CLASSICAL AND QUANTUM MASSIVE STRING

The classical and the quantum massive string model based on a modified BDHP action is analyzed in the range of dimensions 1 < d < 25. The di scussion concerning classical theory includes a formulation of the geo metrical variational principle, a phase-space description of the two-d imensional dynamics, and a detailed analysis of the target space geome try of classical solutions. The model is quantized using the ''old'' c ovariant method. In particular an appropriate construction of DDF oper ators is given and the no-ghost theorem is proved. For a critical valu e of one of the free parameters of the model the quantum theory acquir es an extra symmetry not present on the classical level, In this case the quantum model is equivalent to the non-critical Polyakov string an d to the old Fairlie-Chodos-Thorn massive string.