Small Cosmological Constants in String Theory

<!--HTML--><p>I will present a construction of vacua of string theory in which the magnitude of the cosmological constant is exponentially small.&nbsp;&nbsp;The vacua are supersymmetric AdS solutions in flux compactifications of type IIB string theory, with all moduli stabilized.&nbsp;&nbsp;The vacuum energy is small because we ensure the exact cancellation of all perturbative contributions, through an explicit choice of integer parameters determined by the topology and quantized fluxes.&nbsp;&nbsp;The nonperturbative contributions that remain are exponential in these integers.&nbsp;&nbsp;Finding cosmological constants of small magnitude in this landscape is exponentially easier than in Bousso-Polchinski landscapes, but extending our approach to positive cosmological constants in realistic universes is a difficult open problem.</p>