(Quasi-) de Sitter solutions across dimensions and the TCC bound

Abstract

In this work, we investigate the existence of string theory solutions with a d-dimensional (quasi-) de Sitter spacetime, for 3 ≤ d ≤ 10. Considering classical compactifications, we derive no-go theorems valid for general d. We use them to exclude (quasi-) de Sitter solutions for d ≥ 7. In addition, such solutions are found unlikely to exist in d = 6, 5. For each no-go theorem, we further compute the d-dependent parameter c of the swampland de Sitter conjecture, {M}_pfrac{mid nabla Vmid }{V}ge c . Remarkably, the TCC bound cge frac{2}{sqrt{left(d-1right)left(d-2right)}} is then perfectly satisfied for d ≥ 4, with several saturation cases. However, we observe a violation of this bound in d = 3. We finally comment on related proposals in the literature, on the swampland distance conjecture and its decay rate, and on the so-called accelerated expansion bound.