A Reexamination of Proton Decay in Supersymmetric Grand Unified Theories

Abstract

We reconsider dimension-five proton decay operators, making semi-quantitative remarks which apply to a large class of supersymmetric GUTs in which the short-distance operators are correlated with the fermion Yukawa couplings. In these GUTs, which include minimal SU(5), the operators $(u^c{d}_i^c{)}^{†}(d_j{\nu }_{\tau })$, induced by charged Higgsino dressing, completely dominate for moderate to large $\tanbeta$. The rate for $p\to (K^{+},{\pi }^{+}){\bar{\nu }}_{\tau }$ grows rapidly, as $\tanbeta^4$, and the K^+ to π^+ branching ratio can often be precisely predicted. At small $\tanbeta$ the operators $(u{d}_i)(d_j\nu )$ are dominant, while the operators $(u{d}_i)(u{\ell }^{-})$, with left-handed charged leptons, are comparable to the neutrino operators in the generic GUT and suppressed in minimal GUTs. Charged-lepton branching fractions are always small at large $\tanbeta$. The electron to muon ratio is small in minimal GUTs but can be larger, even of order one, in other models. All other operators are very small. At small $\tanbeta$ in non-minimal GUTs, gluino and neutralino dressing effects on neutrino rates are not negligible.

10 pages, 3 figures, uses revtex