IR Inflation from Multiple Branes

In this paper we examine the IR inflation scenario using the DBI action, where we have N multiple branes located near the tip of a warped geometry. At large N the solutions are similar in form to the more traditional single brane models, however we find that it is difficult to simultaneously satisfy the WMAP bounds on the scalar amplitude and the scalar spectral index. We go on to examine two new solutions where N = 2 and N = 3 respectively, which both have highly non-linear actions. The sound speed in both cases is dramatically different from previous works, and for the N = 3 case it can actually be zero. We show that inflation is possible in both frameworks, and find that the scalar spectral index is bounded from above by unity. The level of non-gaussian fluctuations are smaller in the N = 2 case compared to the single brane models, whilst those in the N = 3 case are much larger.