Dec. 9, 2014
Abstract: We propose a new approach for the calculation of the spectrum of excitations of QCD flux tubes. The method relies on approximate integrability of the low energy effective theory describing the flux tube excitations and is based on the Thermodynamic Bethe Ansatz (TBA). The approximate integrability is a consequence of the Lorentz symmetry of QCD. For excited states the convergence of the TBA technique is significantly better than that of the traditional perturbative approach.The improved theoretical control makes it manifest that existing lattice data provides strong evidence for a new pseudoscalar particle localized on the QCD fluxtube - the worldsheet axion.