Problems with propagation and time evolution in f ( T ) gravity
Problems with propagation and time evolution in f ( T ) gravity
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DOI：
10.1103/physrevd.88.024019
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发表时间：
2013-03
影响因子：
5
通讯作者：
Y. Ong;K. Izumi;J. M. Nester;Pisin Chen
中科院分区：
文献类型：
--
作者：
Y. Ong;K. Izumi;J. M. Nester;Pisin Chen
引力的遥平行理论有着悠久的历史。它们包括一种特殊的情况，称为广义相对论的远程平行等价物（TEGR，又名GR$_{\|}$）。最近这个理论被推广到f（T）引力。来自观测的严格约束表明，f（T）引力并不像最初希望的那样强大。这可能暗示了迄今为止在理论层面上尚未发现的问题。在这项工作中，我们指出，一个通用的f（T）理论可以预期有一定的问题，包括超光速传播模式，其中的存在可以通过使用的特征方程，管理的动态f（T）引力和/或哈密顿结构的理论，通过狄拉克约束分析揭示。我们用几个简单规范场理论的例子来解释这种超光速模式是如何产生的。我们还指出了在f（T）引力下FLRW时空中的常时超曲面的柯西发展问题。从FLRW（作为特例，闵可夫斯基时空）初始条件的时间演化不是唯一的。
Teleparallel theories of gravity have a long history. They include a special case referred to as the Teleparallel Equivalent of General Relativity (TEGR, aka GR$_{\|}$). Recently this theory has been generalized to f(T) gravity. Tight constraints from observations suggest that f(T) gravity is not as robust as initially hoped. This might hint at hitherto undiscovered problems at the theoretical level. In this work, we point out that a generic f(T) theory can be expected to have certain problems including superluminal propagating modes, the presence of which can be revealed by using the characteristic equations that govern the dynamics in f(T) gravity and/or the Hamiltonian structure of the theory via Dirac constraint analysis. We use several examples from simpler gauge field theories to explain how such superluminal modes could arise. We also point out problems with the Cauchy development of a constant time hypersurface in FLRW spacetime in f(T) gravity. The time evolution from a FLRW (and as a special case, Minkowski spacetime) initial condition is not unique.