[论文解读] UV cut-off of the Standard Model and proton decays

Ryuichiro Kitano, Shohei Okawa|arXiv (Cornell University)|Jan 22, 2026

Particle physics theoretical and experimental studies被引用 0

一句话总结

作者提出一个框架，在能级 Lambda 约为 10^11 GeV 的紫外截断下，诱导具有与 SM Yukawa 相关的味结构的高维数目对称性违反算符，计算质子寿命，并显示与当前界限一致，同时预测 Hyper-Kamiokande 可能观测到的 p -> pi0 mu+ 衰变。

ABSTRACT

Non-observation of proton decays as well as the smallness of the neutrino masses can naturally be explained by the accidental baryon and lepton number symmetry in the Standard Model, where the approximate symmetries are a consequence of the absence of the baryon or lepton number violating operators at the renormalizable level. The neutrino masses at sub-eV scales can be explained by the presence of the dimension-five, $\ell\ell HH/Λ$, term in the Lagrangian, suggesting that a more fundamental theory takes over beyond the energy scale $Λ$. We consider the possibility that the theory above the scale $Λ$ generates general higher dimensional operators with the flavor structure implied by the Yukawa interactions in the Standard Model. Such a set-up can be realized, for example, in the composite Higgs scenario with partial compositeness of fermions. The fermion masses and the neutrino masses are explained for $Λ\sim 10^{11}$GeV. The lifetime of proton in this scenario is, interestingly, consistent with the observed event of the $p o π^0 μ^+$ decay at the Super-Kamiokande experiment. The Hyper-Kamiokande experiments should see a large number of events soon after the data taking.

研究动机与目标

• Motivate a minimalist scenario where a UV cut-off scale Lambda governs higher-dimensional operators beyond the SM and explain fermion masses and neutrino masses.
• Impose an epsilon-based flavor structure on Yukawa couplings and BNV operators to predict proton decay patterns.
• Quantify proton lifetimes across decay channels as functions of Lambda, epsilon_q3, and lambda_yuk, and compare with current experimental limits.
• Identify the most promising proton decay modes for near-future detection (notably p -> pi0 mu+).

提出的方法

• Use SMEFT with dimension-six baryon-number-violating operators to induce proton decays.
• Parametrize flavor structure via epsilon factors tied to SM masses and mixings, following partial compositeness intuition.
• Run Wilson coefficients from Lambda to the weak scale using SMEFT RG equations and match to LEFT at the electroweak scale.
• Compute hadronic matrix elements via baryon chiral perturbation theory or lattice inputs to obtain nucleon-to-meson transition amplitudes.
• Derive analytical scaling of proton lifetimes with Lambda, epsilon_q3, and lambda_yuk, and evaluate decay rates for a complete set of channels.

Figure 1: The $\epsilon_{q_{3}}$ -dependence of the proton lifetime for each decay mode. The other free parameters are fixed at $\Lambda_{11}=1$ , $\lambda_{{\rm yuk}}=4\pi$ , and $c_{qqq\ell}=c_{qque}=c_{duue}=c_{duq\ell}=1$ .

实验结果

研究问题

• RQ1 What is the viable range of the UV cut-off scale Lambda that simultaneously explains fermion masses and neutrino masses and yields acceptable proton decay rates?
• RQ2 How does the flavor structure implied by Yukawa couplings (epsilon scheme) shape the dominant proton decay modes and lifetimes?
• RQ3 Can proton decay observables in this framework be reconciled with current Super-Kamiokande limits and be testable by Hyper-Kamiokande?
• RQ4 Which decay channels provide the strongest experimental reach given the proposed epsilon-based flavor ansatz?

主要发现

• Proton lifetimes are minimized for Lambda ~ 10^11 GeV (Λ11 ~ 1) under the epsilon scheme, while remaining consistent with current limits.
• All predicted proton decay rates lie within current Super-Kamiokande bounds for Λ ~ 10^11 GeV and ε_q3 in allowed ranges.
• The decay mode p -> π0 μ+ can be as short as ~10^34 years, potentially within reach of Hyper-Kamiokande.
• Leading decay modes into the second-generation leptons (e.g., p -> π0 μ+) are enhanced relative to first-generation channels due to the flavor structure.
• Analytical scaling shows Γ−1 ∝ Λ11^3 or Λ11^5 depending on the lepton chiral structure, and Γ−1 ∝ ε_q3^−2(n−m) with n,m counting quark/lepton fields in the operator.
• For Λ around 10^11 GeV, the framework remains compatible with existing limits while offering testable predictions for future experiments.