Stabilizing the dilaton in superstring cosmology

Abstract

We address the important issue of stabilizing the dilaton in the context of superstring cosmology. Scalar potentials which arise out of gaugino condensates in string models are generally exponential in nature. In a cosmological setting this allows for the existence of quasiscaling solutions, in which the energy density of the scalar field can, for a period, become a fixed fraction of the background density, due to the friction of the background expansion. Eventually the field can be trapped in the minimum of its potential as it leaves the scaling regime. We investigate this possibility in various gaugino condensation models and show that stable solutions for the dilaton are far more common than one would have naively thought. ͓S0556-2821͑98͒01320-4͔

Quintessence models in supergravity

“…In this scenario, the Kähler potential acquires string inspired non-perturbative corrections. A further nice feature of these models is that it is possible to have a minimum with zero or small positive cosmological constant [13,15], and moreover it is possible to establish that the dilaton can be stabilized in such a minimum in a cosmological setting [16].…”

Moduli entrapment with primordial black holes

“…Their energy density dilutes as ρ h ∼ 1/a 6 for the homogeneous mode or as ρ i ∼ 1/a 4 for inhomogeneities [24], where a is the cosmological scale factor. Some aspects of more phenomenologically motivated, but similar, mechanisms have also been discussed in [25,26,27].…”

“…Thus this initial regime is of very little interest to start with. One has to make some choices of the initial conditions, and the whole purpose of the resolutions of the overshoot problem here and in [19,20,21,26,27] is to demonstrate that the favorable initial region may be likely: in this case, it is a finite interval of the vevs of φ. In the landscape, at very high scales where the influence of the potential is negligible, the initial value of φ may be anything, and so there will be many regions where φ ∼ O(M P l ).…”

The dilaton potential from

“…In particular, the cosmological constant does not have to be small at the minimum after supersymmetry is broken. Furthermore the cosmological problems emphasized in [19] about the dilaton field overrunning the nontrivial minimum towards the runaway one for generic initial conditions, may still hold in this case as well as the proposed ameliorations [27], similarly for the cosmological moduli problem [20].…”