New constraint on the minimal SUSY GUT model from proton decay

We present results of reanalysis on proton decay in the minimal SU(5) SUSY GUT model. Unlike previous analyses, we take into account a Higgsino dressing diagram of dimension 5 operator with right-handed matter fields ($RRRR$ operator). It is shown that this diagram gives a significant contribution for $p \to K^{+}\bar{\nu}_{\tau}$. Constraints on the colored Higgs mass $M_C$ and the sfermion mass $m_{\tilde{f}}$ from Super-Kamiokande limit become considerably stronger than those in the previous analyses: $M_C > 6.5\times 10^{16} \gev$ for $m_{\tilde{f}} < 1 \tev$. The minimal model with $m_{\tilde{f}} \lsim 2 \tev$ is excluded if we require the validity of this model up to the Planck scale.