Vanishing dimension five proton decay operators in the SU(5) SUSY GUT
  We propose a natural framework of   SU(5) supersymmetric grand unified theory with the minimal particle contents, which does not contain dimension five proton decay operators. The suitable fermion mass hierarchy can be reproduced by higher dimensional operators of an adjoint Higgs field which breaks   SU(5) gauge symmetry. 
Naoyuki Haba and Toshihiko Ota