Cosmological aspects of the D-brane world

Abstract

The D-brane world is the idea that we are living on the D-brane imbedded in a 10- or 11-dimensional spacetime of string theory, aiming at the construction of realistic models from string theory. We investigate the cosmological aspects of the D-brane world, focusing on homogeneous anisotropic cosmology driven by the dilaton and the NS-NS 2-form field which becomes massive in the presence of the D-brane. The dilaton possesses the potential due to the presence of the D-brane, various form field fluxes, and the curvature of extra dimensions. In the absence of stabilizing potential, we found the attractor solutions for this system which show the overall features of general solutions. In the presence of non-vanishing NS-NS 2-form field, the homogeneous universe expands anisotropically while the D-brane term dominates. Isotropy is recovered as the dilaton rolls down and the curvature term dominates. With the stabilizing potential for the dilaton, the anisotropy developed by the initial NS-NS 2-form field flux is erased as the NS-NS 2-form field begins to oscillate around the minimum, forming B-matter, and an isotropic matter-dominated universe is obtained.