| his dissertation consists of a study of the following two problems related to the superfluidity in the boson systems in two dimensions.;The first problem is the supersymmetric quantum XY model. It is a modification of the quantum rotor model, whose ground state is exactly known. The model undergoes a vortex-binding transition from insulator to metal as the rotor coupling is varied. The three-site terms in the Hamiltonian are perturbatively unimportant, but they are relevant, i.e., they change the universality class of the phase transition from that of a (d + 1);The second problem is related to the momentum transfer between a superfluid... |
