Abstract
In the preceding paper, covariant and gauge-invariant quantities were defined that characterize density inhomogeneities in an almost-uniform model universe in a transparent way. In this paper second-order propagation equations are derived for these quantities in the case of a general "perfect fluid," and their properties examined. We do not use a harmonic decomposition in our definitions, but when such a decomposition is applied, our results are compatible with those obtained by Bardeen in his harmonically based gauge-invariant analysis. Our second-order equation enables a unified and transparent derivation of a series of results in the literature, without any ambiguity from choice of any particular gauge.
- Received 1 May 1989
DOI:https://doi.org/10.1103/PhysRevD.40.1819
©1989 American Physical Society