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Acoustics of early universe. II. Lifshitz vs. gauge-invariant theories

Zdzislaw A. Golda, Andrzej Woszczyna

gr-qcarXiv:gr-qc/0002051

Abstract

Appealing to classical methods of order reduction, we reduce the Lifshitz system to a second order differential equation. We demonstrate its equivalence to well known gauge-invariant results. For a radiation dominated universe we express the metric and density corrections in their exact forms and discuss their acoustic character.

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