Inflation from D3-brane motion in the background of D5-branes

We study inflation arising from the motion of a Bogomol'nyi-Prasad- Sommerfield D3-brane in the background of a stack of k parallel D5-branes. There are two scalar fields in this setup: (i) the radion field R, a real scalar field, and (ii) a complex tachyonic scalar field χ living on the world volume of the open string stretched between the D3 and D5 branes. We find that inflation is realized by the potential of the radion field, which satisfies observational constraints coming from the cosmic microwave background. After the radion becomes of the order of the string length scale ls, the dynamics is governed by the potential of the complex scalar field. Since this field has a standard kinematic term, reheating can be successfully realized by the mechanism of tachyonic preheating with spontaneous symmetry breaking.