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A unifying approach to dark energy models

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Recording Details

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This talk  will present  an effective  description of  single field dark energy/modified gravity models, which encompasses most  existing proposals.  The starting point is a generic Lagrangian expressed in terms of the lapse  and of the extrinsic and intrinsic curvature tensors of the uniform scalar field hypersurfaces. By expanding this Lagrangian up to quadratic order, one can describe the homogeneous background and the dynamics of  linear perturbations. In particular, one can identify seven Lagrangian operators that lead  to  equations of motion containing at most second order derivatives, the time-dependent coefficients  of three of these operators characterizing  the background evolution. I will illustrate this approach with  Horndeski's---or generalized Galileon---theories. Finally,  I will discuss  the link between this effective approach and  observations.