标题： 宇宙扰动在长波长极限下的演化 显示英文标题

标题： Evolution of Cosmological Perturbations in the Long Wavelength Limit

摘要： 对于空间平坦宇宙模型上的标量扰动，研究了宇宙扰动方程解的长波长极限与精确均匀背景方程解的扰动之间的关系。 结果表明，当物质仅由标量场组成时，只有当均匀扰动满足对应于动量约束的附加条件时，该均匀扰动才会与某些非均匀扰动的长波长极限一致。 相反，如果描述物质的基本变量包含矢量场，如流体的情况，则不会出现这样的约束。 此外，作为这一一般分析的副产品，结果表明在长波长极限下，扰动方程存在两个普遍的精确解，这些解仅用背景量来表示。 它们代表绝热增长和衰减模式，并对应于完美流体系统和标量场系统的已知精确解。 显示英文摘要

摘要： The relation between the long wavelength limit of solutions to the cosmological perturbation equations and the perturbations of solutions to the exactly homogeneous background equations is investigated for scalar perturbations on spatially flat cosmological models. It is shown that a homogeneous perturbation coincides with the long wavelength limit of some inhomogeneous perturbation only when the former satisfies an additional condition corresponding to the momentum constraint if the matter consists only of scalar fields. In contrast, no such constraint appears if the fundamental variables describing the matter contain a vector field as in the case of a fluid. Further, as a byproduct of this general analysis, it is shown that there exist two universal exact solutions to the perturbation equations in the long wavelength limit, which are expressed only in terms of the background quantities. They represent adiabatic growing and decaying modes, and correspond to the well-known exact solutions for perfect fluid systems and scalar field systems.