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arXiv 0904.2774gr-qcastro-ph.COhep-th
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f(R)引力、挠率和非度量性

f(R) gravity, torsion and non-metricity

Thomas P. Sotiriou

摘要:

对于具有独立对称连接(无挠率)的f(R)引力理论,通常称为帕拉蒂尼f(R)引力理论,以及具有挠率但无非度规性的f(R)引力理论,称为U4理论,已经证明,独立连接实际上可以代数地消除,只要这种连接不耦合到物质。值得注意的是,在这两种情况下的结果是相同的理论,这是动态等价的ω_0=-3/2 Brans-Dicke理论。它表明,即使是最一般的情况下,一个独立的联系与非度规性和扭转之一,达到完全相同的理论,在更严格的情况下。这推广了以前的结果,并解释了为什么假设挠率或非度规性为零最终会导致相同的理论。它还表明,f(R)作用量不能支持一个带有动力学自由度的独立连接,不管这个连接有多普遍,至少只要没有连接-物质耦合。

英文摘要:

For both f(R) theories of gravity with an independent symmetric connection (no torsion), usually referred to as Palatini f(R) gravity theories, and for f(R) theories of gravity with torsion but no non-metricity, called U4 theories, it has been shown that the independent connection can actually be eliminated algebraically, as long as this connection does not couple to matter. Remarkably, the outcome in both case is the same theory, which is dynamically equivalent with an ω_0=-3/2 Brans--Dicke theory. It is shown here that even for the most general case of an independent connection with both non-metricity and torsion one arrives at exactly the same theory as in the more restricted cases. This generalizes the previous results and explains why assuming that either the torsion or the the non-metricity vanishes ultimately leads to the same theory. It also demonstrates that f(R) actions cannot support an independent connection which carries dynamical degrees of freedom, irrespectively of how general this connection is, at least as long as there is no connection-matter coupling.

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