Results 1 - 10 of 198
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[en] A hypothesis about collision of two gas-and-dust clouds, which foregoes of origin of the Solar system, explains distribution of an angular momentum in it not quantitatively, but also qualitatively. (author)
[en] Based on the dynamical equivalence between higher order gravity and scalar-tensor gravity the parametrized post-Newtonian (PPN) limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled
[en] There is a distinct possibility that current and future cosmological data can be used to constrain Einstein's theory of gravity on the very largest scales. To be able to do this in a model-independent way, it makes sense to work with a general parameterization of modified gravity. Such an approach would be analogous to the Parameterized Post-Newtonian (PPN) approach which is used on the scale of the Solar System. A few such parameterizations have been proposed and preliminary constraints have been obtained. We show that the majority of such parameterizations are only exactly applicable in the quasistatic regime. On larger scales they fail to encapsulate the full behavior of typical models currently under consideration. We suggest that it may be possible to capture the additions to the 'Parameterized Post-Friedmann' (PPF) formalism by treating them akin to fluid perturbations.
[en] Recently, gravitational microlensing has been investigated in the framework of the weak field limit of fourth order gravity theory. However, solar system data (i.e. planetary periods and light bending) can be used to put strong constraints on the parameters of this class of gravity theories. We find that these parameters must be very close to those corresponding to the Newtonian limit of the theory
[en] Screening mechanisms for a three-form field around a dense source such as the Sun are investigated. Working with the dual vector, we can obtain a thin-shell where field interactions are short range. The field outside the source adopts the configuration of a dipole which is a manifestly distinct behaviour from the one obtained with a scalar field or even a previously proposed vector field model. We identify the region of parameter space where this model satisfies present solar system tests.
[en] We describe a rigorous matched asymptotic expansion, which establishes under very general conditions that local terrestrial and solar-system experiments will measure any variations in 'constants' of Nature occurring on cosmological scales
[en] Several f(R) modified gravity models have been proposed which realize the correct cosmological evolution and satisfy solar system and laboratory tests. Although nonrelativistic stellar configurations can be constructed, we argue that relativistic stars cannot be present in such f(R) theories. This problem appears due to the dynamics of the effective scalar degree of freedom in the strong gravity regime. Our claim thus raises doubts on the viability of f(R) models.
[en] The ubiquitous role of light scalar fields in modified gravity models necessitates the introduction of screening mechanisms whereby gravitation in the solar system can be described by the General Theory of Relativity to an extremely precise level. On larger scales, the laws of gravity can be modified with various phenomelogical consequences. We review the status of the three main mechanisms when a single scalar field modifies gravity. We emphasize the qualitative and quantitative differences between the models subject to the chameleon and the Damour–Polyakov mechanisms on the one hand, and the Vainshtein mechanism on the other hand. (paper)