Most existing theories of dark energy and/or modified gravity, involving a scalar degree of freedom, can be conveniently described within the framework of the Effective Theory of Dark Energy, based on the unitary gauge where the scalar field is uniform. We extend this effective approach by allowing the Lagrangian in unitary gauge to depend on the time derivative of the lapse function. Although this dependence generically signals the presence of an extra scalar degree of freedom, theories that contain only one propagating scalar degree of freedom, in addition to the usual tensor modes, can be constructed by requiring the initial Lagrangian to be degenerate. Starting from a general quadratic action, we derive the dispersion relations for the linear perturbations around Minkowski and a cosmological background. Our analysis directly applies to the recently introduced Degenerate Higher-Order Scalar-Tensor (DHOST) theories. For these theories, we find that one cannot recover a Poisson-like equation in the static linear regime except for the subclass that includes the Horndeski and so-called "beyond Horndeski" theories. We also discuss Lorentz-breaking models inspired by Horava gravity.

Langlois, D., Mancarella, M., Noui, K., Vernizzi, F. (2017). Effective description of higher-order scalar-tensor theories. JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2017(5) [10.1088/1475-7516/2017/05/033].

Effective description of higher-order scalar-tensor theories

Mancarella M.;
2017

Abstract

Most existing theories of dark energy and/or modified gravity, involving a scalar degree of freedom, can be conveniently described within the framework of the Effective Theory of Dark Energy, based on the unitary gauge where the scalar field is uniform. We extend this effective approach by allowing the Lagrangian in unitary gauge to depend on the time derivative of the lapse function. Although this dependence generically signals the presence of an extra scalar degree of freedom, theories that contain only one propagating scalar degree of freedom, in addition to the usual tensor modes, can be constructed by requiring the initial Lagrangian to be degenerate. Starting from a general quadratic action, we derive the dispersion relations for the linear perturbations around Minkowski and a cosmological background. Our analysis directly applies to the recently introduced Degenerate Higher-Order Scalar-Tensor (DHOST) theories. For these theories, we find that one cannot recover a Poisson-like equation in the static linear regime except for the subclass that includes the Horndeski and so-called "beyond Horndeski" theories. We also discuss Lorentz-breaking models inspired by Horava gravity.
Articolo in rivista - Articolo scientifico
cosmological perturbation theory; dark energy theory; modified gravity;
English
2017
2017
5
033
none
Langlois, D., Mancarella, M., Noui, K., Vernizzi, F. (2017). Effective description of higher-order scalar-tensor theories. JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, 2017(5) [10.1088/1475-7516/2017/05/033].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/400835
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