标题： Barrabes-Israel零壳形式的重新表述 显示英文标题

标题： A reformulation of the Barrabes-Israel null-shell formalism

摘要： 我们考虑一种两个度规在零超曲面上连接的情况。 这种情况经常导致两个度规的并集产生一个包含与零超曲面上的狄拉克δ函数成比例的项的里奇张量。 这种奇异性与零超曲面上的薄物质分布相关，根据Barrabes和Israel的方法，我们试图根据零超曲面的几何性质来确定其应力-能量张量。 虽然我们在这里的处理与他们之前的工作没有太大偏离，但它简化了典型应用该形式主义时涉及的计算操作，并产生了一个具有更易识别现象学的应力-能量张量。 我们对零壳层形式主义的重新表述系统地利用了奇异超曲面的零生成元，这些生成元定义了一个优选的流，物质的流可以与之比较。 此构造通过质量密度、质量电流和各向同性压力，以简单的方式表征了应力-能量张量。 我们的重新表述还涉及一组自由运动的观察者，它们与表面层相交并对它进行测量。 此构造通过将δ函数的参数固定为这些观察者测量的固有时，赋予应力-能量张量操作意义。 显示英文摘要

摘要： We consider a situation in which two metrics are joined at a null hypersurface. It often occurs that the union of the two metrics gives rise to a Ricci tensor that contains a term proportional to a Dirac delta-function supported on the hypersurface. This singularity is associated with a thin distribution of matter on the hypersurface, and following Barrabes and Israel, we seek to determine its stress-energy tensor in terms of the geometric properties of the null hypersurface. While our treatment here does not deviate strongly from their previous work, it offers a simplification of the computational operations involved in a typical application of the formalism, and it gives rise to a stress-energy tensor that possesses a more recognizable phenomenology. Our reformulation of the null-shell formalism makes systematic use of the null generators of the singular hypersurface, which define a preferred flow to which the flow of matter can be compared. This construction provides the stress-energy tensor with a simple characterization in terms of a mass density, a mass current, and an isotropic pressure. Our reformulation also involves a family of freely-moving observers that intersect the surface layer and perform measurements on it. This construction gives operational meaning to the stress-energy tensor by fixing the argument of the delta-function to be proper time as measured by these observers.