gauss-Bonnet gravity: late-time acceleration and the hierarchy problem
• Conditions for the cosmological viability of f(R) dark energy models
• The Large Scale Structure of f(R) Gravity
• Observational signatures of f(R) dark energy models that satisfy cosmological and local gravity constraints
• Constraining f(R) Gravity as a Scalar Tensor Theory
• Construction of cosmologically viable f(G) gravity models
• The Cosmology of f(R) Gravity in the Metric Variational Approach
• The Cosmology of Modified Gauss-Bonnet Gravity
• Cosmology and Astrophysical Constraints of Gauss-Bonnet Dark Energy
• Stability of Cosmological Solution in f(R) Models of Gravity
• Gauss-Bonnet Quintessence: Background Evolution, Large Scale Structure and Cosmological Constraints
• The evolution of density perturbations in f(R) gravity
• Ghosts, Instabilities, and Superluminal Propagation in Modified Gravity Models
• Solar system constraints on f(G) gravity models
• Ghost conditions for Gauss-Bonnet cosmologies
• Vacuum structure for scalar cosmological perturbations in Modified Gravity Models
• Matter instabilities in general Gauss-Bonnet gravity
• Cosmological perturbations of a perfect fluid and noncommutative variables
• Superluminality in DGP
• Scalar mode propagation in modified gravity with a scalar field

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