Worldsheet contributions to instantons in string effective field theories

The D-instantons in (p,p+1) theory can contribute to the string effective action. The relation with the D-instanton term in Type IIB string theory will be clarified. The equation of the scalar field is projected to the two-dimensional worldsheet, on which a (p,q) conformal field theory may be formulated. The energies of primary states in a minimal (p,p+1) theory coupled to a G(2) topological string are evaluated and compared with the particle spectrum.