Uniqueness of Current Cosmic Acceleration
  One of the strongest arguments against the cosmological constant as an
explanation of the current epoch of accelerated cosmic expansion is the
existence of an earlier, dynamical acceleration, i.e. inflation. We examine the
likelihood that acceleration is an occasional phenomenon, putting stringent
limits on the length of any accelerating epoch between recombination and the
recent acceleration; such an epoch must last less than 0.05 e-fold (at z>2) or
the matter power spectrum is modified by more than 20%.
