Nonsingular AdS-dS transitions in a landscape scenario

Understanding transitions between different vacua of a multiverse allowing eternal inflation is an open problem whose resolution is important to gain insights on the global structure of the spacetime as well as the problem of measure. In the classical theory, transitions from the anti-de Sitter to de Sitter vacua are forbidden due to the big-crunch singularity. In this paper, we consider toy landscape potentials: a double well and a triple well potential allowing anti-de Sitter and de Sitter vacua, in the effective dynamics of loop quantum cosmology for the k = -1 FRW model. We show that due to the nonperturbative quantum gravity effects as understood in loop quantum cosmology, nonsingular anti-de Sitter to de Sitter transitions are possible. In the future evolution, an anti-de Sitter bubble universe does not encounter a big-crunch singularity but undergoes a big bounce occurring at a scale determined by the underlying quantum geometry. These nonsingular transitions provide a mechanism through which a probe or a watcher, used to define a local measure, can safely evolve through the bounce and geodesics can be smoothly extended from anti-de Sitter to de Sitter vacua.