On C-J and C-T in conformal QED

Abstract

QED with a large number N of massless fermionic degrees of freedom has a conformal phase in a range of space-time dimensions. We use a large N diagrammatic approach to calculate the leading corrections to C-T, the coefficient of the two- point function of the stress-energy tensor, and C-J, the coefficient of the two- point function of the global symmetry current. We present explicit formulae as a function of d and check them versus the expectations in 2 and 4 - epsilon dimensions. Using our results in higher even dimensions we find a concise formula for CT of the conformal Maxwell theory with higher derivative action F-mu nu (-V-2)F-d/2-2(mu nu). In d = 3, QED has a topological symmetry current, and we calculate the correction to its two- point function coefficient, C-J(top). We also show that some RG flows involving QED in d = 3 obey C-T(UV) > C-T(IR) and discuss possible implications of this inequality for the symmetry breaking at small values of N.