We study the $η$-$η'$ mixing up to next-to-next-to-leading-order in $U(3)$ chiral perturbation theory in the light of recent lattice simulations and phenomenological inputs. A general treatment for the $η$-$η'$ mixing at higher orders, with the higher-derivative, kinematic and mass mixing terms, is addressed. The connections between the four mixing parameters in the two-mixing-angle scheme and the low energy constants in the $U(3)$ chiral effective theory are provided both for the singlet-octet and the quark-flavor bases. The axial-vector decay constants of pion and kaon are studied in the same order and confronted with the lattice simulation data as well. The quark-mass dependences of $m_η$, $m_{η'}$ and $m_K$ are found to be well described at next-to-leading order. Nonetheless, in order to simultaneously describe the lattice data and phenomenological determinations for the properties of light pseudoscalars $π, K, η$ and $η'$, the next-to-next-to-leading order study is essential. Furthermore, the lattice and phenomenological inputs are well reproduced for reasonable values of low the energy constants, compatible with previous bibliography.
The ATLAS and CMS collaborations have recently released their new analyses of the diphoton searches. We look in detail the consequences of their results deriving strong constraints on models where a scalar resonance $s$ decays into two light pseudoscalars which in turn decay into two pairs of collimated photons, mis-identified with two real photons. In our construction, all mass terms are generated dynamically, and only one pair of vector-like fermions generate couplings which will be probed using the upcoming LHC data. Moreover, we show that a stable dark matter candidate, respecting the cosm…
Motivated by the recent diphoton excesses reported by both ATLAS and CMS collaborations, we suggest that a new heavy spinless particle is produced in gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which then decay to photons. The new resonances could arise from a new strongly interacting sector and couple to Standard Model gauge bosons only via the corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the consistency of the parameter space for those resonances.
Using the present upper bound on the neutron electric dipole moment, we give an estimate for the upper limit of the CP-violating couplings of the eta(eta') to the nucleon. Using this result, we then derive constraints on the CP-violating eta(eta')-pi-pi couplings, which define the two-pion CP-violating decays of the eta and eta' mesons. Our results are relevant for the running and planned measurements of rare decays of the eta and eta' mesons by the GlueX Collaboration at JLab and the LHCb Collaboration at CERN.
Light pseudoscalar eta and H->eta eta decay in the simplest little Higgs mode
SU（3）最简单的小希格斯模型在其原始框架中没有所谓的μ项，不可避免地涉及无质量的赝标玻色子η，这对b-物理和宇宙学轴子极限是有问题的。通过手工引入μ项，eta玻色子获得质量m_eta ~ μ，其在参数空间的大部分中可以轻于希格斯玻色子玻色子质量的一半。此外，引入的mu项产生相当大的H-η-η耦合。希格斯玻色子可以主要衰变为一对η，特别是当mH低于WW阈值时。对于高于Z+eta阈值的mH，H->Z+eta的另一个新的衰减通道可以是主导的或与H -> WW兼容。结果表明，由于新的H->eta-eta衰变通道以及H-Z-Z耦合的减弱，希格斯玻色子质量上的LEP束缚在一定程度上被放松.当f=3-4 TeV时，希格斯玻色子的质量束缚降到约110 GeV。由于eta玻色子主要衰变为bb对，因此H-> eta eta -> 4 b和H-> Z eta -> Z bb为在未来实验中寻找希格斯玻色子开辟了其他有趣的搜索通道。我们讨论这些问题。
The top-down holographic Witten-Sakai-Sugimoto model for low-energy QCD, augmented by finite quark masses, has recently been found to be able to reproduce the decay pattern of the scalar glueball candidate f0(1710) on a quantitative level. In this Letter we show that this model predicts a narrow pseudoscalar glueball heavier than the scalar glueball and with a very restricted decay pattern involving eta or eta' mesons. Production should be either in pairs or in association with eta(') mesons. We discuss the prospect of discovery in high-energy hadron collider experiments through central exclus…
Lightest pseudoscalar (P= pi^0, eta, eta') exchange contribution to the light-by-light (LbL) scattering piece of the muon anomaly, a_mu=(g_mu-2)/2, has been evaluated using a resonance chiral Lagrangian (RχL). Best description of pion transition form-factor (TFF) data is obtained with only tiny violations of one of the relations in the minimal consistent set of short-distance constraints on the anomalous RχL couplings. eta^{(')} TFF, predicted in terms of the pi TFF and the eta-eta^' mixing, are in good agreement with measurements. With this input, we obtain a_mu^{P,LbL} = (10.47\pm0.54)x10^-1…
The evaluation of the numerically dominant pseudoscalar-pole contribution to hadronic light-by-light scattering in the muon g-2 involves the pseudoscalar-photon transition form factor F_{P gamma^* gamma^*}(-Q_1^2, -Q_2^2) with P = pi^0, eta, eta^\prime and, in general, two off-shell photons with spacelike momenta Q_{1,2}^2. We show, in a largely model-independent way, that for pi^0 (eta, eta^\prime) the region of photon momenta below about 1 (1.5) GeV gives the main contribution to hadronic light-by-light scattering. We then discuss how the precision of current and future measurements of the s…
We derive the pseudoscalar condensate induced by anomaly and vorticity from the Wigner function for massive fermions in homogeneous electromagnetic fields. It has an anomaly term and a force-vorticity coupling term. As a mass effect, the pseudoscalar condensate is linearly proportional to the fermion mass in small mass expansion. By a generalization to two-flavor and three-flavor cases, the neutral pion and eta meson condensates are calculated from the Wigner function and have anomaly parts as well as force-vorticity parts, in which the anomaly part of the neutral pion condensate is consistent…
Elastic and inelastic SU(3)-breaking final-state interactions in B decays to pseudoscalar mesons
我们讨论了满足Zweig规则的SU（3）破缺末态相互作用（FSI）在B-> PP衰变中的所有贡献（忽略粲化中间态），其中PP = pi pi，pi K，KK，pi eta（eta'），K eta（eta'）.首先，研究了SU（3）破缺对Pomeron交换再散射的影响。然后，在对非Pomeron FSI中SU（3）破缺的模式做了一个合理的假设之后，我们给出了后者如何修改短距离振幅的一般公式。在SU（3）极限下，这些公式依赖于表征所有非坡密子再散射效应强度的三个有效参数。我们指出，B-> K ^+ K ^-分支比的实验界限可能只限制了其中一个FSI参数的值。因此，B-> K ^+ K ^-衰变率的小并不意味着其他衰变中的再散射效应可以忽略不计。假设该参数的值为零，我们对可用的B-> PP分支比执行各种拟合。拟合确定了夸克图SD振幅、剩余的两个FSI参数和弱角γ。虽然所有B-> PP分支比的集合用其预期SM值周围的γ很好地描述，但是拟合也允许γ的其他值。对于几个这样的良好拟合，我们预测了B-> K pi、pi ^+ eta（eta '）、K ^+ eta（eta'）衰变的不对称性，以及B ^0（t）-> pi ^+ pi ^-的时间依赖速率的CP破坏参数S_{pi pi}和C_{pi pi}的值。除了最近的B ^+-> pi ^+ eta不对称性测量存在问题之外，与数据的比较似乎有利于符…
