Fluxes in string/brane gas cosmology ストリング/ブレーンガス宇宙論におけるフラックスの効果
Fluxes in string/brane gas cosmology
Rosas Lopez Igmar Cedrell
ロサス ロペス イグマール セドレル
In this work we study how the introduction of a two-form field flux modifies the dynamics of string gas cosmology in different schemes. In chapter 1, we give a short introduction to the string gas cosmology model. In chapter 2 we present the T-duality invariant string gas cosmology modelof Greene, Kabat and Marnerides which replaces the Newtonian-like kinetic terms in the dilaton gravity action by their relativistic counterparts. We introduce the contribution of the two-form field into this model. The two-form flux induces a repulsive potential term in the effective action for the scale factor of the spatial dimensions. Without the two-form field flux, the universe fails to expand when the pressure due to string modes vanishes. With the presence of a homogeneous two-form field flux, it propels 3 spatial 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. Using the same model we also investigate the effects of a constant two-form field. We can obtain an expanding 4 dimensional space-timeby tuning it at the critical value. In chapter 3 we investigate the behaviour of the two-form field in two different models equipped with a moduli stabilization mechanism. The first model uses D-branes, NS5 branes and KK5 monopoles in order to fix the moduli. A simplified KK5-D1 with a two-form field is analyzed. We include the two-form field into the system and conclude that the dilaton is no longer stabilized in this extended model. The second scheme we study consist of a cosmology in which the moduli are fixed using superpotentials. We assume a situation where all the moduli have been fixed except the radion. We find that the inclusion of a two-form field in the action gives a contribution to the effective potential of the radion that helps enhance the stabilization mechanism.