From the string vacuum to FLRW or de Sitter via $\alpha'$ corrections

TL;DR

This paper refines a Hamiltonian approach to string cosmology equations, showing how adding a dilaton potential can lead to stable, late-time cosmologies like FLRW or de Sitter, starting from string vacua.

Contribution

It introduces a precise Hamiltonian formulation of $O(d,d)$-invariant string cosmology and demonstrates how non-perturbative potentials can produce realistic late-time universes.

Findings

Cosmological solutions can stabilize the dilaton at late times.

Solutions can evolve from string vacua to FLRW or de Sitter phases.

A mechanism for isotropic late-time attractors from anisotropic initial conditions.

Abstract

We first make more precise a recent "Hamiltonian" reformulation of the Hohm-Zwiebach approach to the tree-level, $O(d,d)$-invariant string cosmology equations at all orders in the $\alpha'$ expansion, and recall how it allows to give a simple characterization of a large class of cosmological scenarios connecting, through a non-singular bounce, two duality-related perturbative solutions at early and late times. We then discuss the effects of adding to the action a non-perturbative, $O(d,d)$-breaking, dilaton potential $V(\phi)$. The resulting cosmological solutions, assumed to approach at early times the perturbative string vacuum (with vanishing curvature and string coupling), can stabilize the dilaton at late times and simultaneously approach either a matter-dominated FLRW cosmology or a de-Sitter-like inflationary phase, depending on initial conditions and on the properties of $V(\phi)$ at moderate-coupling. We also identify a general mechanism for generating isotropic late-time attractors from a large basin of anisotropic initial conditions.