对称远程平行宇宙学中的大块viscous fluid：理论与实验
Bulk viscous fluid in symmetric teleparallel cosmology: theory versus experiment
摘要：
在没有宇宙学常数的情况下，广义相对论的标准公式无法解释观测到的晚期宇宙加速的机制。另一方面，通过在爱因斯坦场方程中插入宇宙学常数，可以描述宇宙加速，但宇宙学常数遇到了前所未有的微调问题。这促使人们修改爱因斯坦的广义相对论时空几何。$f(Q)$修正引力理论是广义相对论的替代理论，其中非度规标量$Q$是引力相互作用的负责候选者。本文考虑了$f(Q)$引力下的体粘宇宙流体主导的Friedmann-Lemâitre-Robertson-Walker宇宙学模型，其泛函形式为$f(Q)=αQ^n$，其中$α$和$n$是模型的自由参数.我们约束我们的模型与最近的万神殿超新星数据集的1048个数据点，哈勃数据集的31个数据点和重子声学振荡数据集组成的6个点。对于更高的红移值，很明显$f(Q)$宇宙学比标准宇宙学更好地拟合数据。我们提出了我们的减速参数与红移的演变，它正确地预测了宇宙膨胀从减速到加速阶段的过渡。给出了密度、体粘滞压力和有效状态参数方程随红移的演化。这表明宇宙流体中的体粘滞系数是获得有效驱动宇宙膨胀的负压的有效候选者。我们还考察了不同能量条件下的行为，以检验我们的宇宙学$f(Q)$模型的可行性。此外，还研究了状态探测器诊断，以区分不同的暗能量模型。
英文摘要：
The standard formulation of General Relativity Theory, in the absence of a cosmological constant, is unable to explain the responsible mechanism for the observed late-time cosmic acceleration. On the other hand, by inserting the cosmological constant in Einstein's field equations it is possible to describe the cosmic acceleration, but the cosmological constant suffers from an unprecedented fine-tunning problem. This motivates one to modify Einstein's space-time geometry of General Relativity. The $f(Q)$ modified theory of gravity is an alternative theory to General Relativity, where the non-metricity scalar $Q$ is the responsible candidate for gravitational interactions. In the present work we consider a Friedmann-Lemâitre-Robertson-Walker cosmological model dominated by bulk viscous cosmic fluid in $f(Q)$ gravity with the functional form $f(Q)=αQ^n$, where $α$ and $n$ are free parameters of the model. We constrain our model with the recent Pantheon supernovae data set of 1048 data points, Hubble data set of 31 data points and baryon acoustic oscillations data set consisting of six points. For higher values of redshift, it is clear that the $f(Q)$ cosmology better fits data than standard cosmology. We present the evolution of our deceleration parameter with redshift and it properly predicts a transition from decelerated to accelerated phases of the universe expansion. Also, we present the evolution of density, bulk viscous pressure and the effective equation of state parameter with redshift. Those show that bulk viscosity in a cosmic fluid is a valid candidate to acquire the negative pressure to drive the cosmic expansion efficiently.We also examine the behavior of different energy conditions to test the viability of our cosmological $f(Q)$ model. Furthermore, the statefinder diagnostics are also investigated in order to distinguish among different dark energy models.
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