We improve and extend our study of the complex in-medium heavy quark potential and its Debye mass $m_D$ in a gluonic medium with a finer scan around the deconfinement transition and newly generated ensembles closer to the thermodynamic limit. On the lattices with larger physical volume, Re[V] shows signs of screening, i.e. a finite $m_D$, only in the deconfined phase, reminiscent of a genuine phase transition. Consistently Im[V] exhibits nonzero values also only above $T_C$. We compare the behavior of Re[V] with the color singlet free-energies that have been used historically to extract the Debye mass. An effective coupling constant is computed to assess the residual influence of the confining part of the potential at $T>0$. Our previous finding of a gradual screening of Re[V] around $T_C$ on finer lattices is critically reassessed and interpreted to originate from finite volume artifacts that affect the deployed $β=7$, $ξ_b=3.5$ parameter set at $N_s=32$.
We present an exploratory study of the gluonic structure of the $ϕ$ meson using lattice QCD (LQCD). This includes the first investigation of gluonic transversity via the leading moment of the twist-two double-helicity-flip gluonic structure function $Δ(x,Q^2)$. This structure function only exists for targets of spin $J\ge1$ and does not mix with quark distributions at leading twist, thereby providing a particularly clean probe of gluonic degrees of freedom. We also explore the gluonic analogue of the Soffer bound which relates the helicity flip and non-flip gluonic distributions, finding it to…
We present the first study of the Abelian-projected gluonic-excitation energies for the static quark-antiquark (Q$\bar{\rm Q}$) system in SU(3) lattice QCD at the quenched level, using a $32^4$ lattice at $β= 6.0$. We investigate ground-state and three excited-state Q$\bar{\rm Q}$ potentials, using smeared link variables on the lattice. We find universal Abelian dominance for the quark confinement force of the excited-state Q$\bar{\rm Q}$ potentials as well as the ground-state potential. Remarkably, in spite of the excitation phenomenon in QCD, we find Abelian dominance for the first gluonic-e…
Gluonic excitation of non-exotic hybrid charmonium from lattice QCD
利用猝灭格点量子色动力学研究了具有非奇异量子数$J^{PC}=0^{-+}$、$1^{--}$和$1^{++}$的杂化粲偶素${\bar c} c g$的基态和第一激发态.它们在文献中被完全忽略，只是因为它们的基态与$η_c$，$J/ψ$和$χ_{c1}$简并，并且在实验中很难与这些常规的粲素介子区分开来。然而，我们在第一激发态中观察到了强的胶子径向激发，我们预测它们的质量分别为4.352（225）GeV、4.379（149）GeV和7.315（257）GeV，与相应的常规粲偶素的第一激发态完全不同。它们与最近发现的Y（4260）态的相关性和未来对其他态的实验研究也进行了讨论。
In this paper, one uses a damped potential to present a description of the running coupling constant of QCD in the confinement phase. Based on a phenomenological perspective for the Debye screening length, one compares the running coupling obtained here with both the Brodsky-de Téramond-Deur and the Richardson approaches. The results seem to indicate the model introduced here corroborate the Richardson approach. Moreover, the Debye screening mass in the confinement phase depends on a small parameter, which tends to vanish in the non-confinement phase of QCD.
