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Abstract:
We discuss the obstacles for defining a set of observable quantities analogous to an S-matrix which are needed to formulate string theory in an accelerating universe. We show that the quintessence models with the equations of state 1<w<1/3-1 < w <-1/3 have future horizons and may be no better suited to an S-matrix or S-vector description. We also show that in a class of theories with a stable supersymmetric vacuum, a system cannot relax into a zero-energy supersymmetric vacuum while accelerating if the evolution is dominated by a single scalar field with a stable potential. Thus describing an eternally accelerating universe may be a challenge for string theory as presently defined.
  • string model
  • quintessence
  • supersymmetry
  • vacuum state
  • S-matrix
  • space-time: de Sitter
  • space-time: Robertson-Walker
  • space-time: Schwarzschild
  • causality
  • astrophysics: acceleration