The ϵ-expansion for QED
Abstract
We study Quantum Electrodynamics in d=3 (QED3) coupled to Nf flavors of fermions. The theory flows to an IR fixed point for Nf larger than some critical number Ncf. For Nf≤Ncf, chiral symmetry breaking is believed to take place. In analogy with the Wilson-Fisher description of the critical O(N) models in d=3, we use the existence of a fixed point in d=4−2ϵ to study the three-dimensional theory. We show how the ϵ-expansion can be used to study the anomalous dimension of 2- and 4-fermion operators. The latter leads to an estimate of the critical number Ncf. An important novelty compared to the O(N) models is that, because of the structure of spinors, the theory in d=3 has an enhanced symmetry. We identify the operators in d=4−2ϵ that correspond to the additional conserved currents at d=3.
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