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Paper   IPM / Physic / 8035
School of Physics
  Title:   What Is Needed of A Tachyon If It Is to Be the Dark Energy?
1.  E.J. Copeland
2.  M.R. Garousi
3.  M. Sami
4.  S. Tsujikawa
  Status:   Published
  Journal: Phys. Rev. D
  Vol.:  71
  Year:  2005
  Pages:   043003
  Supported by:  IPM
We study a dark energy scenario in the presence of a tachyon field ϕ with potential V(ϕ) and a barotropic perfect fluid. The cosmological dynamics crucially depends on the asymptotic behavior of the quantity λ = −MpVϕ/V3/2. If λ is a constant, which corresponds to an inverse square potential V(ϕ) ∝ ϕ−2, there exists one stable critical point that gives an acceleration of the universe at late times. When λ→ 0 asymptotically, we can have a viable dark energy scenario in which the system approaches an "instantaneous" critical point that dynamically changes with λ. If |λ| approaches infinity asymptotically, the universe does not exhibit an acceleration at late times. In this case, however, we find an interesting possibility that a transient acceleration occurs in a regime where |λ| is smaller than of order unity.

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