标题： 单模引力宇宙扰动中的规范固定 显示英文标题

标题： Gauge fixing in cosmological perturbations of Unimodular Gravity

摘要： 聚焦于物质和几何线性扰动的宇宙学演化，我们在单模引力框架内计算出了与牛顿规范和同步规范等价的表达式，这两种规范通常被广泛使用并实现于玻尔兹曼代码中。 我们分析的一个重要方面是包含了能动量流的破坏及其扰动。 此外，我们首次证明了这两种规范可以被一致地固定下来，尽管正如先前文献中已经注意到的那样，在物质和度规涨落的动力学意义上，这两种规范都无法还原为广义相对论中的情形。 具体来说，我们表明由于单模约束在一级扰动水平上只导致度规涨落标量模式的单一自由度，因此单模引力的动力学迫使我们在牛顿规范中保留各向异性应力，而在同步规范中冷暗物质的共动参考系无法设定。 我们回顾了冷暗物质密度对比的物理意义，并得到了 Sachs-Wolfe 效应并与单模引力中宇宙扰动的已有文献结果进行了比较。 显示英文摘要

摘要： With focus on the cosmological evolution of linear perturbations of matter and geometry, we calculate the equivalent expressions to that of the Newtonian and Synchronous gauges within the framework of Unimodular Gravity, being these two gauges commonly used and implemented in Boltzmann codes. An important aspect of our analysis is the inclusion of the energy-momentum current violation, as well as its perturbations. Moreover, for the first time we demonstrate that it is possible to fix both gauges consistently, although as it has been already noticed in previous literature, neither of them is recovered in the sense of the dynamics given in General Relativity for matter and metric fluctuations. Specifically, we show that since the unimodular constraint at the level of linear perturbations lead to only one degree of freedom of scalar modes of metric fluctuations, the dynamics in Unimodular Gravity forces to keep the anisotropic stress in the Newtonian gauge, whereas the cold dark matter comoving frame can not be set in the Synchronous gauge. The physical implications on the density contrast of cold dark matter is reviewed, and the Sachs-Wolfe effect is obtained and compared with previous results in the literature of cosmological perturbations in Unimodular Gravity.