The role of gluons in the structure of the nucleon and light nuclei is investigated using lattice quantum chromodynamics (QCD) calculations. The first moment of the unpolarised gluon distribution is studied in nuclei up to atomic number $A=3$ at quark masses corresponding to pion masses of $m_π\sim 450$ and $806$ MeV. Nuclear modification of this quantity defines a gluonic analogue of the EMC effect and is constrained to be less than $\sim 10$% in these nuclei. This is consistent with expectations from phenomenological quark distributions and the momentum sum rule. In the deuteron, the combina…
We perform real-time lattice simulations of nonequilibrium quark production in the longitudinally expanding QCD plasma. Starting from a highly occupied gluonic state with vacuum quark sector, we extract the time evolution of quark and gluon number densities per unit transverse area and rapidity. The total quark number shows after an initial rapid increase an almost linear growth with time. Remarkably, this growth rate appears to be consistent with a simple kinetic theory estimate involving only two-to-two scattering processes in small-angle approximation. This extends previous findings about t…
The concept of a screening mass is a powerful tool to simplify the intricate physics of in-medium test charges surrounded by light charge carriers. While it has been successfully used to describe electromagnetic properties, its definition and computation in QCD is plagued by questions of gauge invariance and the presence of non-perturbative contributions from the magnetic sector. Here we present a recent alternative definition of a gauge invariant Debye mass parameter following closely the original idea of Debye and Hueckel. Our test charges are a static heavy quark-antiquark pair whose comple…
The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $ξ$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributio…
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…
The spin-independent and transversity generalised form factors (GFFs) of the $ϕ$ meson are studied using lattice QCD calculations with light quark masses corresponding to a pion mass $m_π\sim450(5)$ MeV. One transversity and three spin-independent GFFs related to the lowest moments of leading-twist spin-independent and transversity gluon distributions are obtained at six non-zero values of the momentum transfer up to 1.2 GeV$^2$. These quantities are compared with the analogous spin-independent quark GFFs and the electromagnetic form factors determined on the same lattice ensemble. The results…
We study the topological structure of QCD by cluster analysis. The fermionic topological charge density is constructed from low lying modes of overlap Dirac operator for three types of temporal boundary conditions for fermion field. This gives the possibility to mark all three dyon constitutents of KvBLL caloron in gluonic fields. The gluonic topological charge density is appearing in the process of overimproved gradient flow process stopped at the moment when it maximally matches the fermionic topological charge density. This corresponds to the smearing of gluonic fields up to the scale set b…
The QCD topological observables are essential inputs to obtain theoretical predictions about axion phenomenology, which are of utmost importance for current and future experimental searches for this particle. Among them, we focus on the topological susceptibility, related to the axion mass. We present lattice results for the topological susceptibility in QCD at high temperatures obtained by discretizing this observable via spectral projectors on eigenmodes of the staggered Dirac operator, and we compare them with those obtained with the standard gluonic definition. The adoption of the spectral…
We briefly review and expand our recent analysis for all three invariant A,B,D gravitational form factors of the nucleon in holographic QCD. They compare well to the gluonic gravitational form factors recently measured using lattice QCD simulations. The holographic A-term is fixed by the tensor $T=2^{++}$ (graviton) Regge trajectory, and the D-term by the difference between the tensor $T=2^{++}$ (graviton) and scalar $S=0^{++}$ (dilaton) Regge trajectories. The B-term is null in the absence of a tensor coupling to a Dirac fermion in bulk. A first measurement of the tensor form factor A-term is…
We present preliminary lattice results for the topological susceptibility in high-$T$ $N_f=2+1$ QCD obtained discretizing this observable via spectral projectors on eigenmodes of the staggered operator, and we compare them with those obtained with the standard gluonic definition. The adoption of the spectral discretization is motivated by the large lattice artifacts affecting the continuum scaling of the gluonic susceptibility at high $T$, related to the choice of non-chiral fermions in the action.
We present results for the neutron electric dipole moment due to the dimension 4 and dimension 6 gluonic CP violation, and the isovector quark chromoelectric dipole moment using clover valence quarks on HISQ dynamical ensembles generated by the MILC Collaboration. For the gluonic operators, we use the gradient flow scheme to obtain divergence-free continuum results. For the chromoelectric dipole moment operator, we use the unflowed local operator but discuss how the quadratically divergent mixing with the pseudoscalar operator can be controlled nonperturbatively.
We combine techniques previously utilised to study flux tube field density profiles and to study the excited spectrum of the gluonic fields produced by a static quark-antiquark pair. Working with pure gauge SU(3) fields discretised in a lattice, we utilise Wilson loops with a large basis of gluonic spacelike Wilson lines to include different excitations of the quark-antiquark flux tube. To increase the signal over noise ratio, we use the multihit technique in the temporal Wilson lines and the APE smearing in spatial Wilson lines. The number of gluonic operators combined with the space points w…
