论文标题
修饰重力的因果层次结构
Causal hierarchy in modified gravity
论文作者
论文摘要
我们研究了各种重力理论的因果关系。总体而言，标准因果层次结构（其关键要素是年代学，因果关系，强烈的因果关系，稳定的因果关系和全球性超波斯性）。在经过修改的重力理论中，通常存在相当大的额外结构（例如：多个指标，以太字段，修改后的分散关系，类似Horava的重力，抛物线式传播等），需要重新评估和重新评估通常的因果关系。我们将表明，在这个扩展的框架中，确实可以建立适当的因果层次结构，并讨论“静光”传播和因果关系之间相互作用的含义。关键的区别特征是信号速度是有限的还是无限的。在存在无限信号速度的情况下，即使维护因果关系的最小概念也要求以太场既独特又是超声正交的，这使我们引入了全球抛物性的概念。
We investigate the causal hierarchy in various modified theories of gravity. In general relativity the standard causal hierarchy, (key elements of which are chronology, causality, strong causality, stable causality, and global hyperbolicity), is well-established. In modified theories of gravity there is typically considerable extra structure, (such as: multiple metrics, aether fields, modified dispersion relations, Horava-like gravity, parabolic propagation, etcetera), requiring a reassessment and rephrasing of the usual causal hierarchy. We shall show that in this extended framework suitable causal hierarchies can indeed be established, and discuss the implications for the interplay between "superluminal" propagation and causality. The key distinguishing feature is whether the signal velocity is finite or infinite. Preserving even minimal notions of causality in the presence of infinite signal velocity requires the aether field to be both unique and hypersurface orthogonal, leading us to introduce the notion of global parabolicity.
