The physical state projection operator in dual resonance models for the critical dimension of space-time

The physical state projection operator for the simple dual resonance model in twenty-six dimensions of space-time and unit intercept in two forms (which are proved to be equivalent) is presented. One form obviously projects onto the so-called transverse states and the other obviously gives unity when inserted into any residue of a pole in a dual amplitude. Thus the authors explicitly verify the completeness of transverse states in 26 dimensions and have a weapon for constructing genuine unitary dual loop amplitudes (as shown in a second paper). They also present the corresponding results for the Neveu-Schwarz model. (11 refs).