Effective description of higher-order scalar-tensor theories

By D. Langlois, Michele Mancarella, K. Noui, F. Vernizzi. 2017

180 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/3f7ec591adf5e87ab43164ff12c3012a328af447

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Citations in the corpus

Scalar-tensor theories and modified gravity in the wake of GW170817 (2017, background): “In fact, it is even more useful to consider the ADM form of the DHOST Lagrangian, also derived in [9] (in a gauge where the scalar field is spatially uniform), because it provides nonlinear information and thus makes the background-dependenteffects manifest.”
Dark Energy in Light of Multi-Messenger Gravitational-Wave Astronomy (2018, background): “Demanding the existence of a Poisson-like equation for the gravitational potential restricts the space of DHOST theories to those that are related to Horndeski via disformal transformations (9) (Langlois et al., 2017).”
hi_class: Horndeski in the Cosmic Linear Anisotropy Solving System (2016, unknown): “To this end future releases of hi_class will transcend the scope of Horndeski’s theory and include the full EFT of DE and its generalizations [92, 93].”
A systematic approach to generalisations of General Relativity and their cosmological implications (2018, background): “Using the language of effective description of dark energy [233, 234, 235] in terms of lapse, shift and the extrinsic curvature, the quadratic action for DHOST can be written as [236]”
Gravitational wave decay into dark energy (2018, background): “[46], for DHOST theories we find that neither αH nor β1, the coefficient parameterizing the presence of higher-order operators, vanish.”
Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review (2018, methodology): “For (quadratic and cubic) DHOST theories, the degeneracy conditions imply that the above parameters satisfy either one of the following sets of conditions [38]:”
Horndeski theory and beyond: a review (2019, background): “, either of the two modes is unstable), or tensor perturbations are nondynamical [169, 175].”
Effective field theory of dark energy: A review (2019, methodology): “[96, 97, 318, 319], the Kinetic Gravity Braiding model [93], the shift symmetric GLPV model [274], the tracking and scaling DHOST theories discussed in Ref.”