Journal ArticleDOI
Second-order scalar-tensor field equations in a four-dimensional space
TLDR
In this article, the second-order Euler-Lagrange tensors are derived from a Lagrangian which is at most of second order in the derivatives of the field functions.Abstract:
Lagrange scalar densities which are concomitants of a pseudo-Riemannian metric-tensor, a scalar field and their derivatives of arbitrary order are considered. The most general second-order Euler-Lagrange tensors derivable from such a Lagrangian in a four-dimensional space are constructed, and it is shown that these Euler-Lagrange tensors may be obtained from a Lagrangian which is at most of second order in the derivatives of the field functions.read more
Citations
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Dark Energy and Modified Gravity in the Effective Field Theory of Large-Scale Structure
TL;DR: In this article, an approach to compute observables beyond the linear regime of dark matter perturbations for general dark energy and modified gravity models is presented. But the approach is restricted to the case of Horndeski theories and assumes the quasi-static approximation.
Journal ArticleDOI
Effective Field Theory of Dark Energy: a Dynamical Analysis
TL;DR: In this paper, the feasibility of the EFT of dark energy and modified gravity models is investigated by means of a thorough dynamical analysis, where the system is underdetermined, and one can always find a set of functions reproducing any expansion history.
Journal ArticleDOI
On the possibility of blue tensor spectrum within single field inflation
Yi-Fu Cai,Yi-Fu Cai,Jinn Ouk Gong,Jinn Ouk Gong,Shi Pi,Emmanuel N. Saridakis,Emmanuel N. Saridakis,Shang-Yu Wu +7 more
TL;DR: In this paper, the authors present a series of theoretical constraints on the potentially viable inflation models that might yield a blue spectrum for primordial tensor perturbations, and show that, while there exists such possibility, the corresponding phase space is strongly bounded.
Journal ArticleDOI
Cosmology in bimetric theory with an effective composite coupling to matter
A. Emir Gümrükçüoğlu,Lavinia Heisenberg,Shinji Mukohyama,Shinji Mukohyama,Norihiro Tanahashi +4 more
TL;DR: In this paper, the cosmology of bimetric theory with a composite matter coupling was studied and conditions on the absence of ghost and gradient instabilities were derived for tensor and vector perturbations.
Journal ArticleDOI
Exorcising the Ostrogradsky ghost in coupled systems
Remko Klein,Diederik Roest +1 more
TL;DR: In this article, the Ostrogradsky theorem implies that higher-derivative terms of a single mechanical variable are either trivial or lead to additional, ghost-like degrees of freedom.
References
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Journal ArticleDOI
Mach's principle and a relativistic theory of gravitation
Carl H. Brans,R. H. Dicke +1 more
TL;DR: In this paper, the role of Mach's principle in physics is discussed in relation to the equivalence principle and the difficulties encountered in attempting to incorporate Mach's principles into general relativity are discussed.
Journal ArticleDOI
The Einstein Tensor and Its Generalizations
TL;DR: In this paper, the number of independent tensors of this type depends crucially on the dimension of the space, and, in the four dimensional case, the only tensors with these properties are the metric and the Einstein tensors.
Journal ArticleDOI
Comments on the scalar-tensor theory
TL;DR: In this article, the ponderomotive laws of a scalar-tensor theory are constructed free of approximations in the form of integral laws, and the integrals are extended over two-and three-dimensional domains that lie entirely in empty space but surround the regions containing matter.
Journal ArticleDOI
The uniqueness of the einstein field equations in a four-dimensional space.
TL;DR: In this article, the Euler-Lagrange equations corresponding to a Lagrange density which is a function of g ≥ 2 and its first two derivatives are investigated and necessary and sufficient conditions for these equations to be of second order are obtained and it is shown that in a four-dimensional space the Einstein field equations (with cosmological term) are the only permissible second order Euler Lagrange equations.
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