A phenomenological comparison of conventional and supersymmetric guts

We compare the phenomenological predictions of grand unified theories (GUTs) and supersymmetric (susy) GUTs for nucleon decays, sin²θ_W and m_b/m_τ. Conventional GUTs are consistent with experiment for all three of these observables. In contrast with previous analyses, we find that susy GUTs have problems with sin²θ_W, but not with m_b/m_τ or the experimental lower limit on the nucleon lifetime. Susy GUTs may cause nucleon decays with an observable lifetime: in the simplest SU(5) susy GUT we find Γ(N→ν_τK) ≫ Γ(N→ν_μK) ≫ Γ(N→νπ, μ⁺K) ≫ Γ(N→μ⁺π) ≫ Γ(N→e⁺K) ≫ Γ(N→e⁺π).