  We study how the introduction of a 2-form field flux modify the dynamics of a
T-duality invariant string gas cosmology model of Greene, Kabat and Marnerides.
It induces a repulsive potential term in the effective action for the scale
factor of the spacial dimensions. Without the 2-form field flux, the universe
fails to expand when the pressure due to string modes vanishes. With the
presence of a homogeneous 2-form field flux, it propels 3 spacial dimensions to
grow into a macroscopic 4 dimensional space-time. We find that it triggers an
expansion of a universe away from the oscillating phase around the self-dual
radius. We also investigate the effects of a constant 2-form field. We can
obtain an expanding 4 dimensional space-time by tuning it at the critical
value.
