We compute supersymmetric contributions to pion leptonic (π_{l2}) decays in the Minimal Supersymmetric Standard Model (MSSM). When R-parity is conserved, the largest contributions to the ratio R_{e/μ} = Γ[ π^+ \to e^+ ν_e(γ)]/Γ[ π^+ \to μ^+ ν_μ(γ)] arise from one-loop (V-A)x(V-A) corrections. These contributions can be potentially as large as the sensitivities of upcoming experiments; if measured, they would imply significant bounds on the chargino and slepton sectors complementary to current collider limits. We also analyze R-parity violating interactions, which may produce a detectable deviation in R_{e/μ} while remaining consistent with all other precision observables.
Supersymmetry without R-parity : Constraints from Leptonic Phenomenology
R-宇称守恒是超对称标准模型最流行的版本中的{ \it ad hoc}假设。大多数研究模型，允许R-奇偶违反已被限制到各种限制的情况下。本文所采用的单VEV参数化方法为无R宇称超对称性的唯象分析提供了一个可行的框架。我们在树水平上对轻子现象进行了全面的研究。对各种过程的实验约束进行了单独研究，然后结合产生的容许参数空间的区域。特别是，我们表明，大R-奇偶违反双线性耦合不排除，特别是对于大$\tanβ$。
Rare leptonic kaon and pion decays $K^+(π^+) \to μ^+\, ν_μ\, e^+ e^-$ can be used to probe a dark photon of mass ${\cal O}(10)$~MeV, with the background coming from the mediation of a virtual photon. This is most relevant for the 16.7-MeV dark photon proposed to explain a 6.8$σ$ anomaly recently observed in $^8$Be transitions by the Atomki Collaboration. We evaluate the reach of future experiments for different scenarios of how the dark photon couples with the standard model particles, and show that a great portion of the preferred 16.7-MeV dark photon parameter space can be decisively probed.…
Leptonic Radiative Decay in Supersymmetry without R parity
我们提出了一个详细的分析与精确的数值计算上的单圈贡献的辐射衰变的$μ$和$τ$，即$μ\to e γ$，$τ\to e γ$，和$τ\toμγ$从超对称没有R宇称的分支比，专注于贡献涉及双线性耦合。进行数值研究，以获得明确的界限下，目前的实验限制的参数。我们提出，并在计算中使用，精确的质量本征态有效耦合的公式。在这个意义上，我们提出了一个精确的分析，从近似的第一次。在将我们的结果与最接近的早期分析进行比较后，我们发现在某些${μ_i^*} {B_j}$组合上产生的约束存在重大差异。考虑了中微子质量对参数的约束。我们的结果表明，$μ\to e γ$上的分支比测量下降到$10^{-13}-10^{-14}$和超越，作为MEG实验的目标，有机会观察到从R-宇称违反情况的衰变。
Estimates for parameters and characteristics of the confining SU(3)-gluonic field in charged pions and kaons from leptonic decays and chiral symmetry breaking
In recent years, significant experimental indications that point towards Lepton Flavour Universality violating effects in B-decays, involving $b \to c τν$ and $b \to s \ell^+ \ell^-$ have been accumulated. A possible New Physics explanation can be sought within the framework of R-parity violating Supersymmetry, which contains the necessary ingredients to explain the anomalies via both leptoquark, tree-level exchange and one-loop diagrams involving purely leptonic interactions. In addition, an approximate $U(2)^2$ flavour symmetry, that respects gauge coupling unification, successfully controls…
We study the correlation between proton lifetime and leptonic CP violation in a class of renormalizable supersymmetric SO(10) grand unified theories (GUTs) with {\bf 10}, {\bf 126} and {\bf 120} Higgs fields, which provides a unified description of all fermion masses and possibly resolution of the strong CP problem. This specific model is unique in that it can readily be compatible with current proton lifetime limits for a supersymmetry (SUSY) breaking scale as low as 5 TeV due to the presence of a specific Yukawa texture. Our investigation here reveals that proton partial lifetimes predicted …
New measurements in leptonic kaon and pion decays: experimental and theoretical perspectives
Deutsches Elektronen-Synchrotron DESY（德国电子同步加速器）；Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering（霍里亚·胡卢贝伊核物理与核工程研发国家研究所）；INFN, Laboratori Nazionali di Frascati（意大利国家核物理研究院弗拉斯卡蒂国家实验室）；Institut für Physik, Humboldt-Universität zu Berlin（柏林洪堡大学物理研究所）
We present a determination of the ratio of kaon and pion leptonic decay constants in isosymmetric QCD (isoQCD), $f_K / f_π$, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with $N_f = 2 + 1 + 1$ flavors of Wilson-clover twisted-mass quarks, including configurations close to the physical point for all dynamical flavors. The simulations are carried out at three values of the lattice spacing ranging from $\sim 0.068$ to $\sim 0.092$ fm with linear lattice size up to $L \sim 5.5$~fm. The scale is set by the PDG value of the pion decay constant, $f_π^{i…
We investigate the leptonic decay constants of the pion and its excitations with a 5-d holographic model for quantum chromodynamics. We prove numerically that the leptonic decay constants of the excited states of the pion vanish in the chiral limit when chiral symmetry is dynamically broken. This nontrivial result is in agreement with a solid prediction of quantum chromodynamics and is based on a generalized Gell-Mann-Oakes-Renner relationship involving the decay constants and masses of the excited states of the pion. We also obtain an extended partially conserved axial-vector current relation…
