An effective string theory of vortex ring excitations in a boson superfluid can in principle be derived using the coherent-state functional integral. The details of this derivation are complicated but lead unambiguously to the existence of a purely imaginary term in the string's effective action. This term is responsible for stabilizing a microscopic vortex ring against collapse if its momentum is sufficiently great. © 1992.

THE magnetic susceptibility of C60 and the possibility of magnetic-field-induced π-electron ring currents in this carbon spheroid have been of interest since the initial experiments on carbon clusters1. If the molecule is regarded as a sphere with a radius of 3.5 Å, on which 60 electrons are free to move, the Pauling ring-current model predicts a ring-current diamagnetic susceptibility 41 times the π-electron ring-current magnetic susceptibility of benzene with the field normal to the plane of the six-membered ring2,3.

In a previous publication we conclude that: "Although planar aromatic hydrocarbons and graphite have provided appropriate points of analogy for the π-electron energy structure of C60, it is clear that the magnetic response of C60 is unlike that of any other molecule yet encountered". In a recent Letter, Fowler, Lazzeretti and Zanasi (FLZ), report ab initio calculations on the magnetic susceptibility of icosahedral C60. FLZ conclude that C60 possesses "... the strong diamagnetism expected of an aromatic system".