Cosmology at the top of the alpha ' tower

The cosmology of the fully alpha ' -corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in alpha '. We comment on how an infinite tower of alpha ' corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of alpha ' corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.
QC 20220615Nordita SU