Ghost Dark Matter

Abstract

We revisit ghost dark matter, the possibility that ghost condensation may serve as an alternative to dark matter. In particular, we investigate the Friedmann-Robertson-Walker (FRW) background evolution and the large-scale structure (LSS) in the $\Lambda$GDM universe, i.e. a late-time universe dominated by a cosmological constant and ghost dark matter. The FRW background of the $\Lambda$GDM universe is indistinguishable from that of the standard $\Lambda$CDM universe if $M\gtrsim 1\mathrm{eV}$, where $M$ is the scale of spontaneous Lorentz breaking. From the LSS we find a stronger bound: $M\gtrsim 10\mathrm{eV}$. For smaller $M$, ghost dark matter would have non-negligible sound speed after the matter-radiation equality, and thus the matter power spectrum would significantly differ from observation. These bounds are compatible with the phenomenological upper bound $M\lesssim 100\mathrm{GeV}$ known in the literature.

27 pages, 5 figures, accepted for publication in JCAP

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• The Cosmological Dipole in Tilted Anisotropic Universes