标题： 具有整体粘性流体的轴对称转变模型晚期的时间观测限制 显示英文标题

标题： Observational constraints in late time for an axially symmetric transitioning model with bulk viscous fluid

摘要： 本文研究了爱因斯坦场方程框架下具有各向同性Bianchi I型宇宙模型的轴对称情形，其中引力场的源为具有体粘性的流体，并假设体粘性压力为$-3\zeta H^2$的barotropic形式。 通过四个数据集估计了模型参数：哈勃46数据集描述了不同红移处的哈勃参数值；联合2.1编纂数据集包含了580个不同红移处的超新星Ia的距离模数；Pantheon数据集包含了1048个不同红移处的超新星Ia的视星等；最后，BAO数据集给出了5个红移处的体积平均距离。 使用传统的贝叶斯方法分析观测数据，并利用马尔可夫链蒙特卡洛(MCMC)技术得到参数的后验分布。为了获得MCMC分析的最佳拟合模型参数值，我们使用了$ emcee $包。对于参数估计，我们还采用了最小化$\chi^{2}$函数的方法。此外，我们尝试使用前面描述的四个数据集的组合数据统计得出这些值。 OHD+BAO和OHD+Pan+BAO+Union组合数据集分别提供了最佳拟合哈勃参数值$H_0$为$66.912 ^{+0.497}_{-0.501})$km/s/Mpc和$74.216 ^{+0.150}_{-0.148}$km/s/Mpc。 我们进行了状态求解器诊断以讨论暗能量的性质。还讨论了一些其他的几何参数，如jerk参数和Om诊断，以阐明暗能量模型的性质。 研究表明，该模型在晚期行为类似于五重态，并接近$\Lambda$冷暗物质(CDM)模型。 显示英文摘要

摘要： In this paper, we explore an axially symmetric Bianchi type-I model of the universe with bulk viscous fluid as a source of gravitational field under the framework of Einstein's field equations by assuming barotropic bulk viscous pressure as $-3\zeta H^2$. The model parameters have been estimated with the help of four data sets: The Hubble 46 data set describes Hubble parameter values at various redshifts, Union 2.1 compilation data sets comprise a distance modulus of 580 SNIa supernovae at different redshifts, the Pantheon data set contains Apparent magnitudes of 1048 SNIa supernovae at various redshifts and finally BAO data set of volume averaged distances at 5 redshifts. The observational data is analyzed using the traditional Bayesian methodology, and the posterior distributions of the parameters are obtained using the Markov Chain Monte Carlo (MCMC) technique. To get the best-fit values for the model parameters for MCMC analysis, we use the $ emcee $ package. For parameter estimation, we have also employed the minimizing $\chi^{2}$ function. We also tried to achieve these values statistically using combined data sets from the four described earlier. The OHD+BAO~and~OHD+Pan+BAO+Union combined data sets provide the best fit Hubble parameter value $H_0$ as $66.912 ^{+0.497}_{-0.501})$ Km/s/Mpc and $74.216 ^{+0.150}_{-0.148}$ Km/s/Mpc respectively. We have performed state finder diagnostics to discuss the nature of dark energy. Some other geometrical parameters like the Jerk parameter and the Om diagnostic are also being discussed to clarify the nature of the dark energy model. The study reveals that the model behaves like a quintessence in late time and approaches the $\Lambda$ CDM model.