Inspired by light-front holography, we compute the pion mass, charge radius, decay constant, electromagnetic form factor and electromagnetic transition form factor. To do so, we model the longitudinal quark dynamics using potentials due to 't Hooft and to Li & Vary. We find a longitudinal wavefunction that is rather more peaked about $x \sim 1/2$ than in previous studies. We also explore the strong degeneracy between these two potentials and conclude by noting that one scenario that accords well with the data also maps onto an equation previously noted by Vegh that describes the dynamics of a four-segmented string in $\mathrm{AdS}_3$.
We study the Wigner distributions of the pion using a holographic light-front pion wavefunction with dynamical spin effects to reveal its multidimensional structure.
We report that the inclusion of dynamical spin effects in the pion holographic light-front wavefunction leads to a remarkable improvement in describing pion observables (pion mean charge radius, decay constant, spacelike electromagnetic form factor) without the need to invoke higher Fock state contributions and/or a special AdS/QCD mass scale for the pion.
Using light-front holography, we predict simultaneously the pion decay constant and the pion charge radius by taking into account (higher twist) dynamical spin effects whose relative importance is constrained by QCD.
We show that the holographic Schrödinger equation of light-front chiral QCD, together with the 't Hooft equation of (1+1)-dimensional QCD in the large $N_c$ limit, can simultaneously describe pion spectroscopy as well as the pion decay constant, charge radius, electromagnetic form factor, photon-to-pion transition form factor, Parton Distribution Function (PDF) and Distribution Amplitude (DA). Furthermore, the chiral-limit constraints, as encoded in the Gell-Mann-Oakes-Renner (GMOR) relation, are satisfied.
Using the light-front holographic model, we study the transverse momentum dependent parton distributions (TMDs) for the case of pion. At leading twist, the unpolarized parton distribution function $ f_{1π}(x,\bfk^{2}) $ and the Boer-Mulders function $ h_{1π}^{\bot}(x,\bfk^{2}) $ are obtained for pion. We calculate both the functions using the light-front holographic model with spin improved wave function and compare the predicted results with available results of other models. In order to provide inputs in predicting future experimental data, a LO evolution is performed from model scale to exp…
We investigate the quark Wigner distributions of the pion to reveal the multidimensional picture of pion. We have used the spin improved wave functions of pion deduced from the light-front holographic model of mesons. By using the Fock-state overlap representation, the Wigner distributions of an unpolarized, longitudinally polarized and transversely polarized quark inside the pion are calculated. We have presented the results of transverse Wigner distributions in impact-parameter space as well as in momentum space. In order to understand the role of skewness which gives the longitudinal moment…
Pion parton distribution functions and pion-nucleus induced $J/ψ$ production in extended light-front holographic QCD
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；State Key Laboratory of Heavy Ion Science and Technology（重离子物理国家重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）
We predict the twist-2 Transverse Momentum Dependent parton distribution functions (TMDs) of the pion, namely the unpolarized quark TMD, $f_{1}(x, k_\perp)$, and the transversely polarized quark TMD, also known as the Boer-Mulders function, $h^\perp_{1}(x, k_\perp)$, using a holographic light-front pion wavefunction with dynamical spin effects. These spin effects, in conjunction with gluon rescattering, are crucial to predict a non-zero holographic Boer-Mulders function. We investigate the use of a non-perturbative SU(3) gluon rescattering kernel, thus going beyond the usual approximation of p…
利用量子色动力学的全息对偶模型，我们计算了类空动量转移区的π介子电磁形状因子F_pi（Q^2），以及π介子与矢量介子g_rho^（n）pi_pi的耦合。自发和明确的手征对称性破缺是这个特殊的全息模型的内在特征。我们考虑了具有“硬壁”和"软壁“红外截止值的变体，发现F_pi（Q^2）数据倾向于更接近硬壁模型的预测，尽管两者对于大Q^2来说都太浅。通过允许软壁模型的参数（最初由可观测量（如m_rho）固定）发生变化，人们发现拟合往往更符合F_pi（Q^2）。我们还计算了各种参数选择下的π介子电荷半径<r_pi^2>，并使用f^（n）_rho、g_{rho^(n) pi pi}和m^（n）_rho的值来观察ρ极点对F_pi（0）的饱和。
The valence-quark distribution function of the pion has been of interest for decades; particularly, the profile it should adopt when $x\to1$ (the large-$x$ behavior) is subject of a long-standing debate. In the light-front holographic QCD (LFHQCD) approach, this behavior is controlled by the so called reparametrization function, $w_τ(x)$, which is not fully determined from first principles. We show that, owing to the flexibility of $w_τ(x)$, the large-$x$ profile $u^π(x)\sim (1-x)^{2}$ can be contained within the LFHQCD formalism. This is in contrast with a previous LFHQCD study~(Guy F. de Ter…
