标题： 宇宙扰动理论与大尺度极限下的守恒量 显示英文标题

标题： Cosmological perturbation theory and conserved quantities in the large-scale limit

摘要： 重新考虑了一个几乎均匀且各向同性的完美流体宇宙的线性宇宙扰动理论，并通过引入具有物理意义的新协变和规范不变变量（这些变量定义在恒膨胀、恒曲率或恒能量密度的超曲面上）进行了形式上的简化。 讨论了大于哈勃尺度的扰动量的守恒性。 在平坦背景宇宙中，大尺度上守恒的量可以用恒膨胀超曲面上的能量密度的空间梯度的分数表示，或者反之亦然，也可以借助恒能量密度超曲面上的膨胀或曲率扰动变量来表示。 对于非零背景曲率的情况，最适于用恒曲率超曲面上的能量密度扰动来描述扰动的动力学。 显示英文摘要

摘要： The linear cosmological perturbation theory of an almost homogeneous and isotropic perfect fluid universe is reconsidered and formally simplified by introducing new covariant and gauge-invariant variables with physical interpretations on hypersurfaces of constant expansion, constant curvature or constant energy density. The existence of conserved perturbation quantities on scales larger than the Hubble scale is discussed. The quantity which is conserved on large scales in a flat background universe may be expressed in terms of the fractional, spatial gradient of the energy density on constant expansion hypersurfaces or, alternatively, with the help of expansion or curvature perturbation variables on hypersurfaces of constant energy density. For nonvanishing background curvature the perturbation dynamics is most suitably described in terms of energy density perturbations on hypersurfaces of constant curvature.