Disformally self-tuning gravity

Emond, William T.; Saffin, Paul M.

doi:10.1007/jhep03(2016)161

Cited by 6 publications

(7 citation statements)

References 68 publications

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“…The X-dependent disformal transformations have also been studied recently in several papers (see e.g. [13][14][15][16][17], and [18] for scalar tensor theories that explicitly break spacetime covariance [19].) In this work, we present the general disformal transformation of all quadratic DHOST theories identified in [7].…”

Section: Introductionmentioning

confidence: 93%

Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations

2016

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International audienceWe 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, whose degeneracy, in general, ensures the absence of Ostrogradsky’s instability, include the quartic Horndeski Lagrangian and its quartic extension beyond Horndeski, as well as other Lagrangians. We study how all these theories transform under general disformal transformations and find that they can be separated into three main classes that are stable under these transformations. This leads to a complete classification modulo disformal transformations. Finally, we show that these higher order theories include mimetic gravity and some particular khronometric theories. They also contain theories that do not correspond, to our knowledge, to already studied theories, even up to disformal transformations

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Section: Introductionmentioning

confidence: 93%

Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations

2016

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“…Cosmic self-tuning mechanisms have recently been proposed (see, e.g., [5][6][7][8][9][10][11][12][13][14][15]), which dynamically remove a large vacuum energy and potentially give rise to the current cosmic acceleration. Weinberg proved a no-go theorem on various mechanisms designed to remove vacuum energy, which ended earlier attempts on this direction (see [16] and references therein).…”

Section: Introductionmentioning

confidence: 99%

Well-tempered cosmology

Emond

Saffin

et al. 2019

J. Cosmol. Astropart. Phys.

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We examine an approach to cosmology, known as Well-Tempering, that allows for a de Sitter phase whose expansion is independent of the cosmological constant. Starting from a generic scalar-tensor theory compatible with the recent gravitational wave observation, we impose the Well-Tempering conditions and derive a system that is capable of tuning away the cosmological constant within a sub-class of Horndeski theory, where the scalar has a canonical kinetic term and a general potential. This scenario improves upon the Fab-Four approach by allowing a standard fluid-cosmology before entering the de Sitter phase, and we present an explicit example of our general solution.

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“…Its generalisation, known as Beyond Horndeski or GLPV theories, contain higher order derivative terms but are nonetheless healthy in the sense that they avoid instabilities [32]. Analogously, it has been shown [33] that the Lagrangian structure of GLPV models is preserved under disformal transformations of the form C ≡ C(φ) and D ≡ D(φ, X), [34][35][36]. However, if C ≡ C(φ, X), terms that do not belong to the GLPV setting may arise, which are the cause of Ostrogatski instabilities [37].…”

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confidence: 99%

Disformally coupled quintessence

Teixeira

Nunes

2020

Phys. Rev. D

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In this work we consider a cosmological model in which dark energy is portrayed by a canonical scalar field which is allowed to couple to the other species by means of a disformal transformation of the metric. We revisit the current literature by assuming that the disformal function in the metric transformation can depend both on the scalar field itself and on its derivatives, encapsulating a wide variety of scalar-tensor theories. This generalisation also leads to new and richer phenomenology, explaining some of the features found in previously studied models. We present the background equations and perform a detailed dynamical analysis, from where new disformal fixed points emerge, that translate into novel cosmological features. These include early scaling regimes between the coupled species and broader stability parameter regions. However, viable cosmological models seem to have suppressed disformal late-time contributions. I. IntroductionSince 1998 that we have been witnessing growing observational confirmation of the present accelerated expansion of the Universe [1][2][3][4]. This phenomenon can be attributed to an exotic fluid, the so-called Dark Energy (DE), which must amount to about 70% of the total content of the Universe, and whose effective negative pressure can successfully explain the observations (see [5][6][7] for recent reviews). Presently, the ΛCDM model is the most well-accepted cosmological model, consisting of a cosmological constant dark energy source, Λ, plus a dark matter component, needed in order to make formation of structure possible in the Universe [8]. However, this paradigm faces some theoretical inconsistencies [9], motivating extensions of the concept of dark energy to a scalar field, with General Relativity as the underlying gravitational theory [10][11][12]. These scalar field based models, albeit simple, can give rise to very complex and rich phenomenologies, while making predictions that are testable according to observational constraints [4]. In the plainest scenarios, DE is portrayed as a canonical scalar field, the quintessence field, which does not interact with the other components in the Universe [13,14]. However, there is no fundamental reason to assume such a constraint and, in the simplest extension, the scalar field is allowed to couple non-minimally to the matter sector [15][16][17][18][19][20][21][22][23].One straightforward procedure for introducing a non-trivial coupling between the scalar field and matter is to consider that matter particles propagate in geodesics of a transformed metric,ḡ µν , related to the gravitational metric, g µν , by means of a field-dependent transformation. When this transformation corresponds to a rescaling of the metric we speak of conformal transformations, which affect the length of time-like and space-like intervals and the norm of time-like and space-like vectors while leaving the light cones unchanged:where C is the conformal factor. Conformal transformations are known to preserve the structure of Scalar-Tensor theories of the B...

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Disformally self-tuning gravity

Cited by 6 publications

References 68 publications

Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations

Degenerate higher order scalar-tensor theories beyond Horndeski and disformal transformations

Well-tempered cosmology

Disformally coupled quintessence

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