Dilaton Stabilization in (A)dS Spacetime with Compactified Dimensions

We investigate dilaton stabilization in a higher-dimensional theory. The background geometry is based on an eleven-dimensional Kaluza-Klein/supergravity model, which is assumed to be a product of four-dimensional de Sitter (dS_4) spacetime and a seven sphere. The dilaton potential has a local minimum resulting from contributions of the cosmological constant, the curvature of the internal spacetime and quantum effects of the background scalar, vector, spinor, and tensor fields. The dilaton settles down to the local minimum, and the scale of the extra dimensions eventually become time independent. Our four-dimensional universe evolves from dS_4 into AdS_4 after stabilization of the extra dimension.Comment: 43 pages, 12 figures, PTPTeX. Accepted for publication in Progress of Theoretical Physic

Cosmology in p-brane systems

We present time-dependent solutions in the higher-dimensional gravity which are related to supergravity in the particular cases. Here, we consider p-branes with a cosmological constant and the intersections of two and more branes. The dynamical description of p-branes can be naturally obtained as the extension of static solutions. In the presence of a cosmological constant, we find accelerating solutions if the dilaton is not dynamical. In the case of intersecting branes, the field equations normally indicate that time-dependent solutions in supergravity can be found if only one harmonic function in the metric depends on time. However, if the special relation between dilaton couplings to antisymmetric tensor field strengths is satisfied, one can find a new class of solutions where all harmonic functions depend on time. We then apply our new solutions to study cosmology, with and without performing compactifications.Comment: 45 pages, typos corrected, references are improve

Dynamical brane with angles : Collision of the universes

We present the time-dependent solutions corresponding to the dynamical D-brane with angles in ten-dimensional type II supergravity theories. Our solutions with angles are different from the known dynamical intersecting brane solutions in supergravity theories. Because of our ansatz for fields, all warp factors in the solutions can depend on time. Applying these solutions, we construct cosmological models from those solutions by smearing some dimensions and compactifying the internal space. We find the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological solutions with power-law expansion. We also discuss the dynamics of branes based on these solutions. When the spacetime is contracting in ten dimensions, each brane approaches the others as the time evolves. However, for Dp-brane ($p\le 7$) without smearing branes, a singularity appears before branes collide. In contrast, the D6-D8 brane system or the smeared D(p-2)-Dp brane system with one uncompactified extra dimension can provide an example of colliding branes (and collision of the universes), if they have the same charges.Comment: 34 pages, 8 figure

Dynamical solution of supergravity

We present a class of dynamical solutions for an intersecting D4-D8 brane system in ten-dimensional type IIA supergravity. The dynamical solutions reduces to a static warped AdS_6 x S^4 geometry in a certain spacetime region. We also consider lower-dimensional effective theories for the warped compactification of general p-brane system. It is found that an effective (p+1)-dimensional description is not possible in general due to the entanglement of the transverse coordinates and the (p+1)-dimensional coordinates in the metric components. Then we discuss cosmological solutions. We find a solution that behaves like a Kasner-type cosmological solution at $\tau\to\infty$, while it reduces to a warped static solution at $\tau\to0$, where $\tau$ is the cosmic time.Comment: 4 pages, no figure. Contribution to proceedings of the workshop "The 17th Workshop on General Relativity and Gravitation" (Japan, December 2007