SPONTANEOUS SYMMETRY-BREAKING OF (1+1)-DIMENSIONAL PHI(4) THEORY IN LIGHT-FRONT FIELD-THEORY

We study spontaneous symmetry breaking in (1+1)-dimensional phi4 theory using the light-front formulation of field theory. Since the physical vacuum is always the same as the perturbative vacuum in light-front field theory the fields must develop a vacuum expectation value through the zero-mode components of the field. We solve the nonlinear operator equation for the zero mode in the one-mode approximation. We find that spontaneous symmetry breaking occurs at lambda(critical) = 4pi (3 + square-root 3) mu2, which is consistent with the value lambda(critical) = 54.27 mu2 obtained in the equal-time theory. We calculate the vacuum expectation value as a function of the coupling constant in the broken phase both numerically and analytically using the delta expansion. We find two equivalent broken phases. Finally we show that the energy levels of the system have the expected behavior for the broken phase.