标题： pp波时空的共形对称性类 显示英文标题

标题： Conformal symmetry classes for pp-wave spacetimes

摘要： 我们确定pp波时空的共形对称类。 这改进了Sippel和Goenner（1986{\it 广义相对论 引力} {\bf 18} 1229）给出的等距分类方案。 结果显示，对于零流体类型$N$的pp波时空，每一个共形Killing向量都是一共形Ricci共线性。 显示在类型$N$的pp波时空中，适当非特殊共形Killing向量的最大数目为三个，并且我们确定了接受此类共形Killing向量的类型$N$的pp波时空的一个特定集合的形式。 我们确定了Sippel和Goenner的每个类型$N$等距类的共形对称性，并提出了新的等距类。 显示英文摘要

摘要： We determine conformal symmetry classes for the pp-wave spacetimes. This refines the isometry classification scheme given by Sippel and Goenner (1986 {\it Gen. Rel. Grav.} {\bf 18} 1229). It is shown that every conformal Killing vector for the null fluid type $N$ pp-wave spacetimes is a conformal Ricci collineation. The maximum number of proper non-special conformal Killing vectors in a type $N$ pp-wave spacetime is shown to be three, and we determine the form of a particular set of type $N$ pp-wave spacetimes admitting such conformal Killing vectors. We determine the conformal symmetries of each type $N$ isometry class of Sippel and Goenner and present new isometry classes.