Exact renormalization group computation of the optical conductivity of graphene

The optical conductivity of a system of electrons on the honeycomb lattice interacting through a retarded electromagnetic field is computed by exact renormalization-group (RG) methods. By truncating the exact RG expression at one loop we find that the conductivity has the universal value π/2 times the conductivity quantum up to negligible corrections vanishing as a power law in the limit of low frequencies.