The neutral Higgs phenomena for the Hubbard hamiltonian

Using a functional integral method the authors show that the Hubbard model coupled weakly in the third dimension is equivalent to an XY model (the phase fluctuation of the charge singlets) coupled to a neutral Higgs field induced by the spinon fluctuations. The analysis is performed for the non half-filled band case. The critical behavior is similar to the three dimensional type II superconductor