Extended scalar-tensor theories of gravity

By M. Crisostomi, K. Koyama, G. Tasinato. 2016

389 citations recorded by the source corpus.

We study new consistent scalar-tensor theories of gravity recently introduced by Langlois and Noui with potentially interesting cosmological applications. We derive the conditions for the existence of a primary constraint that prevents the propagation of an additional dangerous mode associated with higher order equations of motion. We then classify the most general, consistent scalar-tensor theories that are at most quadratic in the second derivatives of the scalar field. In addition, we investigate the possible connection between these theories and (beyond) Horndeski through conformal and disformal transformations. Finally, we point out that these theories can be associated with new operators in the effective field theory of dark energy, which might open up new possibilities to test dark energy models in future surveys.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Oceanography

View Paper: https://www.semanticscholar.org/paper/96588a278053dc2e29b5b0d8e2f3fcdf5e5c6a25

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Citations in the corpus

Scalar-tensor theories and modified gravity in the wake of GW170817 (2017, background): “As shown in [33, 34], the quadratic DHOST theories of class I, thus including (8), can be reformulated as Horndeski theories via a disformal transformation of the metric, of the form g̃μν =C(X ,φ)gμν +D(X ,φ)φμ φν , but at the price of introducing a disformal coupling of matter to the metric.”
Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review (2018, methodology): “Type I theories (corresponding to Ia or N-I for quadratic theories, and (3)N-I for cubic ones, according to the terminology used in [13, 16, 17]) are related to Horndeski and Beyond Horndeski theories via disformal transformations (4.”
Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations (2016, methodology): “Note added: the paper [12], which appeared on arXiv during the preparation of this manuscript, also studies the theories introduced in [7] and has some partial overlap with the present work, in particular concerning the disformal transformations in class Ia.”
Gravitational wave decay into dark energy (2018, background): “o decay = f(˚) (4)R+ P(˚;X) + Q(˚;X) ˚: (71) It is interesting to formulate this theory in the context of the more general Degenerate Higher-Order Scalar-Tensor (DHOST) [43] or Extended Scalar-Tensor [44] theories. These theories can be obtained starting from beyond Horndeski and performing an inver”
Effective field theory of dark energy: A review (2019, methodology): “derivatives in the equations of motions, avoid Ostrogradsky instabilities [50] has been exhausted by the Degenerate Higher Order Scalar-Tensor Theories (DHOST) [38, 51, 52, 53, 54, 55].”
Horndeski theory and beyond: a review (2019, background): “is free to add to (110) the Horndeski terms G2(φ,X)−G3(φ,X)✷φ, because these two terms are nothing to do with the degeneracy conditions. Quadratic DHOST theories are classiﬁed into several subclasses [156, 166, 167]. Of particular importance among them is the so called class Ia, which is characteriz”
Degenerate higher order scalar-tensor theories beyond Horndeski up to cubic order (2016, background): “This class was called N-II in [25] and Ib in [26].”
Effective description of higher-order scalar-tensor theories (2017, background): “In fact, they belong to the same subclass of DHOST theories and can be related to each other via disformal transformations [17, 28, 29, 34, 35].”