Title: Dark matter perturbations and viscosity: a causal approach Show Chinese title

Title: 暗物质扰动与粘性：一种因果方法

Abstract: The inclusion of dissipative effects in cosmic fluids modifies their clustering properties and could have observable effects on the formation of large scale structures. We analyse the evolution of density perturbations of cold dark matter endowed with causal bulk viscosity. The perturbative analysis is carried out in the Newtonian approximation and the bulk viscosity is described by the causal Israel-Stewart (IS) theory. In contrast to the non-causal Eckart theory, we obtain a third order evolution equation for the density contrast that depends on three free parameters. For certain parameter values, the density contrast and growth factor in IS mimic their behaviour in $\Lambda$CDM when $z \geq 1$. Interestingly, and contrary to intuition, certain sets of parameters lead to an increase of the clustering. Show Chinese abstract

Abstract: 宇宙流体中包含耗散效应会改变它们的聚类性质，并可能对大尺度结构的形成产生可观测的影响。 我们分析了具有因果黏性系数的冷暗物质密度扰动的演化。 扰动分析是在牛顿近似下进行的，黏性系数由因果性的以色列-斯图尔特（Israel-Stewart, IS）理论描述。 与非因果性的Eckart理论不同，我们得到了一个三阶的密度对比度演化方程，该方程依赖于三个自由参数。 对于某些参数值，IS中的密度对比度和增长因子在$\Lambda$CDM 中$z \geq 1$时表现出类似的行为。 有趣的是，与直觉相反，某些参数集会导致聚类增强。