Electromagnetic effects in the leptonic decay rates $π^+ \to μ^+ ν$ and $K^+ \to μ^+ ν$ are evaluated for the first time on the lattice. Following a method recently proposed in Ref. [1] the emission of virtual photons at leading order in the electromagnetic coupling is evaluated on the lattice and the infrared divergence computed for a point-like meson at finite lattice volume is subtracted. The physical decay rate is then obtained by adding the emission of real and virtual photons regularised with a photon mass. Using the gauge ensembles produced by the European Twisted Mass Collaboration wit…
With the recent completion of NNNLO results, the perturbative description of the $Υ$ system has reached a very high level of sophistication. We consider the non-perturbative corrections as an expansion in terms of local condensates, following the approach pioneered by Voloshin and Leutwyler. The leading order corrections up to dimension eight and the potential NLO corrections at dimension four are computed and given in analytical form. We then study the convergence of the expansion for the masses, the leptonic decay rates and the non-relativistic moments of the $Υ$ system. We demonstrate that …
We propose an supersymmetric explanation of the diphoton excess in the Minimal Supersymmetric Standard Model with the leptonic R-parity violation. Where the sneutrino serves as the 750 GeV resonance and produced through quark anti-quark annihilation. With introducing appropriate trilinear soft parameters, we show that the diphoton branching ratio is significantly enhanced compared with the conventional MSSM. The parameter space favored by diphoton excess strongly indicates the mass of smuon and stau fall into the range $375-410$ (375-480) GeV, which depending on the electroweakino masses. In a…
$|ΔI|=3/2$ non-leptonic hyperon decays in covariant baryon chiral perturbation theory
School of Physics, Beihang University（北京航空航天大学物理学院）；Department of Physics, Guangxi Normal University（广西师范大学物理系）；Guangxi Key Laboratory of Nuclear Physics and Technology, Guangxi Normal University（广西师范大学核物理与技术重点实验室）；Sino-French Carbon Neutrality Research Center, École Centrale de Pékin/School of General Engineering, Beihang University（北京航空航天大学中法碳中性研究中心/通用工程学院）；Peng Huanwu Collaborative Center for Research and Education, Beihang University（北京航空航天大学彭桓武教研中心）；Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences（中国科学院现代物理研究所南方核科学理论中心）
Comprehensive Analysis on Lepton Flavor Violating Higgs Boson to mu tau Decay in Supersymmetry without R Parity
在本文中，我们彻底研究了希格斯玻色子玻色子到穆陶衰变过程中涉及R宇称破坏耦合。通过全单圈图解计算，我们发现即使已知的实验约束，特别是严格的亚eV中微子质量边界，对某些R宇称破坏参数给出了严格的限制，在容许参数空间中，分支比仍然可以达到显著的值.因此，味违反轻子衰变是未来实验的兴趣。我们在这里介绍我们分析的主要结果。在此基础上，对h -> e μ和h -> e τ也作了一些讨论.
We extend the framework of QCD factorization to non-leptonic $B$ decays into three light mesons, taking as an example the decay $B^+ \to π^+ π^+ π^-$. We discuss the factorization properties of this decay in different regions of phase space. We argue that, in the limit of very large $b$-quark mass, the central region of the Dalitz plot can be described in terms of the $B \to π$ form factor and the $B$ and $π$ light-cone distribution amplitudes. The edges of the Dalitz plot, on the other hand, require different non-perturbative input: the $B \to ππ$ form factor and the two-pion distribution amp…
Many new physics scenarios predict the existence of the extra charged gauge boson $ W'$, which can induce the charged-current (CC) non-standard neutrino interactions (NSI). We investigate the constraints on the CC NSI in model-independent fashion via considering the $ W'$ contributions to the lepton flavor violating (LFV) decays $\ell_{i}\rightarrow \ell_{j}γ$, the pure leptonic flavor conservation (FC) decays $\ell_{i}\rightarrow \ell_{j}ν_{i}\bar{ν_{j}}$, leptonic decays of charged pion meson, semileptonic $τ$ decays, and superallowed $β$ decays. We find that the constraints on the pure lept…
We present a calculation of the leptonic decay-constant ratio $f_K/f_π$ in 2+1 flavor QCD. Our data set includes five lattice spacings and pion masses reaching down below the physical one. Special emphasis is placed on a careful study of all systematic uncertainties, especially the continuum extrapolation. Our result is perfectly compatible with the first-row unitarity constraint of the Standard Model.
