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arXiv 1009.5231gr-qc
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类哥德尔时空的光锥

The lightcone of Gödel-like spacetimes

G. Dautcourt

摘要:

对哥德尔宇宙光锥的研究被扩展到所谓的类哥德尔时空。这个高度对称的四维洛伦兹空间族是由$ds^2=-(dt+H(x)dy)^2+D^2(x)dy^2+dx^2+dz^2$形式的度规定义的,加上时空均匀性的要求,并且包括哥德尔度规。具有惊人透镜性质的锥发生器的准周期性重聚焦,是整个哥德尔家族的一个特征,由厄兹瓦特和许金发现,用于平面引力波的光锥,也在哥德尔宇宙中发现。我们讨论焦散线的几何性质,并表明:(a)焦面是由非测地零曲线生成的二维零曲面和(b)锥的固有微分不变量在焦散子集处达到有限值。

英文摘要:

A study of the lightcone of the Gödel universe is extended to the so-called Gödel-like spacetimes. This family of highly symmetric 4-D Lorentzian spaces is defined by metrics of the form $ds^2=-(dt+H(x)dy)^2+D^2(x)dy^2+dx^2+dz^2$, together with the requirement of spacetime homogeneity, and includes the Gödel metric. The quasi-periodic refocussing of cone generators with startling lens properties, discovered by Ozsváth and Schücking for the lightcone of a plane gravitational wave and also found in the Gödel universe, is a feature of the whole Gödel family. We discuss geometrical properties of caustics and show that (a) the focal surfaces are two-dimensional null surfaces generated by non-geodesic null curves and (b) intrinsic differential invariants of the cone attain finite values at caustic subsets.

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