我们提出了一个计算的η/s的介子气体（零重子数），在unitarized NLO手征微扰理论计算的粘度，并确认观察到的η/s减少对可能的相变的夸克-胶子等离子体/液体。该值略高于以前在LO chi PT中估计的值。我们还研究了原子氩气的情况，以检查eta/s在一级相变中的不连续性。我们的研究结果表明，使用这个无量纲数，有时称为KSS数（与流体力学中的其他比率，如雷诺数或普朗特数类比），以确定相变和临界终点，在强相互作用的核物质之间的强子气体和夸克和胶子等离子体/液体的交叉。
英文摘要：
We present a calculation of eta/s for the meson gas (zero baryon number), with the viscosity computed within unitarized NLO chiral perturbation theory, and confirm the observation that eta/s decreases towards the possible phase transition to a quark-gluon plasma/liquid. The value is somewhat higher than previously estimated in LO chi PT. We also examine the case of atomic Argon gas to check the discontinuity of eta/s across a first order phase transition. Our results suggest employing this dimensionless number, sometimes called KSS number (in analogy with other ratios in fluid mechanics such as Reynolds number or Prandtl number) to pin down the phase transition and critical end point to a cross-over in strongly interacting nuclear matter between the hadron gas and quark and gluon plasma/liquid.
It has been realized for a long time that knowing the eta and eta^prime wave functions in terms of quark and gluon components probes our understanding of non-perturbative QCD dynamics. Great effort has been given to this challenge -- yet no clear picture has emerged even with the most recent KLOE data. We point out which measurements would be most helpful in arriving at a more definite conclusion. A better knowledge of these wave functions will significantly help to disentangle the weight of different decay subprocesses in semi-leptonic decays of D+, Ds^+ and B+ mesons. The resulting insights …
Determining weak phase gamma and probing new physics in b->s transitions from B->eta(eta')K
本文给出了由衰变B->ηK，η' K $ alone. Given a large ratio between color-suppressed and color-allowed tree diagrams extracted from global ππ(K) fits, γis determined from the current data of η' K and the result is in agreement with the global Standard Model(SM) fits. However, a smaller ratio from factorization based calculations gives $ γ \sim 90^ \circ $确定Cabibbo-Kobayashi-Maskawa矩阵中弱相γ的方法。如果在η^{（'）} K模中得到的γ与从其他模或其他方法得到的γ显著不同，则可以挑出SM之外的新物理。由η' K得到的γ的有效值对新的物理贡献非常敏感，可以用来提取一类对强相贡献不大的模型的新的物理参数。
The enhancement of the decay Upsilon(1D) -> eta Upsilon(1S) by the axial anomaly in QCD
结果表明，Uppersons（1^3D_1）-> eta Uppersons（1 S）和Uppersons（1^3D_2）-> eta Uppersons（1 S）的衰变率应与最近文献中讨论的Uppersons（1D）-> pi pi Uppersons（1 S）的衰变率相当，甚至可能超过。这种现象的原因是所讨论的eta跃迁被QCD中味单重态轴流反常的贡献所增强。
Transition form factors of pi^0, eta, eta' mesons are investigated by means of the anomaly sum rule -- an exact nonperturbative relation which follows from the dispersive representation of the axial anomaly. Considering the problem of contributions of operators originated from a non-(local) operator product expansion, we found that they are required by the available set of experimental data, including the most recent data from the Belle Collaboration (which, if taken alone, can be described without such contributions, although are compatible with them). In this approach we analyzed the experim…
我们研究了τ-> K π（eta，eta '）nu衰变的直接CP破坏.通过研究前向和后向不对称性，可以提取强子系统的L=0和L=1振幅的干涉。通过将标量和矢量介子引入手征拉格朗日量，计算了强子系统L=0和L=1角动量态对应的形状因子。我们包括实部和虚部的单圈修正的标量和矢量介子的自能。利用引入新的CP破坏相的双Higgs偶极子模型计算了前向和后向不对称的直接CP破坏。我们展示了前向和后向不对称的CP破坏如何依赖于新的CP破坏相和形状因子的强相。
In this talk it is reported on an analysis of the form factors for the transitions from a photon to one of the pseudoscalar mesons pi0, eta, eta', etac within the modified perturbative approach in which quark transverse degrees of freedom are retained. The report is focused on the discussion of the surprising features the new BaBar data exhibit, namely the sharp rise of the pi-gamma form factor with the photon virtuality and the strong breaking of flavor symmetry in the sector of pseudoscalar mesons.
We consider the chiral Lagrangian with a nonet of Goldstone bosons and a nonet of light vector mesons. The mixing between the pseudoscalar mesons eta and eta-prime is taken into account. A novel counting scheme is suggested that is based on hadrogenesis, which conjectures a mass gap in the meson spectrum of QCD in the limit of a large number of colors. Such a mass gap would justify to consider the vector mesons and the eta-prime meson as light degrees of freedom. The complete leading order Lagrangian is constructed and discussed. As a first application it is tested against electromagnetic tran…
The eta-photon transition form factor is evaluated in a formalism based on a phenomenological description at low values of the photon virtuality, and a QCD-based description at high photon virtualities, matching at a scale $Q_{0}^{2}$. The high photon virtuality description makes use of a Distribution Amplitude calculated in the Nambu-Jona-Lasinio model with Pauli-Villars regularization at the matching scale $Q_{0}^{2}$, and QCD evolution from $Q_{0}^{2}$ to higher values of $Q^{2}$. A good description of the available data is obtained. The analysis indicates that the recent data from the BaBa…
By means of the universal unitary and analytic model of electromagnetic structure of hadrons the two-photon decay rates of P=pi^0, eta, eta' mesons are determined in an alternative way from data on their transition form factors.
