We examine the phase structure of the two-flavor Schwinger model as a
function of the θ-angle and the two masses, m1 and m2. In
particular, we find interesting effects at θ=π: along the
SU(2)-invariant line m1=m2=m, in the regime where m is much smaller
than the charge g, the theory undergoes logarithmic RG flow of the
Berezinskii-Kosterlitz-Thouless type. As a result, in this regime there is a
non-perturbatively small mass gap ∼e−Ag2/m2. The SU(2)-invariant
line lies within a region of the phase diagram where the charge conjugation
symmetry is spontaneously broken and whose boundaries we determine numerically.
Our numerical results are obtained using the Hamiltonian lattice gauge
formulation that includes the mass shift mlat=m−g2a/4 dictated
by the discrete chiral symmetry.Comment: 7 pages, 3 figures; v2 minor improvements, refs adde