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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 article, the sonic analog of a gravitational black hole in dilute-gas Bose-Einstein condensates is investigated, and it is shown that there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit behaviors completely analogous to that of gravitational black holes.
Abstract: The sonic analog of a gravitational black hole in dilute-gas Bose-Einstein condensates is investigated It is shown that there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit behaviors completely analogous to that of gravitational black holes The dynamical instabilities involve the creation of quasiparticle pairs in positive and negative energy states We illustrate these features in two qualitatively different one-dimensional models, namely, a long, thin condensate with an outcoupler laser beam providing an ``atom sink,'' and a tight ring-shaped condensate We also simulate the creation of a stable sonic black hole by solving the Gross-Pitaevskii equation numerically for a condensate subject to a trapping potential which is adiabatically deformed A sonic black hole could, in this way, be created experimentally with state-of-the-art or planned technology
240 citations
TL;DR: In this article, it was shown that the Ricci scalar-tensor theory is equivalent to a scalar field kinetic energy term in which the scalar energy term is absent from the action.
Abstract: It has been suggested that the Universe's recent acceleration is due to a contribution to the gravitational action proportional to the reciprocal of the Ricci scalar. Although the original version of this theory disagrees with solar system observations, a modified Palatini version, in which the metric and connection are treated as independent variables, has been suggested as a viable model of the cosmic acceleration. We show that this theory is equivalent to a scalar-tensor theory in which the scalar field kinetic energy term is absent from the action. Integrating out the scalar field gives rise to additional interactions among the matter fields of the standard model of particle physics at an energy scale of order ${10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{e}\mathrm{V}$ (the geometric mean of the Hubble and the Planck scales), and so the theory is excluded by, for example, electron-electron scattering experiments.
240 citations
TL;DR: In this paper, the first, simulation calibrated, cluster abundance constraints on a modified gravity model, specifically the modified action f(R) model, were presented and compared with geometric and high redshift data from the cosmic microwave background, supernovae, H0 and baryon acoustic oscillations, improving previous constraints by nearly 4 orders of magnitude in the field amplitude.
Abstract: Modified gravitational forces in models that seek to explain cosmic acceleration without dark energy typically predict deviations in the abundance of massive dark matter halos. We conduct the first, simulation calibrated, cluster abundance constraints on a modified gravity model, specifically the modified action f(R) model. The local cluster abundance, when combined with geometric and high redshift data from the cosmic microwave background, supernovae, H0 and baryon acoustic oscillations, improve previous constraints by nearly 4 orders of magnitude in the field amplitude. These limits correspond to a 2 order of magnitude improvement in the bounds on the range of the force modification from the several Gpc scale to the tens of Mpc scale.
239 citations
01 Oct 2002
TL;DR: Visser et al. as mentioned in this paper presented a survey of the evolution of general Relativity and the physics of Black Hole Horizons in the context of superfluid physics, including the role of Sonic Metric in Relativistic Superfluid.
Abstract: Contents: Introduction and Survey (M Visser) Acoustic Black Holes in Dilute Bose-Einstein Condensates (L Garay) Slow Light (U Leonhardt) Black Hole and Baby Universe in a Thin Film of 3He-A (T Jacobson & T Koike) Measurability of Dumb Hole Radiation? (W Unruh) Effective Gravity and Quantum Vacuum in Superfluids (G Volovik) Emergent Relativity and the Physics of Black Hole Horizons (G Chapline et al.) Quasi-Gravity in Branes (B Carter) Towards a Collective Treatment of Quantum Gravitational Interactions (R Parentani) Role of Sonic Metric in Relativistic Superfluid (B Carter) Effective Geometry in Nonlinear Field Theory (Electrodynamics and Gravity) (M Novello) Non-Inertial Quantum Mechanical Fluctuations (H Rosu) Phonons and Forces: Momentum versus Pseudomomentum (M Stone) Coda (M Visser) Appendix: Elements of General Relativity (M Visser).
239 citations
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TL;DR: In this article, the authors relate the physics of charged, asymptotically anti-de Sitter spacetimes to the phenomenology of low temperature critical phases of condensed matter.
Abstract: The holographic correspondence creates an interface between classical gravitational physics and the dynamics of strongly interacting quantum field theories. This chapter will relate the physics of charged, asymptotically Anti-de Sitter spacetimes to the phenomenology of low temperature critical phases of condensed matter. Common essential features will characterise both the gravitational and field theoretic systems. Firstly, an emergent scaling symmetry at the lowest energy scales appears as an emergent isometry in the interior, `near horizon' regime of the spacetime. Secondly, the field theoretic distinction between fractionalized and mesonic phases appears as the presence or absence of a charge-carrying horizon in the spacetime. A perspective grounded in these two characteristics allows a unified presentation of `holographic superconductors', `electron stars' and `charged dilatonic spacetimes'.
238 citations