Special Gravity/Cosmology/High Energy Theory Seminar

Despite impressive phenomenological successes, cosmological models are incomplete without an understanding of what happened at the big bang singularity. In this talk, based on work with T. Hertog and N. Turok (and following on the earlier seminar by Turok), I discuss a five-dimensional model cosmology with a big crunch singularity and ask whether time evolution can be consistently defined beyond this singularity, which would then be the big bang of an expanding universe. We use the AdS/CFT correspondence to map the problem to the study of a dual quantum field theory with a potential unbounded below, where the singularity corresponds to a field reaching infinity in finite time. The main idea is to use “self-adjoint extensions”, which amounts to putting boundary conditions at infinity in field space. Our results suggest that, at least in a certain parameter regime, a big crunch/big bang transition is the most likely outcome of cosmological evolution. We end with some speculations on the generation of nearly scale invariant cosmological perturbations.