## Two-Fluid Viscous Modified Gravity on a RS Brane

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Brevik, Iver

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Singularities in the dark energy late universe are discussed, under the
assumption that the Lagrangian contains the Einstein term R plus a modified
gravity term R^\alpha, where \alpha is a constant. The 4D fluid is taken to be
viscous and composed of two components, one Einstein component where the bulk
viscosity is proportional to the scalar expansion \theta, and another modified
component where the bulk viscosity is proportional to the power
\theta^{2\alpha-1}. Under these conditions it is known from earlier that the
bulk viscosity can drive the fluid from the quintessence region (w > -1) into
the phantom region (w<-1), where w is the thermodynamical parameter [I. Brevik,
Gen. Rel. Grav. 38, 1317 (2006)]. We combine this 4D theory with the 5D
Randall-Sundrum II theory in which there is a single spatially flat brane
situated at y=0. We find that the Big Rip singularity, which occurs in 4D
theory if \alpha >1/2, carries over to the 5D metric in the bulk, |y|>0. The
present investigation generalizes that of an earlier paper [I. Brevik,
arXiv:0807.1797; to appear in Eur. Phys. J. C] in which only a one-component
modified fluid was present.

Comment: 8 pages, no figures; to appear in Gravitation & Cosmology

Comment: 8 pages, no figures; to appear in Gravitation & Cosmology

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General Relativity and Quantum Cosmology