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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Mimetic Gravity: A Review of Recent Developments and Applications to Cosmology and Astrophysics
TL;DR: Mimetic gravity is a Weyl-symmetric extension of General Relativity, related to the latter by a singular disformal transformation, wherein the appearance of a dust-like perfect fluid can mimic cold dark matter at a cosmological level as discussed by the authors.
Journal ArticleDOI
The null energy condition and its violation
TL;DR: A brief review of scalar field theories with second-derivative Lagrangians yielding second-order field equations is given in this article, where the use of these theories in constructing cosmological scenarios and in the context of a laboratory-created universe is illustrated with examples.
Journal ArticleDOI
Anisotropic stress as a signature of nonstandard propagation of gravitational waves.
TL;DR: It is shown that in cosmological solutions of very general classes of models extending gravity-all scalar-tensor theories, Einstein-aether models, and bimetric massive gravity-a direct correspondence exists between perfect fluids apparently carrying anisotropic stress and a modification in the propagation of gravitational waves.
Journal ArticleDOI
Bouncing Galileon cosmologies
TL;DR: In this paper, nonsingular, homogeneous and isotropic bouncing solutions of the conformal Galileon model were presented, and it was shown that such solutions necessarily begin with a radiation-dominated contracting phase.
Journal ArticleDOI
Gravitational Rainbows: LIGO and Dark Energy at its Cutoff
TL;DR: It is shown how the operators that naturally lie at the cutoff scale can affect the speed of propagation of gravitational waves and bring it back to unity at LIGO scales in a simple model with a known partial UV completion.
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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