Open bosonic string in massive background fields

The structure of renormalization is studied in the theory of open bosonic strings in background fields of various massive levels. The action functional that describes the interaction of a string with fields of the first massive level and the symmetries of this action functional are considered in detail. The renormalized trace operator is constructed for the energy-momentum tenser. The effective equations of motion of background fields are derived from the condition that this operator must vanish.