Generalized Brans-Dicke theories

Abstract

In Brans-Dicke theory a non-linear self interaction of a scalar field allows a possibility of realizing the late-time cosmic acceleration, while recovering the General Relativistic behavior at early cosmological epochs. We extend this to more general modified gravitational theories in which a de Sitter solution for dark energy exists without using a field potential. We derive a condition for the stability of the de Sitter point and study the background cosmological dynamics of such theories. We also restrict the allowed region of model parameters from the demand for the avoidance of ghosts and instabilities. A peculiar evolution of the field propagation speed allows us to distinguish those theories from the LCDM model.

14 pages, 4 figures, version to appear in JCAP

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• Imperfect Dark Energy from Kinetic Gravity Braiding
• G-inflation: inflation driven by the Galileon field
• Higgs G-inflation
• Observational constraints on Galileon cosmology
• Primordial non-Gaussianity from the DBI Galileons
• Matter perturbations in Galileon cosmology
• Primordial non-Gaussianities in general modified gravitational models of inflation
• Primordial non-Gaussianity from G-inflation
• Cosmology of the selfaccelerating third order Galileon
• Perturbations in Matter Bounce with Non-minimal Coupling
• Testing metric-affine f(R)-gravity by relic scalar gravitational waves