The two-loop interaction correction coefficient to the universal ac conductivity of disorder-free intrinsic graphene is computed with the help of a field theoretic renormalization study using the BPHZ prescription. Non-standard Ward identities imply that divergent subgraphs (related to Fermi velocity renormalization) contribute to the renormalized optical conductivity. Proceeding either via density-density or via current-current correlation functions, a single well-defined value is obtained: $\mathcal{ C}= (19-6\pi)/12) = 0.01$ in agreement with the result first obtained by Mishchenko and which is compatible with experimental uncertainties.
Categories: cond-mat.mes-hall hep-ph hep-th