A Study of Accelerating Cosmologies from Superstring/M theories
Nobuyoshi Ohta
TL;DR
This work investigates transient cosmic acceleration arising from time-dependent compactifications of vacuum solutions and S2-branes in superstring/M theories. By solving generalized S-brane configurations with internal spaces of curvature σ ∈ {+1,0,-1}, it analyzes how parameter choices affect the 4D expansion and the evolution of the internal space, finding acceleration possible even with spherical internal spaces but typically accompanied by eventual contraction and modest expansion factors. The study also connects SM2-brane and SD2-brane cosmologies via dimensional reduction, noting that SD2-brane dynamics largely mirror SM2-brane behavior while raising concerns about strong string coupling in several cases, especially for flat and spherical interiors. Collectively, the results show that time-dependent compactifications can yield transient acceleration in higher-dimensional theories, but achieving large enough expansion to address cosmological problems remains challenging, motivating exploration of more general internal geometries or parameterizations.
Abstract
We study aspects of the accelerating cosmologies obtained from the compactification of vacuum solution and S2-branes of superstring/M theories. Parameter dependence of the resulting expansion of our universe and internal space is examined for all cases. We find that accelerating expansions are obtained also from spherical internal spaces, albeit the solution enters into contracting phase eventually. The relation between the models of SM2- and SD2-branes are also discussed, and a potential problem with SD2-brane model is noted.