Low-energy photon and pion scattering in holographic QCD
使用全息模型，其中手征对称性通过IR b.c.被打破。的，我们确定了一组新的QCD矩阵元素之间的关系。特别地，我们发现三个过程pi pi-> pi pi、gamma gamma-> pi pi和gamma-> pi pi pi的振幅涉及由EoM格林函数的适当的5D积分给出的单个标量函数h（Q^2）。在一个现象学分析的gamma gamma-> pi pi，我们发现一个整体协议与实验截面的能量范围很广。此外，在低能量下的极化率显示全息方法，以前的计算和实验之间的公平协议。
We consider phenomenological consequences arising from simple analytic solutions for holographic heavy-ion collisions. For these solutions, early-time longitudinal flow is initially negative (inward), sizable direct, elliptic, and quadrangular flow is generated, and the average vorticity of the system is tunable by a single parameter. Despite large vorticity and angular momentum, we show that the system does not complete a single rotation.
The breaking of chiral symmetry in holographic light-front QCD is encoded in its longitudinal dynamics with its chiral limit protected by the superconformal algebraic structure which governs its transverse dynamics. The scale in the longitudinal light-front Hamiltonian determines the confinement strength in this direction: It is also responsible for most of the light meson ground state mass consistent with the Gell-Mann-Oakes-Renner constraint. Longitudinal confinement and the breaking of chiral symmetry are found to be different manifestations of the same underlying dynamics as found in 't Ho…
We study one pion emission decay of the first excited state of the nucleon with negative parity $N(1535) \equiv N^*$ in the holographic model of QCD. The excited state is described as a vibrational mode along the extra $z$ direction in the five-dimensional space-time of the model. We have obtained an analytic formula for the axial coupling of $g_A^{NN^*}$. The off-diagonal axial coupling is obtained at the decaying pion momentum $|\boldsymbol{k}| = 448$ MeV as $g_A^{NN^*} \sim 0.32$, and hence a partial decay width $Γ_{N^* \to πN} \sim 30$ MeV, which is smaller than but reasonably compared to …
We show the 't Hooft Equation and the light-front holographic Schrödinger Equation are complementary to each other in governing the transverse and longitudinal dynamics of colour confinement in quark-antiquark mesons. Together, they predict remarkably well the light, heavy-light and heavy-heavy meson spectroscopic data. The universal emerging hadronic scale of light-front holography, $κ\approx 0.5$ GeV, controls the transverse dynamics of confinement in all mesons. In heavy-heavy mesons, it also coincides numerically with the 't Hooft coupling which governs longitudinal confinement, thus refle…
The total and differential cross sections of high energy pion-proton and pion-pion scattering are investigated in a holographic QCD model, focusing on the Regge regime in which the Pomeron exchange gives the dominant contribution to those cross sections. The Pomeron is described by the Reggeized spin-2 particle propagator, and the hadron-Pomeron couplings are given by gravitational form factors of the hadrons, which are obtained from the bottom-up AdS/QCD models. Since the parameters, which characterize the Pomeron trajectory, have been determined in a preceding study of the proton-proton scat…
The holographic light-front QCD framework provides a unified nonperturbative description of the hadron mass spectrum, form factors and quark distributions. In this article we extend holographic QCD in order to describe the gluonic distribution in both the proton and pion from the coupling of the metric fluctuations induced by the spin-two Pomeron with the energy momentum tensor in anti--de Sitter space, together with constraints imposed by the Veneziano model{\color{blue},} without additional free parameters. The gluonic and quark distributions are shown to have significantly different effecti…
We extend our previous calculations of the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment in holographic QCD to models with finite quark masses and a tower of massive pions. Analysing the role of the latter in the Wess-Zumino-Witten action, we show that the Melnikov-Vainshtein short-distance constraint is satisfied solely by the summation of contributions from the infinite tower of axial vector meson contributions. There is also an enhancement of the asymptotic behavior of pseudoscalar contributions when their infinite tower of excitations is summed, but …
