$α'$-Cosmology: solutions and stability analysis

Abstract

We review O(d, d) Covariant String Cosmology to all orders in α in the presence of matter and study its solutions. We show that the perturbative analysis for a constant dilaton in the absence of a dilatonic charge does not lead to a time-independet equation of state. Meanwhile, the non-perturbative equations of motion allow de Sitter solutions in the String frame parametrized by the equation of state and the dilatonic charge. Among this set of solutions, we show that a cosmological constant equation of state implies a de Sitter solution both in String and Einstein frames while a winding equation of state implies a de Sitter solution in the former and a static phase in the latter. We also consider the stability of these solutions under homogeneous linear perturbations and show that they are not unstable, therefore defining viable cosmological scenarios.

Crisis on Infinite Earths: Short-lived de Sitter Vacua in the String Theory Landscape

“…In fact, as shown in [54,55], the entire tower of corrections is necessary for having dS solutions in the string frame (with zero fluxes and a time-dependent dilaton). After including matter in the form of a perfect fluid energy-momentum tensor in the framework [56], solutions to the equations of motion were studied in [57] and a model sourced by a string gas was introduced in [58]. This model has a short TCC compatible phase of accelerated (super-exponential) expansion that last long enough solve the horizon problem of standard cosmology [59], depicting the phenomenological relevance of this class of backgrounds.…”