LAGRANGIAN BRST QUANTIZATION AND UNITARITY

An effective action for gauge theories of general form is constructed in the framework of the Lagrangian approach on the basis of the unitarity condition for the S matrix. Necessary conditions for the existence of a unitary S matrix are formulated. An explicit expression for the effective action is obtained for a large class of physically interesting theories, including Yang-Mills fields, an antisymmetric tensor field, and string field theory.