Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
330095.pdf (Publisher version), 94KB
Ehlers, J., & Prasanna, A. R. (1996). A WKB formalism for multicomponent fields and its application to gravitational and sound waves in perfect fluids. Classical and Quantum Gravity, 13(8), 2231-2240. doi:10.1088/0264-9381/13/8/016.