Strong-coupling calculations of lattice gauge theories: (1 + 1)-dimensional exercises

Strong-coupling methods for solving gauge theories formulated on a lattice are illustrated by studying the lattice version of the massive Schwinger model. The vacuum state of the model spontaneously breaks chiral symmetry and is equivalent to an Ising antiferromagnetic chain. Several lattice perturbation-theory calculations are carried out to fourth order in the dimensionless expansion parameter $\frac{1}{g^2{a}^2}$, where $a$ is the lattice spacing. Padé approximants are then employed to extrapolate the calculations to large $\frac{1}{g^2{a}^2}$. Good agreement between these calculations and exact results on the continuum massive Schwinger model are found.