On superpotentials for D-branes in Gepner models

A large class of D-branes in Calabi-Yau spaces can be constructed at the Gepner points using the techniques of boundary conformal field theory. In this note we develop methods that allow to compute open string amplitudes for such D-branes. In particular, we present explicit formulas for the products of open string vertex operators of untwisted A-type branes. As an application we show that the boundary theories of the quintic associated with the special lagrangian submanifolds Im w(i)z(i) = 0 where w(i)(5) = 1 possess no continuous moduli.