We study baryon-number-violating processes, including proton and bound neutron decays and $n-\bar n$ oscillations, in a left-right-symmetric (LRS) model in which quarks and leptons have localized wavefunctions in extra dimensions. In this model we show that, while one can easily suppress baryon-number-violating nucleon decays well below experimental bounds, this does not suppress $n-\bar n$ transitions, which may occur at levels comparable to current limits. This is qualitatively similar to what was found in an extra-dimensional model with a Standard-Model low-energy effective field theory (SMEFT). We show that experimental data imply a lower limit on the mass scale $M_{n \bar n}$ characterizing the physics responsible for $n-\bar n$ oscillations in the LRS model that is significantly higher than in the extra-dimensional model using a SMEFT and explain the reason for this. Our results provide further motivation for new experiments to search for $n - \bar n$ oscillations.
Testing axial and electromagnetic nucleon form factors in time-like regions in the processes $\bar p + n\to π^- +\ell^-+\ell^+$ and $\bar p+ p\to π^0 +\ell^- + \ell^+$, $\ell=e$, $μ$
New possibility for further measurements of nucleon form factors at large momentum transfer in time-like region: $\bar{p}+{p}\to \ell^+ +\ell^-$, $\ell=e$ or $μ$
We study the helicity distributions of light flavor quark-antiquark ($q \bar{q}$) pairs in the nucleon sea. The valence quarks are handled by adopting the light-cone SU(6) quark-spectator-diquark model and the sea $q \bar{q}$ pairs are treated from statistical consideration by introducing the helicity suppression factors $l_q(x)$ and $\bar l_q(x)$ to parametrize the helicity distributions of q-flavor sea quark and antiquark respectively, while $Δl_q(x)=l_q(x)-\bar l_q(x)$ represents a combined effect of helicity contribution due to sea $q \bar{q}$ pairs. From fitting the nucleon polarization a…
It is known that limits on baryon-violating nucleon decays do not, in general, imply corresponding suppression of $n - \bar n$ transitions. In the context of a model with fermions propagating in higher dimensions, we investigate a related question, namely the implications of limits on $ΔL=-1$ proton and bound neutron decays mediated by four-fermion operators for rates of nucleon decays mediated by $k$-fermion operators with $k =6$ and $k=8$. These include a variety of nucleon and dinucleon decays to dilepton and trilepton final states with $ΔL=-3, \ -2, \ 1$, and $2$. We carry out a low-energy…
Baryon-number-violating nucleon decays in SMEFT extended with a light scalar
State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础研究中心物质结构与基本相互作用卓越中心广东省核科学重点实验室）；Sydney Consortium for Particle Physics and Cosmology, School of Physics, The University of New South Wales（新南威尔士大学物理学院悉尼粒子物理与宇宙学联盟）
Dielectron production in reactions $π^- p \rightarrow n e^+e^-$ and $π^- p \rightarrow n e^+e^- γ$ at energies less than 1 GeV is studied assuming electron-positron pair production to occur in the virtual time-like photon splitting process. Theoretical predictions of the effective mass distribution of dielectrons and their angular dependence are presented. Extraction of the electromagnetic form factor of baryon transition in the time-like region from future experiments of the HADES Collaboration is discussed.
We have previously calculated the pion-nucleon $Σ_{πN}$ term in the chiral mixing approach with $u,d$ flavors only, and found the lower bound $Σ_{πN} \geq \left(1 + \frac{16}{3} \sin^2 θ\right){3 \over 2} \left(m_{u}^{0} + m_{d}^{0}\right)$. The mixing angle $θ$ can be calculated as $\sin^2θ= \frac{3}{8}\left(g_A^{(0)} + g_A^{(3)}\right)$. With presently accepted values of current quark masses, this leads to $Σ_{πN} \geq 58.0 \pm 4.5 \begin{array}{l} +11.4 \\ -6.5 \end{array}$ MeV, which is in agreement with the values extracted from experiments, and substantially higher than most previous two…
Dark matter that participates in baryon-number violating interactions can annihilate with baryons if the dark matter particle is not protected under discrete symmetries. In this paper we investigate the dark matter - baryon annihilation in color-triplet extensions of the Standard Model, in which a fermionic dark matter can be kinematically stable within a small mass range near the proton mass. We demonstrate that the DM's annihilation with nucleons can be probed to stringent limits at large-volume water Cherenkov detectors like the Super-Kamionkonde experiment, with the mediator scale $m_Φ$ co…
Intrinsic charm content of the nucleon and charmness-nucleon sigma term
在推广的手征组分夸克模型中，研究了核子的内禀$c \bar{c}$含量。将核子看作是三夸克和五夸克的混合物，相应的跃迁用$^{3}$ P \it机制处理，计算了核子波函数中夸克-反夸克分量的几率.给出了在核子波函数和粲-核子σ项中的$c \bar{c}$几率的预言。我们的数值计算结果与文献中报道的各种其他方法的预测是一致的。
Intrinsic strange distributions in the nucleon from the light-cone models
对核子中奇异夸克和反奇异夸克分布的精确认识是更好地理解强相互作用和核子结构的重要一步。此外，核子中的$ s-\bar s $不对称性在一些涉及强子的物理过程中起着重要的作用。本文的目的是研究核子奇异海的内禀奇异贡献。为此，我们计算了各种光锥模型，包括BHPS，标量五夸克模型和介子-重子模型的内禀奇异分布，并比较了它们的结果。这些模型可以导致在不同的$ x $值中占主导地位的内禀奇异的相当不同的分布。此外，介子-重子模型导致的$ s-\bar s $不对称性，可以在某些情况下从PDF的整体分析获得的结果进行比较。我们还提出了一个简单的参数化为每个模型预测的内在奇怪的分布。
Two different approaches to mass and structure of the nucleon are discussed in recent works, ${\it viz.}$ (case 1) the QCD lagrangian evaluated via lattice calculations and (case ii) spontaneous symmetry breaking mediated by the $σ$ field. These approaches are complementary in the sense that the QCD lagrangian makes use of the gluon content of the nucleon entering in terms of the gluon trace-anomaly and ignores the effects of $q{\bar q}$ vacuum polarization, whereas in spontaneous symmetry breaking masses are formed by attaching $q{\bar q}$ pairs to the valence quarks, thus giving them a defin…
