Title: The Causal Structure of Two-Dimensional Spacetimes Show Chinese title

Title: 二维时空的因果结构

Abstract: We investigate the causal structure of $(1+1)$-dimensional spacetimes. For two sets of field equations we show that at least locally any spacetime is a solution for an appropriate choice of the matter fields. For the theories under consideration we investigate how smoothness of their black hole solutions affects time orientation. We show that if an analog to Hawking's area theorem holds in two spacetime dimensions, it must actually state that the size of a black hole never {\em increases}, contrary to what happens in four dimensions. Finally, we discuss the applicability of the Penrose and Hawking singularity theorems to two spacetime dimensions. Show Chinese abstract

Abstract: 我们研究了$(1+1)$维时空的因果结构。对于两组场方程，我们证明至少在局部范围内，任何时空都可以通过适当选择物质场成为解。对于所考虑的理论，我们探讨了它们的黑洞解的光滑性如何影响时间定向。我们表明，如果霍金面积定理在二维时空中有类似物，那么它实际上必须表述为黑洞的大小永远不会{\em 增加}，这与四维情况不同。最后，我们讨论了彭罗斯和霍金奇点定理在二维时空中的适用性。