Dynamical Selection of the Primordial Density Fluctuation Amplitude
  In inflationary models, the predicted amplitude of primordial density
perturbations Q is much larger than the observed value (~10^{-5}) for natural
choices of parameters. To explain the requisite exponential fine-tuning,
anthropic selection is often invoked, especially in cases where microphysics is
expected to produce a complex energy landscape. By contrast, we find examples
of ekpyrotic models based on heterotic M-theory for which dynamical selection
naturally favors the observed value of Q.
