The method of uniqueness and the optical conductivity of graphene: New application of a powerful technique for multiloop calculations

We briefly review the uniqueness method, which is a powerful technique for calculating multiloop Feynman diagrams in theories with conformal symmetries. We use the method in the momentum space and show its effectiveness in calculating a two-loop massless propagator Feynman diagram with a noninteger index on the central line. We use the obtained result to compute the optical conductivity of graphene at the infrared Lorentz-invariant fixed point. We analyze the effect of counterterms and compare with the nonrelativistic limit.