Null geodesics in the Reissner-Nordstr\"om Anti-de Sitter black holes
  In this work we address the study of null geodesics in the background of Reissner-Nordstr\"om Anti de Sitter black holes. We compute the exact trajectories in terms of elliptic functions of Weierstrass, obtaining a detailed description of the orbits in terms of charge, mass and the cosmological constant. The trajectories of the photon are classified using the impact parameter. 
Norman Cruz, Marco Olivares, Joel Saavedra and J.R. Villanueva
gr-qc hep-th