Causal structures in Gauss-Bonnet gravity
Causal structures in Gauss-Bonnet gravity
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DOI：
10.1103/physrevd.90.044037
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发表时间：
2014-06
影响因子：
5
通讯作者：
K. Izumi
中科院分区：
文献类型：
--
作者：
K. Izumi
我们分析了Gauss-Bonnet引力的因果结构。众所周知，由于其非正则动力学项，Gauss-Bonnet引力具有潜在的引力子超光速传播。在一个有超光速模式的理论中，基于零曲线的因果关系分析是没有意义的，因此，我们需要以不同的方式分析它们。本文用特征线法分析了高斯-引力帽引力中的因果结构。我们得到的结果是，在杀伤视界上，引力子可以沿着与杀伤视界相切的零方向传播。因此，杀戮视界可以是一个因果边缘，就像广义相对论的情况一样，即杀戮视界是因果意义上的“事件视界”。我们还分析了具有$(D-2)$维极大对称性的非定常解的因果结构，包括球对称空间和平坦空间。如果满足几何零能量条件：对于任何零矢量$N^A$，引力子的径向速度必须小于或等于光的速度。然而，如果违反几何零能量条件，引力子的传播速度可能会快于光速。因此，在几何零能量条件不成立的蒸发黑洞上，经典引力子可以从零曲线定义的“黑洞”中逃逸。也就是说，因果结构变得非同寻常。这可能是解决蒸发黑洞信息损失悖论的可能方法之一。
We analyze causal structures in Gauss-Bonnet gravity. It is known that Gauss-Bonnet gravity potentially has superluminal propagation of gravitons due to its noncanonical kinetic terms. In a theory with superluminal modes, an analysis of causality based on null curves makes no sense, and thus, we need to analyze them in a different way. In this paper, using the method of the characteristics, we analyze the causal structure in Gauss-Bonnet gravity. We have the result that, on a Killing horizon, gravitons can propagate in the null direction tangent to the Killing horizon. Therefore, a Killing horizon can be a causal edge as in the case of general relativity, i.e. a Killing horizon is the "event horizon" in the sense of causality. We also analyze causal structures on nonstationary solutions with $(D-2)$-dimensional maximal symmetry, including spherically symmetric and flat spaces. If the geometrical null energy condition, $R_{AB}N^AN^B \ge 0$ for any null vector $N^A$, is satisfied, the radial velocity of gravitons must be less than or equal to that of light. However, if the geometrical null energy condition is violated, gravitons can propagate faster than light. Hence, on an evaporating black hole where the geometrical null energy condition is expected not to hold, classical gravitons can escape from the "black hole" defined with null curves. That is, the causal structures become nontrivial. It may be one of the possible solutions for the information loss paradox of evaporating black holes.