相关论文: Nonsingular global string compactifications

Aspects of string cosmology for critical and non-critical strings are discussed emphasizing the necessity to account for the dilaton dynamics for a proper incorporation of ``large - small" duality. This drastically modifies the intuition…

We review various aspects of de Sitter spacetime in string theory: its status as an effective field theory spacetime solution, its relation to the vacuum energy problem in string theory, its (global) holographic definition in terms of two…

The vanishing of the cosmological constant and absence of a massless dilaton might be explained by a duality between a supersymmetric string vacuum in three dimensions and a non-supersymmetric string vacuum in four dimensions.

Assuming the four-dimensional space-time to be a general warped product of two surfaces we reduce the four-dimensional Einstein equations to a two-dimensional problem which can be solved. All global vacuum solutions are explicitly…

We review a recently proposed approach to construct superstring cosmological evolutions, which are free of Hagedorn instabilities and initial singularities. We illustrate these ideas in hybrid models in two dimensions.

We present full numerical solutions to the system of a global string embedded in a six-dimensional space time. The solutions are regular everywhere and do confine gravity in our four-dimensional world. They depend on the value of the…

Non-singular two and three dimensional string cosmologies are constructed using the exact conformal field theories corresponding to SO(2,1)/SO(1,1) and SO(2,2)/SO(2,1). All semi-classical curvature singularities are canceled in the exact…

In a previous paper (hep-th/0509067) using matrix model, we showed that closed string tachyons can resolve spacelike singularity in one particular class of Misner space (with anti-periodic boundary conditions for fermions around the spatial…

We consider a class of higher order corrections with arbitrary power $n$ of the curvature tensor to the standard gravity action in arbitrary space-time dimension $D$. The corrections are in the form of Euler densities and are unique at each…

We study the behavior of a general gravitational action, including quadratic terms in the curvature, supplemented by a compact scalar field in 4+1 dimensions. The generalized Einstein equation for this system admits solutions which are…

Accelerating universe or the existence of a small and positive cosmological constant is probably the most pressing obstacle as well as opportunity to significantly improving the models of four-dimensional cosmology from fundamental theories…

In order for spacetimes with static extra dimensions to have 4-dimensional de Sitter expansion they must have at least positive curvature, warping sourced by the 4-d expansion, or violate the null energy condition everywhere in the extra…

In this work cosmological models are considered for the low energy string cosmological effective action (tree level) in the absence of dilaton potential. A two parametric non-diagonal family of analytic solutions is found. The curvature is…

We discuss time - dependent solutions of the leading order string effective equations for a non-zero central charge deficit and curved maximally symmetric space. Some regular solutions are found for the case of non-trivial antisymmetric…

In a general superstring vacuum configuration, the `internal' space (sector) varies in spacetime. When this variation is non-trivial only in two space-like dimensions, the vacuum contains static cosmic strings with finite energy per unit…

In spacetimes with compact dimensions there exist several black object solutions including the black-hole and the black-string. These solutions may become unstable depending on their relative size and the relevant length scale set by the…

We consider the gauge dyonic string solution of the K3 compactified heterotic string theory in a four dimensional cosmological context. Since for this solution Green-Schwarz as well as Chern-Simons corrections have been taken into account…

We consider the spacetime dynamics of a gas of closed strings in the context of General Relativity in a background of arbitrary spatial dimensions. Our motivation is primarily late time String Gas Cosmology, where such a spacetime picture…

The implications of string theory for understanding the dimension of uncompactified spacetime are investigated. Using recent ideas in string cosmology, a new model is proposed to explain why three spatial dimensions grew large. Unlike the…

The dynamics of the early universe may have been profoundly influenced by spatial anisotropies. A search for such backgrounds in the context of string cosmology has uncovered the existence of an entire class of (spatatially) homogeneous but…