VACUUM STRUCTURES IN HAMILTONIAN LIGHT-FRONT DYNAMICS

Hamiltonian light-front dynamics of quantum fields may provide a usefu l approach to systematic nonperturbative approximations to quantum fie ld theories. We investigate inequivalent Hilbert-space representations of the light-front field algebra in which the stability group of the light front is implemented by unitary transformations. The Hilbert spa ce representation of states is generated by the operator algebra from the vacuum state. There is a large class of vacuum states besides the Fock vacuum which meet all the invariance requirements. The light-fron t Hamiltonian must annihilate the vacuum and have a positive spectrum. We exhibit relations of the Hamiltonian to the nontrivial vacuum stru cture.