标题： 关于允许无剪切、无旋转、测地类时族的时空 显示英文标题

标题： On Spacetimes Admitting Shear-free, Irrotational, Geodesic Timelike Congruences

摘要： 对具有无剪切、无旋且测地类时共轭的广义相对论时空进行全面分析。 对于一般能量动量张量的模型，列出了控制方程。 建立了使此类时空度规呈现简化形式的坐标系。 研究了“零各向异性应力”、“零热通量矢量”和“两组分流体”的一般子情况。 特别是讨论了完美流体弗里德曼-罗伯逊-沃克模型和空间齐性模型。 考虑了具有多种物理相关能量动量张量的模型。 检查了各向异性流体模型和具有热传导的粘性流体模型。 此外，还研究了具有完美流体加磁场或纯辐射的模型，以及具有两个非共线完美流体（满足各种物理条件）的模型。 特别是讨论了相对于无剪切、无旋且无加速度的类时共轭具有倾斜的（单个）完美流体模型。 显示英文摘要

摘要： A comprehensive analysis of general relativistic spacetimes which admit a shear-free, irrotational and geodesic timelike congruence is presented. The equations governing the models for a general energy-momentum tensor are written down. Coordinates in which the metric of such spacetimes takes on a simplified form are established. The general subcases of `zero anisotropic stress', `zero heat flux vector' and `two component fluids' are investigated. In particular, perfect fluid Friedmann-Robertson-Walker models and spatially homogeneous models are discussed. Models with a variety of physically relevant energy-momentum tensors are considered. Anisotropic fluid models and viscous fluid models with heat conduction are examined. Also, models with a perfect fluid plus a magnetic field or with pure radiation, and models with two non-collinear perfect fluids (satisfying a variety of physical conditions) are investigated. In particular, models with a (single) perfect fluid which is tilting with respect to the shear-free, vorticity-free and acceleration-free timelike congruence are discussed.