arXiv subjects

Wei-Qi Fan

Publications and source records attributed to Wei-Qi Fan.

4 recordsLinked to original sources

arXiv2026

Comprehensive investigation of nucleon decays into one lepton plus two mesons

We systematically investigate baryon number violating (BNV) nucleon decays into one lepton ($e,\mu,\nu/\bar\nu$) and two pseudoscalar mesons ($\pi\pi,\pi\eta,\pi K$) within the low-energy effective field theory (LEFT) framework. By employing chiral perturbation theory, we obtain general expressions for the decay widths of these three-body nucleon decay modes induced by dimension-6 LEFT BNV operators and express them in terms of the associated Wilson coefficients. Since the same set of LEFT operators contribute to the experimentally well-constrained two-body nucleon decays, we then utilize the experimental bounds on them to constrain the relevant Wilson coefficients. From the obtained constraints, we derive improved limits on the occurrence of 22 three-body modes involving a charged lepton and 9 modes containing a neutrino or an antineutrino, with the new partial lifetime bounds being orders of magnitude stronger than the existing experimental limits. Our framework and derived bounds will facilitate future experimental searches for these nucleon decays.

hep-ph↗

arXiv2026

Nucleon decays into one lepton plus two non-strange mesons

Nucleon decays into a lepton and two pseudoscalar mesons represent key channels for probing baryon number violation, complementing conventional two-body modes. In this Letter, we model-independently correlate two- and three-body processes within the framework of low-energy effective field theory, performing a global analysis that avoids single-operator-dominance assumption. We derive significantly improved bounds on 15 three-body modes with a lepton ($e^+,\,\mu^+,\hat\nu=\nu/\bar\nu$) and two non-strange mesons ($\pi,\eta$). For charged-lepton modes, our lower limits on partial lifetimes ($\Gamma^{-1}$) surpass current Particle Data Group (PDG) values by more than three orders of magnitude. For 5 (anti)neutrino modes, we establish for the first time $\Gamma^{-1}\gtrsim 10^{34}\,\rm yr$. Additionally, our analysis improves constraints on two-body processes $n\to e^+\pi^-$, $n\to \mu^+\pi^-$, and $p\to \hat\nu \pi^+$ by approximately a factor of 2 compared to the PDG limits. These results highlight the importance of leveraging correlations among different processes to better probe new physics, enabling more stringent constraints on experimentally challenging processes from well-measured ones.

hep-ph↗

arXiv2025

Comprehensive investigation on baryon number violating nucleon decays involving an axion-like particle

In this study, we systematically investigate baryon number violating (BNV) nucleon decays into an axion-like particle (ALP), within a low energy effective field theory extended with an ALP, which is referred to as aLEFT. Unlike previous studies in the literature, we consider contributions to nucleon decays from a complete set of dimension-eight BNV aLEFT operators involving light $u,\,d,$ and $s$ quarks. We perform the chiral irreducible representation (irrep) decomposition of these interactions under the QCD chiral group $\rm SU(3)_{\tt L}\times SU(3)_{\tt R}$, and match them onto the recently developed chiral framework to obtain nucleon-level effective interactions among the ALP, octet baryons, and octet pseudoscalar mesons. Within this framework, we derive general expressions for the decay widths of nucleon two- and three-body decays involving an ALP. Subsequently, we analyze momentum distributions for three-body modes and find that operators belonging to the newly identified chiral irreps $\pmb{6}_{\tt L(R)}\times \pmb{3}_{\tt R(L)}$ exhibit markedly different behavior compared to that in the usual irreps $\pmb{8}_{\tt L(R)}\times \pmb{1}_{\tt R(L)}$ and $\pmb{3}_{\tt L(R)}\times \bar{\pmb{3}}_{\tt R(L)}$. In addition, we reanalyze experimental data collected by Super-Kamiokande and establish bounds on the inverse decay widths of these new modes by properly accounting for experimental efficiencies and Cherenkov threshold effects because of the lack of direct constraints on those exotic decay modes. Our recasting constraints are several orders of magnitude more stringent than inclusive bounds used in the literature. Based on these improved bounds, we set conservative limits on associated effective scales across a broad range of ALP mass and predict stringent bounds on certain neutron and hyperon decays involving an ALP.

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arXiv2024

Baryon number violating hydrogen decay

Most studies on baryon number violating (BNV) processes in the literature focus on free or bound nucleons in nuclei, with limited attention given to the decay of bound atoms. Given that hydrogen is the most abundant atom in the universe, it is particularly intriguing to investigate the decay of hydrogen atom as a means to probe BNV interactions. In this study, for the first time, we employ a robust effective field theory (EFT) approach to estimate the decay widths of two-body decays of hydrogen atom into standard model particles, by utilizing the constraints on the EFT cutoff scale derived from conventional nucleon decay processes. We integrate low energy effective field theory (LEFT), chiral perturbation theory (ChPT), and standard model effective field theory (SMEFT) to formulate the decay widths in terms of the LEFT and SMEFT Wilson coefficients (WCs), respectively. By applying the bounds on the WCs from conventional nucleon decays, we provide a conservative estimate on hydrogen BNV decays. Our findings indicate that the bounds on the inverse partial widths of all dominant two-body decays exceed $10^{44}$ years. Among these modes, the least constrained diphoton decay $\Hy\to \gamma\gamma$ might be astrophysically interesting, although the monochromatic photon signal from our Sun is difficult to detect with current near-Earth telescopes.

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