Stabilizing the Dilaton in Superstring Cosmology

TL;DR

The paper analyzes dilaton stabilization in superstring cosmology by leveraging scaling solutions for exponential potentials. It shows that a background barotropic fluid can induce quasi-scaling regimes in which the dilaton evolves toward a minimum, even when the potential is steep. Applied to racetrack (two-condensate) and one-condensate with nonperturbative K"ahler corrections models, the authors derive analytic scaling estimates and demonstrate that stabilization occurs for a wide range of initial conditions, with the minimum characterized by an approximately fixed $N_{\min}$ and $H_{\min}$ set by low-energy requirements. This work suggests that dilaton stabilization is more generic than previously thought and has significant implications for moduli problems and low-energy SUSY phenomenology, including the gravitino-dilaton mass hierarchy.

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 quasi scaling 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.

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