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Gravitation

About: Gravitation is a research topic. Over the lifetime, 29306 publications have been published within this topic receiving 821510 citations.


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TL;DR: In this paper, it is shown that models with negative powers of the scalar curvature, like the ones used to explain the present accelerated expansion, as well as their generalization which include positive powers, can give the correct Newtonian limit, as long as the coefficients of these powers are reasonably small.
Abstract: The present paper reconsiders the Newtonian limit of models of modified gravity including higher order terms in the scalar curvature in the gravitational action. This was studied using the Palatini variational principle in Meng and Wang (Gen. Rel. Grav. 36, 1947 (2004)) and Dominguez and Barraco (Phys. Rev. D 70, 043505 (2004)) with contradicting results. Here a different approach is used, and problems in the previous attempts are pointed out. It is shown that models with negative powers of the scalar curvature, like the ones used to explain the present accelerated expansion, as well as their generalization which include positive powers, can give the correct Newtonian limit, as long as the coefficients of these powers are reasonably small. Some consequences of the performed analysis seem to raise doubts for the way the Newtonian limit was derived in the purely metric approach of fourth order gravity [Dick in Gen. Rel. Grav. 36, 217 (2004)]. Finally, we comment on a recent paper [Olmo in Phys. Rev. D 72, 083505 (2005)] in which the problem of the Newtonian limit of both the purely metric and the Palatini formalism is discussed, using the equivalent Brans–Dicke theory, and with which our results partly disagree.

156 citations

Journal ArticleDOI
Roman Konoplya1
TL;DR: In this paper, the same authors considered the deformed Horava-Lifshitz gravity with Minkowski vacuum and showed that the bending angle is smaller in the considered Horava−Lititz gravity than in GR, while the quasinormal modes of black holes are longer lived and have larger real oscillation frequency in the Horava −Litzitz gravity.

156 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that the brane tension does not imply a self-tuning of the effective 4D cosmological constant to zero; perturbations of the tension in a static solution lead to deSitter or anti-deSitter braneworlds.
Abstract: It has been suggested that codimension-two braneworlds might naturally explain the vanishing of the 4D effective cosmological constant, due to the automatic relation between the deficit angle and the brane tension. To investigate whether this cancellation happens dynamically, and within the context of a realistic cosmology, we study a codimension-two braneworld with spherical extra dimensions compactified by magnetic flux. Assuming Einstein gravity, we show that when the brane contains matter with an arbitrary equation of state, the 4D metric components are not regular at the brane, unless the brane has nonzero thickness. We construct explicit 6D solutions with thick branes, treating the brane matter as a perturbation, and find that the universe expands consistently with standard Friedmann-Robertson-Walker (FRW) cosmology. The relation between the brane tension and the bulk deficit angle becomes $\ensuremath{\Delta}=2\ensuremath{\pi}{G}_{6}(\ensuremath{\rho}\ensuremath{-}3p)$ for a general equation of state. However, this relation does not imply a self-tuning of the effective 4D cosmological constant to zero; perturbations of the brane tension in a static solution lead to deSitter or anti-deSitter braneworlds. Our results thus confirm other recent work showing that codimension-two braneworlds in nonsupersymmetric Einstein gravity do not lead to a dynamical relaxation of the cosmological constant, but they leave open the possibility that supersymmetric versions can be compatible with self-tuning.

156 citations

Journal ArticleDOI
TL;DR: In this article, exact multiparticle scattering amplitudes are computed in terms of expectation values of Wilson lines, and the two-particle amplitude reduces to an earlier result of 't Hooft.

155 citations

Journal ArticleDOI
TL;DR: In this paper, the authors focus on the emergence of limiting configurations of the Reissner-Nordstrom field that have vanishing effective mass everywhere within the sphere and show that these configurations prevent the existence of naked singularities, and demand that the effective gravitational mass be everywhere non-negative.
Abstract: The energy conditions of general relativity are satisfied by all experimentally detected fields. We discuss their interpretation and application to charged spheres. It is found that they prevent the existence of naked singularities, and demand that the effective gravitational mass be everywhere non-negative. We focus on the emergence of limiting configurations-sources of the Reissner-Nordstrom field that have vanishing effective mass everywhere within the sphere. These configurations have a number of interesting features. Among them we find that, near the center, the limiting form of the equation of state isρ+3p=0. Notably this is the only equation of state consistent with the existence of zero-point electromagnetic field, and it has been considered in different contexts, in discussions of cosmic strings and in derivations of (3+1) properties of matter from (4+1) geometry. The consistency of these configurations with the Einstein-Maxwell equations is shown by means of explicit examples. These configurations can be interpreted as due to selfinteracting gravitational effects of the zero-point electromagnetic field.

155 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023745
20221,538
20211,353
20201,587
20191,566
20181,592