Abstract: 
String theory suggests a unique and unambiguous augmentation of General Relativity, in which the entire closedstring massless NSNS sector is promoted to stringy graviton fields. O(D,D) Tduality then uniquely fixes the coupling of this 'Stringy Gravity' to other matter, leading to a generalization of Einstein's equations with an enhanced energymomentum tensor. In this talk I will explore the resulting cosmological implications and show that this yields an enriched framework beyond typical string cosmology, with solutions characterized by two equationofstate parameters (w,\lambda) rather than one (w). This includes a line in parameter space where GRlike solutions with constant dilaton are admitted for any w. However, neither an O(D,D)symmetric cosmological constant nor a scalar field with positive energy density gives rise to a de Sitter solution, suggesting that de Sitter may simply be an artefact of GR and belong to the swampland.
