NULL SPINNING STRINGS

We quantize in detail the closed string with vanishing tension, the null closed string. For Weyl ordering of quantum operators, the spectrum is continuous and there is no critical dimension. For normal ordering, however, the usual critical dimension holds and the spectrum is finite: the field content is the same as in the field theory (infinite tension) limit of usual (closed) strings. The content of bosonic null strings is massless gravity. We carry through the local supersymmetrization of this system and find similar conclusions, normal ordered null spinning strings contain in their spectrum only the massless supergravity multiplet. However, normal ordered bosonic null strings do not have a consistent quantum interpretation, whereas null spinning strings do. It points to the likely origin of some spontaneous symmetry breakdown which generates a non-zero tension, and an infinite tower of massive states. We also consider the hamiltonian formalism for quantum null (super)strings. © 1980.