Survival of the Dirac points in rippled graphene
  We study the effects of the rippling of the graphene sheet on the quasiparticle dispersion. This is achieved using a generalization to the honeycomb lattice of the Momentum Average approximation, which is accurate for all coupling strengths and at all energies. We show that even though the position of the Dirac points may move and the Fermi speed can be renormalized significantly, quasiparticles with very long lifetimes survive near the Dirac points even for very strong couplings. 
Lucian Covaci and Mona Berciu