arXiv 1804.056932018-04-13gr-qc

修正$f(R, T)$引力场中具有体粘滞的新全息暗能量的演化和热力学

Evolution and thermodynamics of new holographic dark energy with bulk viscosity in modified $f(R, T)$ gravity

C P Singh, Milan Srivastava

备注：: 29 pages, 13 figures. arXiv admin note: text overlap with arXiv:1406.2089, arXiv:1612.00345, arXiv:1501.04047, arXiv:1002.3605, arXiv:0905.0527 by other authors

摘要：

本文在新全息暗能量（HDE）中引入体粘滞系数来描述修正的$f(R,T)$引力模型中宇宙非理想流体对宇宙演化的影响。假设$f(R,T)=R+λT$，其中$R$为Ricci标量，$T$为能量动量张量的迹，$λ$为常数，导出了体粘性形式的Hubble参数的一般函数，为粘性新HDE模型的建立提供了一个步骤.特别地，我们假设总体积粘性系数与宇宙膨胀的速度成正比，使得$ζ=ζ_0+ζ_1 H$。通过对$λ$、$ζ_0$和$ζ_1$的正负取值范围的选择，得到了尺度因子和减速参数的解，并对所有可能的情形（减速、加速及其过渡）进行了分类，分析了宇宙的演化.根据粘性项的大小，在早期或晚期有一个从减速相到加速相的过渡。对于粘性项的大值，它总是在整个演化过程中加速。此外，我们还研究了状态探测器对$\{r, s\}$和$\textit{Om}$诊断粘性新的HDE模型，以区别于其他现有的DE模型。我们的粘性模型也不同于其他现有的暗能量模型。有效状态方程参数的演化值为-0.9745，与观测值非常接近。在一定的体粘滞系数约束条件下，熵和广义热力学第二定律对该模型是成立的。分析表明，宇宙介质中的体粘滞效应可以解释这种暗能量现象。

英文摘要：

In this paper, bulk viscosity is introduced in new holographic dark energy (HDE) to describe the effects of cosmic non-perfect fluid on the evolution of the universe in modified $f(R,T)$ gravity. Assuming $f(R,T)=R+λT$, where $R$ is the Ricci scalar, $T$, the trace of energy-momentum tensor and $λ$ is a constant, we derive a general function of Hubble parameter with bulk viscous form to provide a procedure for the viscous new HDE model building. Especially, we assume the total bulk viscosity coefficient proportional to the velocity of the expansion of the universe in such a way that $ζ=ζ_0+ζ_1 H$. We obtain the solutions of the scale factor and deceleration parameter and classify all the possible scenarios (deceleration, acceleration and their transition) with different parameter regions chosen properly for positive and negative ranges of $λ$, and $ζ_0$ and $ζ_1$ to analyze the evolution of the universe. It is observed that there is a transition from decelerated phase to accelerated phase at early or late time depending on the values of viscous terms. For large values of viscous terms it always accelerates through out the evolution. Furthermore, we also investigate the statefinder pair $\{r, s\}$ and $\textit{Om}$ diagnostics for the viscous new HDE model to discriminate with other existing DE models. Our viscous model is also different from other existing dark energy models. The evolution of effective equation of state parameter is -0.9745 which is very close to the observation. The entropy and generalized second law of thermodynamics are valid for this model under some constraints of bulk viscous coefficient. The analysis shows that the dark energy phenomena may be explained as the effect of bulk viscosity in the cosmic medium.

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摘要：

英文摘要：

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