Light-cone quantisation and manifestation of non-perturbative vacuum properties for scalar field theory

For a quantum field theory with interacting scalar fields treated in light-cone quantisation (LCQ) it is shown that the vacuum of the theory is always the perturbative vacuum. The fields can be split up into classical constant fields, determined by minima of the effective action, and quantum fields. The former ones replace the nontrivial vacuum expectation values of the conventionally quantised theory. When spontaneous symmetry breaking occurs, the classical fields are only determined up to symmetry transformations. This degeneracy corresponds to the degeneracy of the vacuum in the conventional approach. The effective actions of the conventional theory and LCQ are identical. Lightcone charges obey the canonical commutation relations with the fields and the canonical charge algebra relations. Ward identities and the appearance of Goldstone Bosons accompanying spontaneous symmetry breaking can be derived in analogy to the conventional case.