Inherently stable effective field theory for dark energy and modified gravity

Lombriser, Lucas; Dalang, Charles; Kennedy, Joe; Taylor, Andy

doi:10.1088/1475-7516/2019/01/041

Cited by 17 publications

(21 citation statements)

References 156 publications

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“…Fortunately, cosmological observables seem not to be extremely sensitive to short time-scale variations and therefore smooth parameterizations are in general sufficient to describe the theory space in a satisfactory way [325]. A convenient way to fix the EFT functions might be to parameterize directly the stability conditions and derive, subsequently, the evolution of the EFT functions [178,177,179,326]. Alternatively one can use more sophisticated data-driven analysis to reconstruct characteristic functions such as EFT functions, µ, Σ and w DE and then derive specific model properties [101,214].…”

Section: Discussionmentioning

confidence: 99%

“…However it is possible to construct a stable EFT 12 Note that in this investigation the effective Planck mass today was not normalized to M 2 pl . basis which evades ghost and gradient instabilities or accommodates further theoretical priors such as a luminal or sub-luminal scalar propagation speed [177,178,179]. Such basis instead of using the usual EFT functions (or α-basis) employs directly the stability functions α, M 2 , c 2 s with a boundary condition α B0 = const.. An advantage of this basis is that it avoids ΛCDM to be confined to a narrow corner of the stability space.…”

Section: Impact Of Stability Conditionsmentioning

confidence: 99%

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Effective field theory of dark energy: A review

2020

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The discovery of cosmic acceleration has triggered a consistent body of theoretical work aimed at modeling its phenomenology and understanding its fundamental physical nature. In recent years, a powerful formalism that accomplishes both these goals has been developed, the so-called effective field theory of dark energy. It can capture the behavior of a wide class of modified gravity theories and classify them according to the imprints they leave on the smooth background expansion history of the Universe and on the evolution of linear perturbations. The effective field theory of dark energy is based on a Lagrangian description of cosmological perturbations which depends on a number of functions of time, some of which are non-minimal couplings representing genuine deviations from standard gravity. Such a formalism is thus particularly convenient to fit and interpret the wealth of new data that will be provided by future galaxy surveys. Despite its recent appearance, this formalism has already allowed a systematic investigation of what lies beyond the standard gravity landscape and provided a conspicuous amount of theoretical predictions and observational results. In this review, we report on these achievements. Conclusion and outlook 94Appendix A Acronyms and symbols 971. Scalar-tensor theoriesà la Brans-Dicke, hereafter dubbed Generalized

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Section: Discussionmentioning

confidence: 99%

Section: Impact Of Stability Conditionsmentioning

confidence: 99%

Effective field theory of dark energy: A review

2020

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“…There may also be a more physical basis for the correction terms such as that presented in Ref. [44] for linear perturbations, which automatically satisfies the stability constraints at the nonlinear level. We leave such considerations to upcoming studies.…”

Section: Discussionmentioning

confidence: 99%

“…A further set of EFT functions was recently introduced in Ref. [44] with α T = 0 to avoid stability issues associated with the previous EFT bases. Different models such as the cubic Galileon [45,46], quintessence [47] and k-essence [48,49] in general give different functional forms for this set [20].…”

Section: B Reconstruction From Linear Effective Field Theorymentioning

confidence: 99%

“…Finally, it is also of interest to examine what effect these higher-order perturbations have on the physical EFT basis recently introduced in Refs. [31,44]. It consists of parameterizing the EFT formalism in terms of inherently stable basis functions: The effective Planck mass squared M 2 , the sound-speed squared c 2 s , the kinetic energy of the scalar field α and the background expansion H(t), along with α B0 .…”

Section: Higher-order Reconstructionmentioning

confidence: 99%

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Screening and degenerate kinetic self-acceleration from the nonlinear freedom of reconstructed Horndeski theories

2019

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We have previously presented a reconstruction of Horndeski scalar-tensor theories from linear cosmological observables. It includes free nonlinear terms which can be added onto the reconstructed covariant theory without affecting the background and linear dynamics. After discussing the uniqueness of these correction terms, we apply this nonlinear freedom to a range of different applications. First we demonstrate how the correction terms can be configured to endow the reconstructed models with screening mechanisms such as the chameleon, k-mouflage and Vainshtein effects. A further implication is the existence of classes of Horndeski models that are degenerate with standard cosmology to an arbitrary level in the cosmological perturbations. Particularly interesting examples are kinetically self-accelerating models that mimic the dynamics of the cosmological constant to an arbitrary degree in perturbations. Finally, we develop the reconstruction method further to the level of higher-order effective field theory, which under the restriction to a luminal propagation speed of gravitational waves introduces two new free functions per order. These functions determine the corresponding correction terms in the linearly reconstructed action at the same order. Our results enable the connection of linear cosmological constraints on generalised modifications of gravity and dark energy with the nonlinear regime and astrophysical probes for a more global interpretation of the wealth of forthcoming cosmological survey data.

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Testing general relativity in cosmology

2018

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We review recent developments and results in testing general relativity (GR) at cosmological scales. The subject has witnessed rapid growth during the last two decades with the aim of addressing the question of cosmic acceleration and the dark energy associated with it. However, with the advent of precision cosmology, it has also become a well-motivated endeavor by itself to test gravitational physics at cosmic scales. We overview cosmological probes of gravity, formalisms and parameterizations for testing deviations from GR at cosmological scales, selected modified gravity (MG) theories, gravitational screening mechanisms, and computer codes developed for these tests. We then provide summaries of recent cosmological constraints on MG parameters and selected MG models. We supplement these cosmological constraints with a summary of implications from the recent binary neutron star merger event. Next, we summarize some results on MG parameter forecasts with and without astrophysical systematics that will dominate the uncertainties. The review aims at providing an overall picture of the subject and an entry point to students and researchers interested in joining the field. It can also serve as a quick reference to recent results and constraints on testing gravity at cosmological scales.

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Inherently stable effective field theory for dark energy and modified gravity

Abstract: The growing wealth of cosmological observations places succeedingly more strin-

Cited by 17 publications

References 156 publications

Effective field theory of dark energy: A review

Effective field theory of dark energy: A review

Screening and degenerate kinetic self-acceleration from the nonlinear freedom of reconstructed Horndeski theories

Testing general relativity in cosmology

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