A Comment on Self-Tuning and Vanishing Cosmological Constant in the   Brane World
  In this note we elaborate on various five dimensional contributions to the effective 4D cosmological constant in brane systems. In solutions with vanishing 5D cosmological constant we describe a non-local mechanism of cancellation of vacuum energy between the brane and the singularities. We comment on a hidden fine tuning which is implied by this observation. 
Stefan Forste, Zygmunt Lalak, Stephane Lavignac and Hans Peter Nilles