A Reexamination of Proton Decay in Supersymmetric Grand Unified Theories

TL;DR

This paper reexamines proton decay mechanisms in supersymmetric GUTs, highlighting how decay rates depend on parameters like anbeta and the dominance of specific operators, with implications for experimental predictions.

Contribution

It provides a detailed analysis of dimension-five proton decay operators in supersymmetric GUTs, clarifying their dependence on model parameters and identifying dominant decay channels.

Findings

Proton decay rates grow as anbeta^4 for large anbeta.

Branching ratios for specific decay modes can be precisely predicted.

Charged-lepton decay fractions vary significantly with model parameters.

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 $(u^cd_i^c)^\dagger(d_j\nu_\tau)$, induced by charged Higgsino dressing, completely dominate for moderate to large $\tanbeta$. The rate for $p \rarr (K^+,\pi^+) \bar{\nu}_\tau$ grows rapidly, as $\tanbeta^4$, and the K^+ to \pi^+ 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.