  The impact of the electron-electron Coulomb interaction on the optical
conductivity of graphene has led to a controversy that calls into question the
universality of collisionless transport in this and other Dirac materials.
Using a lattice calculation that avoids divergences present in previous nodal
Dirac approaches, our work settles this controversy and obtains results in
quantitative agreement with experiment over a wide frequency range. We also
demonstrate that dimensional regularization methods agree, as long as the
scaling properties of the conductivity and the regularization of the theory in
modified dimension are correctly implemented. Tight-binding lattice and nodal
Dirac theory calculations are shown to coincide at low energies even when the
non-zero size of the atomic orbital wave function is included, conclusively
demonstrating the universality of the optical conductivity of graphene.
