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.

The generalized Bergshoeff-de Roo identification. Part II

“…• Our results can contribute to many recent works that study the role of T-duality for higher derivatives in the context of black-holes [67][68][69][70][71] and other solutions of cosmological relevance [65,66,[72][73][74][75][76][77][78].…”

Crisis on infinite earths: short-lived de Sitter vacua in the string theory landscape

“…In fact, as shown in [72,73], 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 [74], solutions to the equations of motion were studied in [75] and a model sourced by a string gas was introduced in [76]. This model has a short TCC compatible phase of accelerated (super-exponential) expansion that last long enough to solve the hori-JHEP04(2021)037 zon problem of standard cosmology [77], depicting the phenomenological relevance of this class of backgrounds.…”

Cosmology at the top of the α′ tower

“…Zwiebach [42,43] (generalizing [44]), who found the form of the most general action for the metric, the dilaton and the b-field when these fields only depend on time, which is invariant under O(d, d) transformations and which includes α corrections to all orders. The inclusion of coupling to other matter fields was then first explored in [45], and applications to string cosmology have been explored in a few studies so far [42,43,[45][46][47][48][49][50], often discovering new potential solutions, such as de Sitter-like or loitering backgrounds, which are otherwise often difficult to find in string cosmology (see, e.g., [51][52][53][54]). The current paper's aim is to go beyond these recent works on string-cosmology backgrounds to all orders in α .…”

“…To understand how different matter contents can allow for SEC violation and thus accelerated expansion in the Einstein frame, let us consider the set of solutions found in [47] of the form…”