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Degenerate higher derivative theories beyond Horndeski: evading the Ostrogradski instability
Theories with higher order time derivatives generically suffer from ghost-like instabilities, known as Ostrogradski instabilities. This fate can be avoided by considering "degenerate" Lagrangians,Expand
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Healthy theories beyond Horndeski
Jérôme Gleyzes, 2 David Langlois, Federico Piazza, 4 and Filippo Vernizzi CEA, Institut de Physique Théorique, F-91191 Gif-sur-Yvette cédex, CNRS, Unité de recherche associée-2306, F-91191Expand
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Brane cosmological evolution in a bulk with cosmological constant
Abstract We consider the cosmology of a “3-brane universe” in a five dimensional (bulk) space-time with a cosmological constant. We show that Einstein's equations admit a first integral, analogous toExpand
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Exploring gravitational theories beyond Horndeski
We have recently proposed a new class of gravitational scalar-tensor theories free from Ostrogradski instabilities, in arXiv:1404.6495. As they generalize Horndeski theories, or "generalized"Expand
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Non-conventional cosmology from a brane-universe
Abstract We consider “brane universes”, where energy density is confined to four-dimensional hypersurfaces (three-branes) whereas one extra compact dimension is felt by gravity only. We show that theExpand
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Hamiltonian formalism and gauge invariance for linear perturbations in inflation
A Hamiltonian treatment of gauge-invariant cosmological perturbations is presented. In this framework the gauge-invariant perturbations as well as their evolution equations are obtained with minimalExpand
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Essential Building Blocks of Dark Energy
We propose a minimal description of single field dark energy/modified gravity within the effective field theory formalism for cosmological perturbations, which encompasses most existing models. WeExpand
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Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations
We consider all degenerate scalar-tensor theories that depend quadratically on second-order derivatives of a scalar field, which we have identified in a previous work. These theories, whoseExpand
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Curvature and isocurvature perturbations in two-field inflation
We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, upExpand
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A unifying description of dark energy
We review and extend a novel approach that we introduced recently, to describe general dark energy or scalar-tensor models. Our approach relies on an ADM formulation based on the hypersurfaces whereExpand
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