In brane inflation, the relative brane position in the bulk of a brane world
is the inflaton. For branes moving in a compact manifold, the approximate
translational (or shift) symmetry is necessary to suppress the inflaton mass,
which then allows a slow-roll phase for enough inflation. Following recent
works, we discuss how inflation may be achieved in superstring theory. Imposing
the shift symmetry, we obtain the condition on the superpotential needed for
inflation and suggest how this condition may be naturally satisfied.Comment: 12 pages, 1 figure. Two references and few comments adde