摘要

In this paper, we study the implementation of brane worlds in type II string theory. Starting with the NS/NS sector of type II string, we first compactify the (D + d(+) + d(-))-dimensional spacetime, and reduce the corresponding action to a D-dimensional effective action, where the topologies and geometries of Md+ and Md- are arbitrary. We further compactify one of the (D - 1) spatial dimensions on an S-1/Z(2) orbifold, and derive the gravitational and matter field equations both in the bulk and on the branes. Then, we investigate two key issues in such a setup: (i) the radion stability and radion mass; and (ii) the localization of gravity, and the corresponding Kaluza-Klein (KK) modes. We show explicitly that the radion is stable and its mass can be in the order of TeV. In addition, the gravity is localized on the visible brane, and its spectrum of the gravitational KK towers is discrete and can have a mass gap of TeV, too. The high order Yukawa corrections to the 4-dimensional Newtonian potential is exponentially suppressed, and can be negligible. Applying such a setup to cosmology, we obtain explicitly the field equations in the bulk and the generalized Friedmann equations on the branes.

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