Scalar mode propagation in modified gravity with a scalar field

Abstract

We study the propagation of the scalar modes around a Friedmann-Lemaitre-Robertson-Walker universe for general modifications of gravity in the presence of a real scalar field. In general, there will be two propagating scalar perturbation fields, which will have in total four degrees of freedom. Two of these degrees will have a superluminal propagation--with k-dependent speed of propagation--whereas the other two will travel with the speed of light. Therefore, the scalar degrees of freedom do not modify the general feature of modified gravity models: the appearance of modes whose frequency depends on the second power of the modulus of the wave vector. Constraints are given and special cases are discussed.

13 pages, 1 figure, uses RevTeX

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• Density perturbations in general modified gravitational theories
• Stability of Schwarzschild-like solutions in f(R,G) gravity models
• Regular black holes in $f(T)$ Gravity through a nonlinear electrodynamics source
• Generalized Brans-Dicke theories
• Cosmological perturbations of a perfect fluid and noncommutative variables
• Locally Rotationally Symmetric Bianchi Type-I cosmological model in $f(T)$ gravity: from early to Dark Energy dominated universe
• Cosmological perturbation in f(R,G) theories with a perfect fluid
• Observational constraints on non-minimally coupled Galileon model
• Spherical Accretion of Matter by Charged Black Holes on f(T) Gravity
• Perfect fluid in Lagrangian formulation due to generalized three-form field
• Supernova, baryon acoustic oscillations, and CMB surface distance constraints on f(G) higher order gravity models
• Bounds from ISW-galaxy cross-correlations on generalized covariant Galileon models
• Reconstructing $f(T)$ modified gravity from ECHDE and ECNADE models
• Scalar Mode Quadrupole Radiation from Astronomical Sources in $F(R)$ Modified Gravity