  In this work the most promising string cosmology models are re-viewed model
by model in detail. These models are based on conceptsform string theory and
heterotic M theory to construct possible scenar-ios for the beginning and the
evolution of the universe. In all models asin standard cosmology the problem of
particle-antiparticle asymmetryarises, the issue is that all models predict
equal number of matter andantimatter to be present in the universe, this
contradicts the observa-tions that the number of antiparticle is much less than
the number ofparticles. In order to solve the asymmetry dilemma of particles
andantiparticles, it is proposed that particles and antiparticles were
dis-tributed in the brane and antibrane, respectively, immediately afterthe
collision. Implications of these scenarios are discussed in detail.
