A new source for a braneworld cosmological constant from a modified   gravity model in the bulk
  We show that a four-dimensional equation of state for a cosmological constant term arises from a perfect fluid in the bulk in the context of a gravity model where the scalar curvature is non-minimally coupled to the perfect fluid Lagrangian density. The four-dimensional theory is fully determined from the induced equations on the brane, subject to the boundary conditions derived across the brane. 
Orfeu Bertolami, Carla Carvalho and Joao Laia