Phase Structure of Compact $QED_3$ with Massless Fermions

Abstract

In the framework of (2+1)-dimensional compact lattice QED with light fermions, we investigate the phase diagram in the $(β, N)$ plane. The approximations involved are related to an expansion of the effective fermionic action as a power series of the flavor number $N$. We also develop a new mechanism for understanding the $N-$critical phenomenon in the full theory. Our results for the specific heat indicate that only one phase does exist. We give strong evidences that this qualitative result should not be changed with the inclusion of higher order terms in the $N$ expansion.