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Hyperon neutrinoless double beta decays in chiral perturbation theory

Zi-Ying Zhao, Ze-Rui Liang, Feng-Kun Guo, Li-Ping He, De-Liang Yao

TL;DR

This paper analyzes neutrinoless double beta decays of spin-1/2 hyperons within covariant baryon chiral perturbation theory at one loop, employing the dimension-5 Weinberg operator $L_{ΔL=2}$ as the lepton-number-violating source and the Majorana mass $m_{ββ}$. The authors derive the full one-loop hadronic amplitudes, decomposing the hadronic tensor $H_{μν}$ into 34 Lorentz structures with corresponding coefficients, and implement antisymmetrization required by identical leptons. They present Dalitz plots for six decay channels to illustrate the kinematic dependence of the decay amplitude, using standard CKM and weak constants, and note that certain diagrams vanish. A follow-up work will provide integrated observables such as differential decay rates and branching ratios, enabling comparisons with future experimental searches for LNV and insights into neutrino mass generation.

Abstract

We study the neutrinoless double beta decays of spin-1/2 hyperons, $B_1^- \to B_2^+ \ell^- \ell^-$ with $B_1^-\in \{Σ^-,Ξ^-\}$ and $B_2^+\in\{p,Σ^+\}$, which violate lepton number by two units. The decay amplitudes are computed within covariant baryon chiral perturbation theory at the one-loop level. Dalitz plots of the squared amplitude for six physical decay processes are presented in this proceeding, while a detailed numerical analysis will be presented in a forthcoming publication.

Hyperon neutrinoless double beta decays in chiral perturbation theory

TL;DR

This paper analyzes neutrinoless double beta decays of spin-1/2 hyperons within covariant baryon chiral perturbation theory at one loop, employing the dimension-5 Weinberg operator as the lepton-number-violating source and the Majorana mass . The authors derive the full one-loop hadronic amplitudes, decomposing the hadronic tensor into 34 Lorentz structures with corresponding coefficients, and implement antisymmetrization required by identical leptons. They present Dalitz plots for six decay channels to illustrate the kinematic dependence of the decay amplitude, using standard CKM and weak constants, and note that certain diagrams vanish. A follow-up work will provide integrated observables such as differential decay rates and branching ratios, enabling comparisons with future experimental searches for LNV and insights into neutrino mass generation.

Abstract

We study the neutrinoless double beta decays of spin-1/2 hyperons, with and , which violate lepton number by two units. The decay amplitudes are computed within covariant baryon chiral perturbation theory at the one-loop level. Dalitz plots of the squared amplitude for six physical decay processes are presented in this proceeding, while a detailed numerical analysis will be presented in a forthcoming publication.
Paper Structure (6 sections, 16 equations, 3 figures, 2 tables)

This paper contains 6 sections, 16 equations, 3 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Theoretical framework
  3. Chiral effective Lagrangian
  4. Decay amplitude
  5. Results
  6. Summary

Figures (3)

  • Figure 1: Illustration of the hyperon $0\nu\beta\beta$ decay, taking the $\Sigma^- \to p\ell^- \ell^-$ process with $\ell=e,\mu$ as an example.
  • Figure 2: One-loop Feynman diagrams contributing to the $0\nu \beta\beta$ decay of hyperons. The thick solid, thin solid and dashed lines represent baryons, leptons and pions. The gray box denotes the $\Delta L= 2$ vertices. The crossed diagrams are not shown explicitly.
  • Figure 3: Dalitz plots for the 6 hyperon $0\nu\beta\beta$ decay processes, illustrating the variation of the amplitude distribution across the kinematic region of $s$ and $u$. The color scale on the right corresponds to the logarithm of the amplitude modulus squared, i.e., $\log({|\mathcal{M}|^2}/{\langle m_{\beta\beta} \rangle^2})$.