Soft gluon contributions to the B --> K eta' amplitude in a low energy bosonization model
有趣的B --> K eta'衰变提供了一个独特的机会来研究由企鹅b --> sG和b --> sGG跃迁产生的双胶子构型与eta'粒子固有的构型的结合。我们采用重-轻手征夸克模型作为计算工具，该模型以前曾应用于一个有点相关的B --> D eta'衰变，它考虑了非微扰软胶子对振幅的贡献。因此，我们得到了对单态企鹅振幅的新贡献，在我们的模型中，其占测量的B -> K eta'振幅的~ 10%。
In the framework of the QCD light-cone sum rules (LCSRs) we present the analysis of all $B, B_{s}\to η^{(\prime)}$ and $D, D_{s}\to η^{(\prime)}$ form factors ($f^+, f^0$ and $f^T$) by including $m_{η^{(\prime)}}^2$ corrections in the leading (up to the twist-four) and next-to-leading order (up to the twist-three) in QCD, and two-gluon contributions to the form factors at the leading twist. The SU(3)-flavour breaking corrections and the axial anomaly contributions to the distribution amplitudes are also consistently taken into account. The complete results for the $f^0$ and $f^T$ form factors …
In this thesis we discuss a rational and data-based description of the single- and double-virutal transition form factors of the lightest pseudoscalar mesons. We obtain an accurate description of these in the spacelike and low-energy timelike regions. The phenomenological applications are wide. Among them, we discuss, the eta-eta' mixing, the rare pseudoscalar decays into a lepton pair and the pseudoscalar-pole contribution to the hadronic light-by-light part of the anomalous magnetic moment of the muon. In all these cases we discuss and illustrate the relevance of employing a data-based appro…
The local-duality formulation of QCD sum rules allows for the prediction of hadronic form factors without knowledge of the subtle details of their structure. With the aid of this formalism, we take a fresh look at the behaviours of the charged-pion elastic form factor and of the form factors entering in the transitions of the ground-state neutral unflavoured pseudoscalar mesons pi^0, eta, eta' to one real and one virtual photon within a broad range of momentum transfers Q^2. The uncertainties induced by the approximations inherent to this local-duality approach are estimated by studying, in pa…
The production of pseudo scalar, Eeta, Eta-prime, and vector, Omega, Rho, Phi, mesons in NN collisions at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. It is shown that a good description of cross sections and angular distributions, for vector meson production, can be accomplished by considering meson and nucleon currents only, while for pseudo scalar production an inclusion of nucleon resonances is needed. The di-electron production from subsequent Dalitz decay of the produced mesons, $η'\to γγ^* \toγe^+e^-$ and $ω\to πγ^*\to πe^+e^-$ is also considere…
We review selected recent Belle results in quarkonium physics, that include precision measurement of the eta_b(1S) parameters, evidence for the eta_b(2S); evidence for the psi_2(1D); observation of the psi(4040) and psi(4160) transitions to J/psi eta with anomalously high rates; observation of the Upsilon(5S) transitions to Upsilon(1D)pi+pi- and Upsilon(1S,2S)eta. The low excitations of charmonium and bottomonium are in agreement with the Lattice QCD and effective theories calculations, while high excitations show unexpected properties.
We present the results of our recent analyses of the form factors F_pi(Q^2) and F_{P gamma}(Q^2), P = pi, eta, eta', within the local-duality version of QCD sum rules. To probe the expected accuracy of this method, we consider, in parallel to QCD, a quantum-mechanical potential model. In the latter case, the exact form factor may be calculated from the solutions of the Schrödinger equation and confronted with the result from the quantum-mechanical local-duality sum rule. We find that the local-duality sum rule is expected to yield reliable predictions for both F_pi(Q^2) and F_{pi gamma}(Q^2) i…
The ratio eta/s, shear viscosity (eta) to entropy density (s), reaches its local minimum at the (second order) phase transition temperature in a wide class of systems. It was suspected that this behavior might be universal. However, a counterexample is found in a system of two weakly self-interacting real scalar fields with one of them condensing at low temperatures while the other remains in the symmetric phase. There is no interaction between the two fields. The resulting eta/s is monotonically decreasing in temperature despite the phase transition.
The $η$ transition form factor is analysed for the first time in both space- and time-like regions at low and intermediate energies in a model-independent approach through the use of rational approximants. The $η\rightarrow e^+e^-γ$ experimental data provided by the A2 Collaboration in the very low energy region of the dilelectron invariant mass distribution allows for the extraction of the most precise up-to-date slope and curvature parameters of the form factors as well as their values at zero and infinity. The impact of these new results on the mixing parameters of the $η$-$η^\prime$ system…
The low $Q^2$ slopes of the the transition form factors provide a unique method to measure the sizes of the neutral pseudo-scalar mesons, since they do not have electromagnetic form factors. From the slope one obtains the "axial transition RMS radius" $ R_{PS,A} = \sqrt{<r^2>}$ for each PS meson. The present status of theory and experiment for these quantities are presented. A comparison of the $ R_{PS,A}$ is presented along with the electromagnetic and scalar radii of the $π^{\pm}$ mesons and the proton. We observe the striking similarity of the values of axial transition radii of all of the …
The rich phenomena of the shear viscosity (eta) to entropy density (s) ratio, eta/s, in weakly coupled N-component scalar field theories are studied. eta/s can have a "double dip" behavior due to resonances and the phase transition. If an explicit goldstone mass term is added, then eta/s can either decrease monotonically in temperature or, as seen in many other systems, reach a minimum at the phase transition. We also show how to go beyond the original variational approach to make the Boltzmann equation computation of eta systematic.
