CANONICAL APPROACH TO STRING THEORY IN MASSIVE BACKGROUND FIELDS

A method of constructing a canonical gauge-invariant quantum formulati on for a non-gauge classical theory depending on a set of parameters i s advanced and then applied to the theory of a closed bosonic string i nteracting with massive background fields. Choosing an ordering prescr iption and developing a suitable regularization technique, we calculat e quantum gauge algebra up to linear order in background fields. The r equirement of closure for the algebra leads to equations of motion for the massive background fields, which appear to be consistent with the structure of the string spectrum.