Abstract:
Motivated by a puzzle in the study of two dimensional lattice Quantum Electrodynamics with staggered fermions, we construct a two dimensional fermionic model with a global $U(1)$ symmetry. Our model can be mapped into a model of closed packed dimers and plaquettes. Although the model has the same symmetries as the $XY$ model, we show numerically that the model lacks the well known Kosterlitz-Thouless (KT) phase transition. The model is always in the gapless phase showing the absence of a phase with vortex condensation. In other words the low energy physics is described by a non-compact $U(1)$ field theory. We show that by introducing an even number of layers one can introduce vortex condensation within the model and thus also induce a KT transition.