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arXiv 1606.07959gr-qc
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$f(R,T)$引力中爱因斯坦静态宇宙的稳定性

Stability of the Einstein static Universe in $f(R,T)$ gravity

Hamid Shabani, Amir Hadi Ziaie

摘要:

爱因斯坦静态宇宙(ES)在最近提出的各种涌现方案中发挥了重要作用,以解决宇宙学标准模型的初始奇点问题。在此模型中,我们在$f(R,T)$修正引力理论的背景下研究了ES宇宙的存在性和稳定性。考虑到$f(R,T)$函数的具体形式,我们寻求代表ES态的解的存在性。使用动力系统技术与数值分析,我们发现两类解决方案:第一个总是不稳定的鞍型,而第二个总是稳定的,使其动力学行为对应于一个中心平衡点。第二类解的重要性在于,它们在构建非奇异涌现模型方面负有重大责任,在这些模型中,宇宙可能经历了过去-永恒的一系列关于这样一个初始静态的无限振荡,之后,它通过适当的物理机制进入暴胀时代。考虑特定形式的功能$f(R,T)$,我们表明,这个理论是能够提供宇宙学的解决方案,承认紧急宇宙(EU)的情况。我们还研究了上述模型的齐次标量扰动。解的稳定区域由线性状态方程(EoS)参数和将为模型引入的其他自由参数化。我们的结果表明,在$f(R,T)$重力的修改将导致稳定的解决方案是不稳定的$f(R)$重力模型。

英文摘要:

The Einstein static (ES) universe has played a major role in various emergent scenarios recently proposed in order to cure the problem of initial singularity of the standard model of cosmology. In the herein model, we study the existence and stability of ES universe in the context of $f(R,T)$ modified theories of gravity. Considering specific forms of $f(R,T)$ function, we seek for the existence of solutions representing ES state. Using dynamical system techniques along with numerical analysis, we find two classes of solutions: the first one is always unstable of the saddle type while the second is always stable so that its dynamical behavior corresponds to a center equilibrium point. The importance of the second class of solutions is due to the significant duty they have in constructing non-singular emergent models in which the universe could have experienced past-eternally, a series of infinite oscillations about such an initial static state after which, it enters through a suitable physical mechanism, to an inflationary era. Considering specific forms for the functionality of $f(R,T)$, we show that this theory is capable of providing cosmological solutions which admit emergent universe (EU) scenarios. We also investigate homogeneous scalar perturbations for the mentioned models. The stability regions of the solutions are parametrized by a linear equation of state (EoS) parameter and other free parameters that will be introduced for the models. Our results suggest that modifications in $f(R,T)$ gravity would lead to stable solutions which are unstable in $f(R)$ gravity model.

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