Nonsingular Ekpyrotic Cosmology with a Nearly Scale-Invariant Spectrum
  of Cosmological Perturbations and Gravitational Waves
  We propose a mechanism borrowed from string theory which yields a
non-singular transition from a phase of Ekpyrotic contraction to the expanding
phase of Standard Big Bang cosmology. The same mechanism converts the initial
vacuum spectrum of cosmological fluctuations before the bounce into a
scale-invariant one, and also changes the spectrum of gravitational waves into
an almost scale-invariant one. The scalar and tensor tilts are predicted to be
the same, in contrast to the predictions from the "String Gas Cosmology"
scenario. The amplitude of the gravitational wave spectrum depends on the ratio
of the string scale to the Planck scale and may be in reach of upcoming
experiments.
