Phases of the Dirac determinant, Abelian Chern-Simons terms and Berry's   phases in the field theoretic description of graphene
  This talk presents a study of massless relativistic Dirac fields in three Euclidean dimensions, at finite temperature and density, in the presence of a uniform electromagnetic background. Apart from explaining the behavior of Hall's conductivity for graphene, our results show a direct relationship between the selection of a phase for the Dirac determinant and the generation (or lack thereof) of Berry's phases and Chern-Simons terms. 
E.M. Santangelo