The glueball-to-vacuum matrix elements of local gluonic operators in scalar, tensor, and pseudoscalar channels are investigated numerically on several anisotropic lattices with the spatial lattice spacing ranging from 0.1fm -0.2fm. These matrix elements are needed to predict the glueball branching ratios in J/ψ radiative decays which will help identify the glueball states in experiments. Two types of improved local gluonic operators are constructed for a self-consistent check and the finite volume effects are studied. We find that lattice spacing dependence of our results is very weak and the continuum limits are reliably extrapolated, as a result of improvement of the lattice gauge action and local operators. We also give updated glueball masses with various quantum numbers.

No abstract

Low-dimensional long-range topological charge structure in the QCD vacuum Physical

A valence QCD theory is developed to study the valence quark properties of hadrons. To keep only the valence degrees of freedom, the pair creation through the Z graphs is deleted in the connected insertions; whereas, the sea quarks are eliminated in the disconnected insertions. This is achieved with a new "valence QCD" lagrangian where the action in the time direction is modified so that the particle and antiparticle decouple. It is shown in this valence version of QCD that the ratios of isovector to isoscalar matrix elements (e.g. F A /D A and F S /D S ratios) in the nucleon reproduce the SU (6) quark model predictions in a lattice QCD calculation. We also consider how the hadron masses are affected on the lattice and discover new insights into the origin of dynamical mass generation. It is found that, within statistical errors, the nucleon and the ∆ become degenerate for the quark masses we have studied (ranging from one to four times the strange mass). The π and ρ become nearly degenerate in this range. It is shown that valence QCD has the C, P, T symmetries. The lattice version is reflection positive. It also has the vector and axial symmetries, the latter leads to a modified partially conserved axial Ward identity. As a result, the theory has a U (2N F ) symmetry in the particle-antiparticle space. Through lattice simulation, it appears that this is dynamically broken down to U q (N F ) × U q(N F ). Furthermore, the lattice simulation reveals spin degeneracy in the hadron masses and various matrix elements. This leads to an approximate U q (2N F ) × U q(2N F ) symmetry which is the basis for the valence quark model. In addition, we find that the masses of N, ∆, ρ, π, a 1 , and a 0 all drop precipitously compared to their counterparts in the quenched QCD calculation. This is interpreted as due to the disapperance of the 'constituent' quark mass which is dynamically generated through tadpole diagrams. The origin of the hyper-fine splitting in the baryon is largely attibuted to the Goldstone boson exchanges between the quarks. Both of these are the consequences of lacking chiral symmetry in valence QCD. We discuss its implication on the models of hadrons.

We present a quenched lattice QCD calculation of spin-1/2 five-quark states with uudds quark content for both positive and negative parities. We do not observe any bound pentaquark state in these channels for either I = 0 or I = 1. The states we found are consistent with KN scattering states which are checked to exhibit the expected volume dependence of the spectral weight. The results are based on overlap-fermion propagators on two lattices, 12 3 × 28 and 16 3 × 28, with the same lattice spacing of 0.2 fm, and pion mass as low as ∼ 180 MeV.

Results for the isovector axial form factors of the proton from a lattice QCD calculation are presented for both point-split and local currents. They are obtained on a quenched 16 3 × 24 lattice at β = 6.0 with Wilson fermions for a range of quark masses from strange to charm. For each quark mass, we find that the axial form factor falls off slower than the corresponding proton electric form factor. Results extrapolated to the chiral limit show that the q 2 dependence of the axial form factor agrees reasonably well with experiment. The axial coupling constant g A calculated for the local and the point-split currents is about 6% and 12% smaller than the experimental value respectively.

We present a calculation of the strangeness and charmness contents N |ss|N and N |cc|N of the nucleon from dynamical lattice QCD with 2 + 1 flavors. The calculation is performed with overlap valence quarks on 2+1-flavor domain-wall fermion gauge configurations. The configurations are generated by the RBC collaboration on a 24 3 × 64 lattice with sea quark mass am l = 0.005, am s = 0.04, and inverse lattice spacing a −1 = 1.73 GeV. Both actions have chiral symmetry which is essential in avoiding contamination due to the operator mixing with other flavors. Nucleon propagator and the quark loops are both computed with stochastic grid sources, while low-mode substitution and low-mode averaging methods are used respectively which substantially improve the signal to noise ratio. We obtain the strangeness matrix element f Ts = m s N |ss|N /M N = 0.0334(62), and the charmness content f Tc = m c N |cc|N /M N = 0.094(31) which is resolved from zero by 3 σ precision for the first time.

No abstract