Suppression of Proton Decay in the Missing-Partner Model for Supersymmetric SU(5) GUT

The Peccei-Quinn symmetric extension of the missing-partner model in the supersymmetric SU(5) grand unified model is consistent with the observed stability of the proton, even in the large $\tanβ$ region ($\simeq 50-60$) expected from the Yukawa unification. Moreover, the SU(5) gauge coupling constant remains small enough for the perturbative description of GUT's below the gravitational scale.