Pre-big-bang in string cosmology

Abstract

The duality-type symmetries of string cosmology naturally lead us to expect a pre-big-bang phase of accelerated evolution as the dual counterpart of the decelerating expansion era of standard cosmology. Several properties of this scenario are discussed, including the possibility that it avoids the initial singularity and that it provides a large amount of inflation. We also discuss how possible tracks of the pre-big-bang era may be looked for directly in the spectral and "squeezing" properties of relic gravitons and, indirectly, in the distorsion they induce on the cosmic microwave background.

Isotropization in brane gas cosmology

“…[6,8] for recent but incomplete reviews). Beginning with the work on Pre-Big-Bang cosmology [9,10] it was realized that a dynamical dilaton should play an important role in the very early Universe. More recently, models have become prominent in which our Universe consists of a 3-brane embedded in a higher dimensional bulk space, with the standard model constrained to live on the brane [11][12][13][14][15][16][17].…”

String Cosmology: The pre-Big Bang Scenario

“…This new kind of inflation (characterized by growing H and φ) has been termed dilaton-driven inflation (DDI). The basic idea of pre-big bang cosmology [14,15,16,17] is thus illustrated in Fig. 2: the dilaton started at very large negative values (where it was practically massless), ran over a potential hill, and finally reached, sometime in our recent past, its final destination at the bottom of its potential (φ = φ 0 ).…”

Self-T-dual brane cosmology and the cosmological constant problem

“…These equations can be easily solved if we assume that V is an exponential function ofφ. Potentials of this type were first introduced in the context of string cosmology in order to obtain a regular curvature bounce [19]- [20]. In general, such potentials are not invariant under general coordinate transformations.…”

“…As in the static case, the solution associated to σ(z b ) corresponds to a negative energy density on the brane. To cope with this problem, we follow the model proposed in [8], and we assume that 20) where ρ, π, and F are treated as functions of τ . By further imposing thatρ = ρ and π = π , we separate a T-dual invariant matter contribution from a time-dependent tension.…”