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Session 86 - Cosmology: Theory.
Display session, Friday, January 09
We examine the gravitational instability of two interpenetrating, barotropic fluids interacting only through gravity. Previous work on the problem (Fridman and Polyachenko, 1984) indicates that two fluids with initial relative motion are unstable to small perturbations at all wavenumbers in some range of Mach numbers. We expand upon these results by exploiting the analogy between this problem and the two-stream instability of plasma physics, and demonstrate the existence of negative energy modes from the indefiniteness of the energy functional. This allows for explosive nonlinear growth even in situations for which the linear theory predicts absolute stability. We further investigate the effects of negative energy modes in a non-conservative situation where one of the fluids is radiatively damped.
reference: "Physics of Gravitating Systems I and II," by A.M. Fridman amp; V.L. Polyachenko, Springer-Verlag, 1984.
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