Neutrino Masses Induced by R-Parity Violation in a SUSY SU(5) Model with Additional bar{5}'_L+5'_L

Within the framework of an SU(5) SUSY GUT model, a possible general form of the neutrino mass matrix induced by R-parity violation is investigated. The model has matter fields \bar{5}'_{L}+5'_{L} in addition to the ordinary matter fields \bar{5}_{L}+10_{L} and Higgs fields H_u+\bar{H}_d. The R-parity violating terms are given by \bar{5}_{L} \bar{5}_{L} 10_{L}, while the Yukawa interactions are given by \bar{H}_d \bar{5}'_{L} 10_{L}. Since the matter fields \bar{5}'_L and \bar{5}_L are different from each other at the unification scale, the R-parity violation effects at a low energy scale appear only through the \bar{5}'_L \leftrightarrow \bar{5}_{L} mixings. In order to make this R-parity violation effect harmless for proton decay, a discrete symmetry Z_3 and a triplet-doublet splitting mechanism analogous to that in the 5-plet Higgs fields are assumed.