Related papers: The Graceful Exit Problem in String Cosmology
The graceful exit transition from a dilaton-driven inflationary phase to a decelerated Friedmann-Robertson-Walker era requires certain classical and quantum corrections to the string effective action. Classical corrections can stabilize a…
Classical string cosmology consists of two branches related to each other by scale-factor duality: a super-inflation branch and a Friedmann-Robertson-Walker (FRW) branch. Curvature and string coupling singularity separates the two branches,…
String cosmology solutions are examined in a generalized phase-space including sources representing arbitrary corrections to lowest order string-dilaton-gravity effective action. We find a set of necessary conditions for a graceful exit…
We reexamine the graceful exit problem in the Pre-Big-Bang inflationary scenario. The dilaton-gravity action is generalized by adding the axion and a general axion/dilaton potential. We provide a phase space analysis of the dynamics which…
We construct, for the first time, a model of graceful exit transition from a dilaton-driven inflationary phase to a decelerated Friedman-Robertson-Walker era. Exploiting a demonstration that classical corrections can stabilize a high…
A broad class of two-dimensional loop-corrected dilaton gravity models exhibit cosmological solutions that interpolate between the string perturbative vacuum and a background with asymptotically flat metric and linearly growing dilaton. The…
We briefly review the status of the ``graceful exit'' problem in superstring cosmology and present a possible resolution. It is shown that there exists a solution to this problem in two-dimensional dilaton gravity provided quantum…
We examine the string cosmology equations with a dilaton potential in the context of the Pre-Big Bang Scenario with the desired scale factor duality, and give a generic algorithm for obtaining solutions with appropriate evolutionary…
We study the classical equations of motion and the corresponding Wheeler-De Witt equation for tree level string effective action with the dilaton and axion. The graceful exit problem in certain cases is then analysed.
We analyze the problem of graceful exit from superinflationary pre-big bang phase of string cosmology within the context of lowest-order string effective action. The previous no go theorems are generalized for the case when higher genus…
Within the context of a super-critical (Liouville) string, we discuss (target-space) two-dimensional string cosmology. A numerical analysis indicates that the identification of time with the Liouville mode results in an expanding universe…
We investigate the tachyon-dilaton-metric system to study the "graceful exit" problem in string theoretic inflation, where tachyon plays the role of the scalar field. From the phase space analysis, we find that the inflationary phase does…
We consider the theory obtained by adding to the usual string frame dilaton gravity action specially constructed higher derivative terms motivated by the limited curvature construction of [MukhanovET1992a] and determine the spatially…
A no-go theorem pertaining to the graceful exit problem in Pre-Big-Bang inflation is reviewed. It is shown that dilaton self-interactions and string fluid sources fail to facilitate branch changing necessary to avoid singularities. A…
We consider the problem of constructing a non-singular inflationary universe in stringy gravity via branch changing, from a previously superexponentially expanding phase to an FRW-like phase. Our approach is based on the phase space…
We consider a phenomenological modification of the Pre Big Bang scenario using ideas from the resolution of curvature singularities in Loop Quantum Cosmology. We show that non-perturbative Loop modifications to the dynamics, arising from…
The cosmological evolution of the string landscape is expected to consist of multiple stages of old inflation with large cosmological constant ending by tunnelling. Old inflation has a well known graceful exit problem as the observable…
We study the evolution of fluctuations in a universe dominated by a scalar field coupled to the Gauss-Bonnet term. During the graceful exit, we found non-negligible enhancements of both curvature perturbation and gravitational wave in the…
We re-examine the graceful exit problem in the pre-big bang scenario of string cosmology, by considering the most general time-dependent classical correction to the Lagrangian with up to four derivatives. By including possible forms for…
`Old' String Theory is a theory of one-dimensional extended objects, whose vibrations correspond to excitations of various target-space field modes including gravity. In these lectures I will give an introduction to low-energy Effective…