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Four-force
About: Four-force is a research topic. Over the lifetime, 3459 publications have been published within this topic receiving 87308 citations.
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01 Jan 2020
118 citations
TL;DR: In this paper, a spin foam formulation of Lorentzian quantum general relativity is presented, which is based on a simple generalization of a Euclidean model defined in terms of a field theory over a group.
Abstract: We present a spin foam formulation of Lorentzian quantum general relativity. The theory is based on a simple generalization of a Euclidean model defined in terms of a field theory over a group. Its vertex amplitude turns out to be the one recently introduced by Barrett and Crane. As in the case of its Euclidean relatives, the model fully implements the desired sum over 2-complexes which encodes the local degrees of freedom of the theory.
117 citations
TL;DR: In this article, it was shown that the original variational principle can be generalized to general motions of the perfect fluid and the form of the basic Lagrangian density is unchanged by these generalizations.
Abstract: A previously discussed variational principle for a perfect fluid in general relativity was restricted to irrotational, isentropic motions of the fluid. It is proven that these restrictions can be dropped, and the original variational principle can be generalized to general motions of the perfect fluid. The form of the basic Lagrangian density is unchanged by these generalizations. An Eulerian fluid description is used throughout. As a by‐product of our variational principle, the 4‐velocity is required to have the generalized Clebsch form.
116 citations
TL;DR: The boundary terms in the action for Regge's formulation of general relativity on a simplicial net were derived and compared with the boundary terms for general relativity in continuum general relativity.
Abstract: The boundary terms in the action for Regge's formulation of general relativity on a simplicial net are derived and compared with the boundary terms in continuum general relativity.
116 citations