It is conjectured that in cosmological applications the particle current is not modified but finite heat or energy flow. Therefore, comoving Eckart frame is a suitable choice, as it merely ceases the charge and particle diffusion and conserves charges and particles. The cosmic evolution of viscous hadron and parton epochs in casual and non-casual Eckart frame is analyzed. By proposing equations of state deduced from recent lattice QCD simulations including pressure p, energy density $\rho$, and temperature T, the Friedmann equations are solved. We introduce expressions for the temporal evolution of the Hubble parameter $\dot{H}$, the cosmic energy density $\dot{\rho }$, and the share $\dot{\eta }$ and the bulk viscous coefficient $\dot{\zeta }$. We also suggest how the bulk viscous pressure $\mathsf{\Pi }$ could be related to H. We conclude that the relativistic theory of fluids, the Eckart frame, and the finite viscous coefficients play essential roles in the cosmic evolution, especially in the hadron and parton epochs.

中文翻译：

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Eckart因果框架中粘性QCD时代的宇宙演化

据推测，在宇宙学应用中，粒子电流没有改变，而是有限的热量或能量流。因此，共同移动Eckart框架是一个合适的选择，因为它只是停止了电荷和粒子的扩散并节省了电荷和粒子。分析了粘性和非粘性的Eckart框架中强子和parton纪元的宇宙演化。通过提出由最近的晶格QCD模拟推导的状态方程，包括压力p，能量密度$\rho$，以及温度T，求解了弗里德曼方程。我们介绍了哈勃参数随时间变化的表达式$\dot{H}$，宇宙能量密度 $\dot{\rho }$和分享 $\dot{\eta }$ 和总粘滞系数 $\dot{\zeta }$。我们还建议大块的粘性压力如何$\mathsf{\Pi }$可能与H有关。我们得出结论，流体的相对论，Eckart框架和有限粘性系数在宇宙演化中，尤其是在强子和帕顿时代中，起着至关重要的作用。