Ward identities in string theory

It is a pleasure and honor for me to participate in the celebration of the sixtieth birthday of Professor Miyazawa. This paper presents investigations of string theory in the BRS Hamiltonian formalism. The superstring theory is considered to be an attractive candidate for the unification of all fundamental forces. The requirement of gravitational, Yang-Mills and mixed anomalies cancellations imposes strong constraints on the choice of gauge groups. Furthermore, compactification of strings on specific tori has provided a mechanism to implement nonabelian gauge symmetries in the string theory which is an important ingredient in the construction of the heterotic string theory. It has been argued that various compactification schemes for the heterotic string expose different vacua of a single underlying theory