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arXiv 2009.04353gr-qc
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扩展的遥平行引力理论的聚焦条件

Focusing conditions for extended teleparallel gravity theories

U. K. Beckering Vinckers, A. de la Cruz-Dombriz, F. J. Maldonado Torralba

摘要:

在远程平行引力扩展理论$f(T)$的背景下,我们推导出Levi-Civita连接的类时自平行线的单参数依赖同余的聚焦条件。在考虑空间平坦的罗伯逊-沃克时空之前,我们还考虑了一般度规张量的$f(T)$场方程。在此之后,我们研究了Levi-Civita联络的类时自平行曲线的单参数相依同余的扩张率。考虑到测试粒子遵循Levi-Civita连接的自动平行,使用无挠Raychaudhuri方程来确定所需的聚焦条件。最后研究了三个$f(T)$范式宇宙学模型的聚焦条件,并讨论了这些条件的满足与违背。通过这一点,我们发现$f(T)$模型,允许弱和强聚焦条件得到满足或违反。提到的是,这种行为也可以在所谓的$f(R)$和$f(Q)$理论中找到。

英文摘要:

In the context of extended theories of teleparallel gravity $f(T)$ we derive the focusing conditions for a one-parameter dependent congruence of timelike auto-parallels of the Levi-Civita connection. We also consider the $f(T)$ field equations for a general metric tensor before moving on to consider a spatially flat Robertson-Walker space-time. Following this, we study the expansion rate for a one-parameter dependent congruence of timelike auto-parallel curves of the Levi-Civita connection. Given the fact that test particles follow auto-parallels of the Levi-Civita connection, the torsion-free Raychaudhuri equation is used in order to determine the desired focusing conditions. Finally we study the obtained focusing conditions for three $f(T)$ paradigmatic cosmological models and discuss the satisfaction or violation of these conditions. Through this, we find $f(T)$ models that allow for the weak and strong focusing conditions to be satisfied or violated. It is mentioned that this behaviour can also be found in the so-called $f(R)$ and $f(Q)$ theories.

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