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Paper   IPM / P / 12277
School of Physics
  Title:   Revisiting Cosmic No-Hair Theorem for Inflationary Settings
1.  A. Maleknejad
2.  M.M. Sheikh-Jabbari
  Status:   Published
  Journal: Phys. Rev. D
  Vol.:  85
  Year:  2012
  Pages:   123508
  Supported by:  IPM
In this work we revisit Wald's cosmic no-hair theorem in the context of accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing anisotropic stress tensor and when the fluid energy momentum tensor is of the form of a cosmological constant term plus a piece which does not respect strong or dominant energy conditions. Such a fluid is the one appearing in inflationary models. We show that for such a system anisotropy may grow, in contrast to the cosmic no-hair conjecture. In particular, for a generic inflationary model we show that there is an upper bound on the growth of anisotropy. For slow-roll inflationary models our analysis can be refined further and the upper bound is found to be of the order of slow-roll parameters. We examine our general discussions and our extension of Wald's theorem for three classes of slow-roll inflationary models, generic multi-scalar field driven models, anisotropic models involving U(1) gauge fields and the gauge-flation scenario.

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