Grand unification threshold effects in supersymmetric SU(5) models.

Abstract

We study low energy consequences of the heavy particle mass spectrum in two specific supersymmetric SU(5) models, the minimal model and the missing doublet model with natural doublet-triplet splitting. The grand unification threshold effects are found to be significant and strongly model dependent: The minimal model favors a high supersymmetry threshold (${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{SUSY}}$>1 TeV) for ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$(${\mathit{m}}_{\mathit{Z}}$${)}_{\mathrm{MS}\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}}$=0.113\ifmmode\pm\else\textpm\fi{}0.004 (MS\ifmmode\bar\else\textasciimacron\fi{} denotes the modified minimal subtraction scheme), whereas the missing doublet model favors a low threshold (${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{SUSY}}$9 TeV). The X-boson-mediated proton decay lifetime can be shortened by more than one order of magnitude in both models.