Optical properties of graphene: the Fermi liquid approach
  Optical properties of two-dimensional massless Dirac fermions are considered by the formalism of pseudospin precession equations which provides an easy and natural semiphenomenological way to include correlation effects. It is shown that the latter are negligible, with the only assumption that the system under consideration is normal Fermi liquid. This result probably explains recent experimental data on the universal optical conductivity of graphene (Nair R. R. et al, Science 320 (2008) 1308). 
M. I. Katsnelson