$SU(5)\times SU(5)$ Unification, Seesaw Mechanism and R-Conservation
  A new supersymmetric grand unified model based on the gauge group $SU(5)\times SU(5)$ is discussed. The model has the feature that the conventional seesaw mechanism for neutrino masses is implemented using the $(15, 1)+(1,\bar{15)}$ representation. This multiplet may have a better chance of arising from level two compactification of superstring theories than the the ${bf \bar{126}}$ representation used in the SO(10) model. The model also naturally suppresses all R-parity violating interactions. 
R. N. Mohapatra