Cosmological Constant in SUGRA Models Inspired by Degenerate Vacua
  It is well known that global symmetries protect local supersymmetry and a zero value for the cosmological constant in no--scale supergravity. A particular breakdown of these symmetries, which ensures the vanishing of the vacuum energy density, leads to the natural realisation of the multiple point principle (MPP). In the MPP inspired SUGRA models the cosmological constant is naturally tiny. 
C.D. Froggatt, R. Nevzorov, H.B. Nielsen