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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, the problem of determining the changes in the gravitational field caused by particle creation is investigated in the context of the semiclassical approximation, where the spacetime geometry is treated classically and an effective stress energy is assigned to the created particles which acts as a source of the gravitational force.
Abstract: The problem of determining the changes in the gravitational field caused by particle creation is investigated in the context of the semiclassical approximation, where the gravitational field (i.e., spacetime geometry) is treated classically and an effective stress energy is assigned to the created particles which acts as a source of the gravitational field. An axiomatic approach is taken. We list five conditions which the renormalized stress-energy operatorTμv should satisfy in order to give a reasonable semiclassical theory. It is proven that these conditions uniquely determineTμv, i.e. there is at most one renormalized stress-energy operator which satisfies all the conditions. We investigate existence by examining an explicit “point-splitting” type prescription for renormalizingTμv. Modulo some standard assumptions which are made in defining the prescription forTμv, it is shown that this prescription satisfies at least four of the five axioms.

271 citations

Journal ArticleDOI
TL;DR: Agile Boltztran as discussed by the authors solves the Boltzmann transport equation for the angular and spectral neutrino distribution functions in self-consistent simulations of stellar core collapse and postbounce evolution.
Abstract: We present an implicit finite difference representation for general relativistic radiation hydrodynamics in spherical symmetry. Our code, Agile-Boltztran, solves the Boltzmann transport equation for the angular and spectral neutrino distribution functions in self-consistent simulations of stellar core collapse and postbounce evolution. It implements a dynamically adaptive grid in comoving coordinates. Most macroscopically interesting physical quantities are defined by expectation values of the distribution function. We optimize the finite differencing of the microscopic transport equation for a consistent evolution of important expectation values. We test our code in simulations launched from progenitor stars with 13 solar masses and 40 solar masses. ~0.5 s after core collapse and bounce, the protoneutron star in the latter case reaches its maximum mass and collapses further to form a black hole. When the hydrostatic gravitational contraction sets in, we find a transient increase in electron flavor neutrino luminosities due to a change in the accretion rate. The muon- and tauon-neutrino luminosities and rms energies, however, continue to rise because previously shock-heated material with a non-degenerate electron gas starts to replace the cool degenerate material at their production site. We demonstrate this by supplementing the concept of neutrinospheres with a more detailed statistical description of the origin of escaping neutrinos. We compare the evolution of the 13 solar mass progenitor star to simulations with the MGFLD approximation, based on a recently developed flux limiter. We find similar results in the postbounce phase and validate this MGFLD approach for the spherically symmetric case with standard input physics.

270 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that in theories of gravity where the cosmological constant is considered a thermodynamic variable, it is natural to use black holes as heat engines.
Abstract: It is shown that in theories of gravity where the cosmological constant is considered a thermodynamic variable, it is natural to use black holes as heat engines. Two examples are presented in detail using AdS charged black holes as the working substance. We notice that for static black holes, the maximally efficient traditional Carnot engine is also a Stirling engine. The case of negative cosmological constant supplies a natural realization of these engines in terms of the field theory description of the fluids to which they are holographically dual. We first propose a precise picture of how the traditional thermodynamic dictionary of holography is extended when the cosmological constant is dynamical and then conjecture that the engine cycles can be performed by using renormalization group flow. We speculate about the existence of a natural dual field theory counterpart to the gravitational thermodynamic volume.

270 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the quantum back-reaction on an initially inflating, homogeneous and isotropic universe whose topology is T 3 x ℛ and showed that two-loop processes act to slow the rate of expansion by an amount which becomes nonperturbatively large at late times.

270 citations

Journal ArticleDOI
TL;DR: In this paper, a simple, systematic and direct approach to decoupling gravitational sources in general relativity is presented, and a robust and simple way to generate anisotropic solutions for self-gravitating systems from perfect fluid solutions is presented.
Abstract: We show a simple, systematic and direct approach to decoupling gravitational sources in general relativity. As a direct application, a robust and simple way to generate anisotropic solutions for self-gravitating systems from perfect fluid solutions is presented.

268 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