标题： 弗里德曼宇宙学与超流体 显示英文标题

标题： Friedmann cosmology with hyperfluids

摘要： 在度量仿射引力中，引力作用和物质作用不仅依赖于度量，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，其特征是能量动量张量和超动量张量。 后者定义为物质作用关于联络的变分，它编码了粒子的额外（微观）性质。 对于一个均匀且各向同性的宇宙，最近的研究表明，一般的宇宙超动量具有五个自由度：一个在标度部分，两个在剪切部分，两个在自旋部分。 当前工作的目的是对这种完美超流体在弗里德曼-勒梅特-罗伯逊-沃尔克度量下的宇宙影响进行首次系统研究。 我们采用了一个简单的模型，包括非黎曼爱因斯坦-希尔伯特引力作用加上任意超流体物质，并通过关于状态方程的不同假设，解析求解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中的对应形式一致，只是相应的指数$\mathrm{w}_{\mathrm{eff}}$和$\mathrm{w}_\rho$由于超动量修正开始有所不同。 我们获得的结果和见解非常普遍，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.