Covariant Heisenberg picture of a relativistic positive-energy theory: The operator algebra of the rigid string

The covariant operator Heisenberg equations of motion and commutation relations following from positive-energy wave equations are obtained. The resulting theory is identical to that of a dual string model restricted to excitations of only the lowest normal modes. It is suggested that recent classical Dirac-bracket formulations of the full dual string are subject to reinterpretation, and are apparently Poincare covariant in four dimensions. The nucleus of the complete set of covariant quantum string relations is obtained from the restricted model, and it is shown that covariant normal-mode operators and those of the null plane cannot both have simple creation-operator character. (AIP)