  We compute the Coulomb correction $\mathcal{C}$ to the a. c. conductivity of
interacting massless Dirac particles in graphene in the collisionless limit
using the polarization tensor approach in a regularization independent
framework. Arbitrary parameters stemming from differences between
logarithmically divergent integrals are fixed on physical grounds exploiting
only spatial $O(2)$ rotational invariance of the model which amounts to
transversality of the polarization tensor. Consequently $\mathcal{C}$ is
unequivocally determined to be $(19- 6\pi)/12$ within this effective model. We
compare our result with explicit regularizations and discuss the origin of
others results for $\mathcal{C}$ found in the literature.
