From the string vacuum to FLRW or de Sitter via α' corrections

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 α' 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(ϕ). 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(ϕ) at moderate-coupling. We also identify a general mechanism for generating isotropic late-time attractors from a large basin of anisotropic initial conditions.

On the stability of string-hole gas

“…It follows a direct constraint on F and on the first derivative F ′ , with the last one completely fixed by the density of the gas. This seem to confirm the fact that the function F (H) should be non-analytic in the complex-H plane, as argued in [36] (see also [37]).…”

“…Moreover, as already mentioned in the Introduction, a natural extension of the model is the inclusion of a non-zero shear viscosity starting from anisotropic initial conditions. Furthermore, it would be very interesting to study the dynamical evolution of the SHG within the recent "hamiltonian" formalism described in [36,37]. We postpone those analysis to future works.…”

“…Hohm and Zwiebach adressed this issue by assuming that the O(d, d)-duality [3] holds to all orders, obtaining a simple and systematic action for the α ′ -corrections [16,29]. This duality-invariant action is a significant advancement in the context of string cosmology, allowing for a more consistent and robust description of the cosmological evolution [16,17,20,[28][29][30][31][32][33][34][35][36][37].…”