标题： 带有超流体的弗里德曼宇宙学 显示英文标题

标题： Friedmann cosmology with hyperfluids

摘要： 在度规-仿射引力理论中，引力作用量和物质作用量不仅依赖于度规，还依赖于独立的仿射联络。因此，物质可以被建模为一种超流体，由能量-动量张量和超动量张量共同表征。后者被定义为物质作用量相对于联络的变化，并编码了粒子的额外（微观）属性。 对于均匀且各向同性的宇宙，最近的研究表明，一般的宇宙学超动量具有五个自由度：一个与膨胀相关，两个与剪切相关，两个与自旋部分相关。 当前工作的目的是首次系统研究这种完美超流体对以弗里德曼-勒梅特-罗伯逊-沃克度规描述的宇宙的影响。 我们采用了一个简单的模型，包括非黎曼爱因斯坦-希尔伯特引力作用量以及任意的超流体物质，并通过不同的状态方程假设解析求解了单组分和多组分超动量贡献的宇宙学方程。 值得注意的是，在许多情况下，哈勃函数和能量密度的时间演化形式仍然与广义相对论的结果一致，只是相应的指标$\mathrm{w}_{\mathrm{eff}}$和$\mathrm{w}_\rho$开始由于超动量修正而有所不同。 我们得到的结果和见解非常通用，可以帮助构建有趣的模型来解决标准宇宙学中的问题。 显示英文摘要

摘要： In metric-affine gravity, both the gravitational and matter actions depend not just on the metric, but also on the independent affine connection. Thus matter can be modeled as a hyperfluid, characterized by both the energy-momentum and hypermomentum tensors. The latter is defined as the variation of the matter action with respect to the connection and it encodes extra (micro)properties of particles. For a homogeneous and isotropic universe, it was recently shown that the generic cosmological hypermomentum possesses five degrees of freedom: one in dilation, two in shear, and two in spin part. The aim of the current work is to present the first systematic study of the implications of this perfect hyperfluid on the universe with Friedmann-Lema\^itre-Robertson-Walker metric. We adopt a simple model with non-Riemannian Einstein-Hilbert gravitational action plus arbitrary hyperfluid matter, and solve analytically the cosmological equations for single and multiple component hypermomentum contributions using different assumptions about the equation of state. It is remarkable, that in a number of cases the forms of the time evolution of the Hubble function and energy density still coincide with their general relativity counterparts, only the respective indexes $\mathrm{w}_{\mathrm{eff}}$ and $\mathrm{w}_\rho$ start to differ due to the hypermomentum corrections. The results and insights we obtained are very general and can assist in constructing interesting models to resolve the issues in standard cosmology.