Excited glue and the vibrating flux tube
  Recent lattice results for the energy of gluonic excitations as a function of quark separation are shown to correspond to transverse relativistic flux tube vibration modes. For large quark separations all states appear to degenerate into a few categories which are predicted uniquely, given the ground state. 
Theodore J. Allen, M. G. Olsson (U. Wisconsin), and Sinisa Veseli   (Fermilab)