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The spectrum of glueballs in 2 +1 dimensions is calculated within an extended class of Isgur-Paton flux tube models and compared to lattice calculations of the low-lying SU(N≥2) glueball mass spectrum. Our modifications of the model include a string curvature term and a new way of dealing with the short-distance cutoff. We find that the generic model is remarkably successful at reproducing the positive charge conjugation, C = +, sector of the spectrum. The only large (and robust) discrepancy involves the 0-+ state, raising the interesting possibility that the lattice spin identification is mistaken and that this state is in fact 4-+. Additionally, the Isgur-Paton model does not incorporate any mechanism for splitting C= - from C=+ (in contrast with the case in 3 + 1 dimensions), while the "observed" spectrum does show a substantial splitting. We explore several modifications of the model in an attempt to incorporate this physics in a natural way. At the qualitative level we find that this constrains our choice to the picture in which the C= ± splitting is driven by mixing with new states built on closed loops of adjoint flux. However, a detailed numerical comparison suggests that a model incorporating an additional direct mixing between loops of opposite orientation is likely to work better, and that, in any case, a nonzero curvature term will be required. We also point out that a characteristic of any string model of glueballs is that the SU(N →∞) mass spectrum will consist of multiple towers of states that are scaled up copies of each other. To test this will require a lattice mass spectrum that extends to somewhat larger masses than currently available. © 2002 The American Physical Society

physical review. d. particles, fields, gravitation, and cosmology/physical review. d. particles and fields

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String models of glueballs and the spectrum ofSU(N)gauge theories in2+1dimensions