Physics – High Energy Physics – High Energy Physics - Theory
Scientific paper
2004-09-24
Int.J.Mod.Phys.A21:1091-1122,2006
Physics
High Energy Physics
High Energy Physics - Theory
31 pages, 9 figures; added references, clarified a few minor points
Scientific paper
10.1142/S0217751X0602516X
The recently proposed infrared modification of gravity through the introduction of a ghost scalar field results in a number of interesting cosmological and phenomenological implications. In this paper, we derive the exact cosmological solutions for a number of scenarios where at late stages, the ghost behaves like dark matter, or dark energy. The full solutions give valuable information about the non-linear regime beyond the asymptotic first order analysis presented in the literature. The generic feature is that these ghost cosmologies give rise to smooth transitions between radiation dominated phases (or more general power-law expansions) at early epochs and ghost dark matter resp. ghost dark energy dominated late epochs. The current age of our universe places us right at the non-linear transition phase. By studying the evolution backwards in time, we find that the dominance of the ghost over ordinary baryonic matter and radiative contributions persists back to the earliest times such that the Friedmann-Robertson-Walker geometry is dictated to a good approximation by the ghost alone. We also find that the Jeans instability occurs in the ghost dark energy scenario at late times, while it is absent in the ghost dark matter scenario.
Krause Axel
Ng Siew-Phang
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