  In a recent paper we showed how Starobinsky-like inflation could emerge from
dilaton dynamics in brane cosmology scenarios based on string theory, in which
our universe is represented as a three-brane and the effective potential
acquires a constant term from a density of effectively point-like
non-perturbative defects on the brane: "D-particles". Here we explore how
quantum fluctuations of the ensemble of D-particles during the inflationary
period may modify the effective inflationary potential due to the dilaton. We
then discuss two specific ways in which an enhanced ratio of tensor to scalar
perturbations may arise: via either a condensate of vector fields with a
Born-Infeld action that may be due to such recoil fluctuations, or graviton
production in the D-particle vacuum.
