arXiv 1704.025012017-04gr-qc

用守恒有效流体解释$f({\sf R},{\sf T})$重力

Interpretation of $f({\sf R},{\sf T})$ gravity in terms of a conserved effective fluid

Hamid Shabani, Amir Hadi Ziaie

备注：: 21 pages, 3 figures
发表信息：: Int. J Mod. Phys. A, 33 1850050 (2018)
DOI：: 10.1142/S0217751X18500501

摘要：

本文介绍了一种从不同角度研究$f({\sf R},{\sf T})$引力理论的新方法。这里，${\sf T}$表示物质流体的能量-动量张量（{ \sf EMT}）的迹。通常的方法（如文献中所讨论的）是选择一个$h({\sf T})$函数，然后求解所得的弗里德曼方程。然而，我们的目标是，不失一般性，重新制定一个特定的类的$f({\sf R},{\sf T})$重力模型，其中爱因斯坦-希尔伯特作用是由一个任意函数的轨迹{ \sf EMT}。该策略是根据有效流体的组分重新定义运动方程。我们表明，在这种情况下，{ \sf EMT}是自动保存。我们将看到，在$f({\sf R},{\sf T})$引力中（至少）采用这样一种观点，伴随着两个重要的观点。一方面，$h({\sf T})$函数是基于物理概念选择的，另一方面，我们清楚地理解了物质在守恒有效流体方面的整体或有效行为。为了说明这个想法，我们研究了一些模型，其中不同的物理性质的有效流体归因于每个模型。特别地，我们讨论了具有常数有效密度、常数有效压力和常数有效状态方程（{ \sf EoS}）参数的模型。此外，将考虑两个模型与有效密度和有效压力之间的关系。一个很好的结果是，在$f({\sf R},{\sf T})$引力中，理想流体有可能有效地表现为具有四个自由参数的修正的Chaubergin气体。

英文摘要：

In the present work we introduce a novel approach to study $f({\sf R},{\sf T})$ gravity theory from a different perspective. Here, ${\sf T}$ denotes the trace of energy-momentum tensor ({\sf EMT}) of matter fluids. The usual method (as discussed in the literature) is to choose an $h({\sf T})$ function and then solve for the resulted Friedman equations. Nevertheless, our aim here is, without loss of generality, to reformulate a particular class of $f({\sf R},{\sf T})$ gravity models in which the Einstein-Hilbert action is promoted by an arbitrary function of the trace of {\sf EMT}. The strategy is the redefinition of the equation of motion in terms of the components of an effective fluid. We show that in this case the {\sf EMT} is automatically conserved. As we shall see, adopting such a point of view (at least) in $f({\sf R},{\sf T})$ gravity is accompanied by two significant points. On one hand, $h({\sf T})$ function is chosen based upon a physical concept and on the other, we clearly understand the overall or effective behavior of matter in terms of a conserved effective fluid. To illustrate the idea, we study some models in which different physical properties for the effective fluid is attributed to each model. Particularly, we discuss models with constant effective density, constant effective pressure and constant effective equation of state ({\sf EoS}) parameter. Moreover, two models with a relation between the effective density and the effective pressure will be considered. An elegant result is that in $f({\sf R},{\sf T})$ gravity, there is a possibility that a perfect fluid could effectively behave as a modified Chaplygin gas with four free parameters.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

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