On the Correspondence between the Strongly Coupled 2-Flavor Lattice Schwinger Model and the Heisenberg Antiferromagnetic Chain.

We study the strong coupling limit of the 2-flavor massless Schwinger model on a lattice using staggered fermions and the Hamiltonian approach to lattice gauge theories. Using the correspondence between the low-lying states of the 2-flavor strongly coupled lattice Schwinger model and the antiferromagnetic Heisenberg chain established in a previous paper, we explicitly compute the mass spectrum of this lattice gauge model: we identify the low-lying excitations of the Schwinger model with those of the Heisenberg model and compute the mass gaps of other excitations in terms of vacuum expectation values (v.e.v.'s) of powers of the Heisenberg Hamiltonian and spin–spin correlation functions. We find a satisfactory agreement with the results of the continuum theory already at the second order in the strong coupling expansion. We show that the pattern of symmetry breaking of the continuum theory is well reproduced by the lattice theory; we see indeed that in the lattice theory the isoscalar 〈ψψ〉 and isovector 〈ψσaψ〉 chiral condensates are zero to every order in the strong coupling expansion. In addition, we find that the chiral condensate 〈ψ(2)Lψ(1)Lψ(1)Rψ(2)R〉 is nonzero also on the lattice; this is the relic in this lattice model of the axial anomaly in the continuum theory. We compute the v.e.v.'s of the spin–spin correlators of the Heisenberg model which are pertinent to the calculation of the mass spcetrum and we obtain an explicit construction of the lowest lying states for finite size Heisenberg antiferromagnetic chains.