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arXiv 1306.2375gr-qc
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(2+2)形式中的时间问题和哈密尔顿约化

Problem of time and Hamiltonian reduction in the (2+2) formalism

Jong Hyuk Yoon

摘要:

我们将哈密顿约化过程应用于一般四维时空的(2+2)形式,找到了物理哈密顿量仅以真自由度表示的特殊时空坐标,即零超曲面截面上的共形二度规及其共轭动量.物理时间是零超曲面截面的面积元,物理径向坐标由给定的常物理时间类空超曲面上的{ \it等势}曲面定义.物理哈密顿量是{ \it约束自由},并且在特权坐标中明显是{ \it正定}。我们给出了哈密顿方程的完整集合,并发现它们与特权坐标下的爱因斯坦方程相吻合。这表明,我们的哈密顿约化是自洽的,并尊重一般的协方差。本文将半超空间的ADM Hamilton约化推广到四维无等距时空。

英文摘要:

We apply the Hamiltonian reduction procedure to general spacetimes of 4-dimensions in the (2+2) formalism and find privileged spacetime coordinates in which the physical Hamiltonian is expressed in true degrees of freedom only, namely, the conformal two-metric on the cross section of null hypersurfaces and its conjugate momentum. The physical time is the area element of the cross section of null hypersurface, and the physical radial coordinate is defined by {\it equipotential} surfaces on a given spacelike hypersurface of constant physical time. The physical Hamiltonian is {\it constraint-free} and manifestly {\it positive-definite} in the privileged coordinates. We present the complete set of the Hamilton's equations, and find that they coincide with the Einstein's equations written in the privileged coordinates. This shows that our Hamiltonian reduction is self-consistent and respects the general covariance. This work is a generalization of ADM Hamiltonian reduction of midi-superspace to 4-dimensional spacetimes with no isometries.

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