CURRENTS AND WARD-TAKAHASHI IDENTITIES FOR NONLOCAL QUANTUM-FIELD THEORIES

We consider a nonlocal quantum field theory, which can be used for the description of a composite particle, such as the nucleon interacting with its virtual pion field. Assuming a global symmetry of the theory, we discuss how to find the corresponding conserved currents. For the case of a U(1) symmetry, we then examine the conditions for second quantization and derive a general Ward-Takahashi identity. The formalism is then applied to the electromagnetic interaction.