Abstract

There are many compactifications of string theory and, consequently, there is a large set of four-dimensional effective theories arising in its low-energy limits. Can cosmology guide the search for observationally viable vacua? I will review how vacua that are consistent with the observation of an accelerated expansion can be expected to be very rare in ‘random’ supergravity theories without additional structures, and how this may be used to find corners of the ‘landscape’ with more favourable properties. I will show that in some regions of the moduli space, general flux compactifications of type IIB string theory and F-theory exhibit universal spectra that are independent of the geometry, topology or flux threading the compactification manifold. Moreover, these spectra are in stark contrast with the expectations from random ensembles of supergravity theories. Finally, I will show how de Sitter vacua appear with comparatively little tuning by spontaneous supersymmetry breaking in compactifications with a weakly broken “no-scale” symmetry.