Reheating a multi-throat universe by brane motion.pdfVIP

a r X i v : 0 7 0 6 .3 2 1 4 v 2 [ h e p - t h ] 3 J u l 2 0 0 7 UTAP-580, RESCEU-72/07 Reheating a multi-throat universe by brane motion Shinji Mukohyama Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033, Japan Abstract We propose a mechanism of reheating after inflation in multi-throat scenar- ios of warped extra dimensions. Validity of an effective field theory on the standard model (SM) brane requires that the position of the SM brane dur- ing inflation be different from the position long after inflation, i.e. the tip of the SM throat. After inflation, when the Hubble expansion rate becomes sufficiently low, the SM brane starts moving towards the tip and eventually oscillates. The SM fields are excited by the brane motion and the universe is reheated. We consider a U(1) gauge field on a wrapped D5-brane as a toy model to illustrate that fields confined to a brane are indeed excited by brane motion. Since interaction is suppressed only by the local string scale, the modulus corresponding to the brane position effectively decays into the SM fields. 1 Introduction Our universe appears to have many mass scales, including the Planck scale, the electroweak scale, the scale of inflation, the scale of cosmic expansion today, etc. One of the most outstanding problems in theoretical physics is, hence, to explain how hierarchies among those scales emerge in a natural way. The 5-dimensional braneworld scenario proposed by Randall and Sundrum gen- erates the large hierarchy between the Planck scale and the electroweak scale by a warped 5th dimension [1]. Although their original scenario does not recover the ordinary 4-dimensional Einstein gravity at low energy on the brane confining the standard model (SM) of particle physics, this flaw was fixed by inclusion of a moduli stabilization mechanism [2]. Moduli stabilization is important not only for the Randall-Sundrum scenario but also for any models with extra dim