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arXiv 0909.1989gr-qc
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爱因斯坦方程的无实体边界数据

Disembodied boundary data for Einstein's equations

Jeffrey Winicour

摘要:

基于Sommerfeld型保约束边界条件,建立了真空Einstein方程的调和方程的强适定初边值问题.这些索末菲条件以前已经提出了一个4维几何形式。在这里,我们将相关的边界数据重新转换为边界固有的三维张量场。这提供了边界数据的几何表示,类似于柯西数据在3度量和外在曲率方面的三维表示。特别是,边界数据的同构导致真空时空的等距几何。适定性的证明对于调和公式及其推广是有效的。Sommerfeld条件可以直接应用于已有的用于模拟二元黑洞的调和码,从而保证了底层解析系统的边界稳定性。边界条件的几何形式也允许它们被正式应用于爱因斯坦方程的任何度量公式,尽管边界问题的适定性不再被保证。我们将讨论在何种程度上这样的正式应用可能会实施约束保持方式的3+1配方,如鲍姆加特夏皮罗柴田中村系统已非常成功的二进制黑洞模拟。

英文摘要:

A strongly well-posed initial boundary value problem based upon constraint-preserving boundary conditions of the Sommerfeld type has been established for the harmonic formulation of the vacuum Einstein's equations. These Sommerfeld conditions have been previously presented in a 4-dimensional geometric form. Here we recast the associated boundary data as 3-dimensional tensor fields intrinsic to the boundary. This provides a geometric presentation of the boundary data analogous to the 3-dimensional presentation of Cauchy data in terms of 3-metric and extrinsic curvature. In particular, diffeomorphisms of the boundary data lead to vacuum spacetimes with isometric geometries. The proof of well-posedness is valid for the harmonic formulation and its generalizations. The Sommerfeld conditions can be directly applied to existing harmonic codes which have been used in simulating binary black holes, thus ensuring boundary stability of the underlying analytic system. The geometric form of the boundary conditions also allows them to be formally applied to any metric formulation of Einstein's equations, although well-posedness of the boundary problem is no longer ensured. We discuss to what extent such a formal application might be implemented in a constraint preserving manner to 3+1 formulations, such as the Baumgarte-Shapiro-Shibata-Nakamura system which has been highly successful in binary black hole simulation.

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