  We investigate the spectrum of cosmological perturbations in a bounce cosmos
modeled by a scalar field coupled to the string tachyon field (CSTB cosmos). By
explicit computation of its primordial spectral index we show the power
spectrum of curvature perturbations, generated during the tachyon matter
dominated contraction phase, to be nearly scale invariant. We propose a unified
space of parameters for a systematic study of inflationary/bouncing
cosmologies. We find that CSTB cosmos is dual--in Wands's sense--to the
slow-roll inflation model as can be easily seen from this unified parameter
space. Guaranteed by the dynamical attractor behavior of CSTB Cosmos, this
scale invariance is free of the fine-tuning problem, in contrast to the
slow-roll inflation model.
