R. W. Johnson and M. Teper, String models of glueballs and the spectrum of SU(N) gauge theories in 2+1 dimensions, Phys. Rev. D 66, 036006 (2002)

Abstract: 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.

DOI: https://doi.org/10.1103/PhysRevD.66.036006

arXiv: https://arxiv.org/abs/hep-ph/0012287