arXiv subjects
Publications and source records attributed to J. I. Skullerud.
We compute correlators and spectral functions for J/psi and eta_c mesons at nonzero momentum on anisotropic lattices with Nf=2. We find no evidence of significant momentum dependence at the current level of precision. In the pseudoscalar channel, the ground state appears to survive up to T~450MeV or 2.1T_c. In the vector channel, medium modifications may occur at lower temperatures.
We present our preliminary analysis for the chamonium and D$_s$ spectra obtained from N$_f=2$ dynamical anisotropic lattices. We use 12$^3\times 80$ lattices with lattice spacing $a_t=7.35$ GeV$^{-1}$ and anisotropy of six. Meson correlators are computed using all-to-all propagators together with variational analysis.
We present results for charmonium correlators and spectral functions in 2-flavour CD on anisotropic lattices. Our results indicate that the S-waves (J/psi and eta_c) survive up to temperatures close to 2T_c, while the P-waves (chi_c0 and chi_c1) melt away below 1.2T_c.
Charmonium systems in two-flavour QCD at non-zero temperature are studied at, and above the deconfining transition. Using anisotropic lattices the MEM approach is used to extract spectral functions for these channels. By carefully varying some of the irrelevant parameters in the MEM procedure, we confirm that our systematic effects are under control. The eta_c and J/psi states are found to persist at temperatures >~ 1.3 T_c in agreement with our previous dynamical studies.
We compute charmonium spectral functions in 2-flavour QCD using the maximum entropy method and anisotropic lattices. We find that the S-waves (J/psi and eta_c) survive up to temperatures close to 2T_c, while the P-waves (chi_c0 and chi_c1) melt away below 1.3T_c.
We report on a study of charmonium at high temperature in 2-flavour QCD. This is the first such study with dynamical fermions. Using an improved anisotropic lattice action, spectral functions are extracted from correlators in the vector and pseudoscalar channels. No signs of medium-induced suppression of the ground states are seen for temperatures up to 1.5T_c, while at T~2T_c there are clear signs of modifications. The current systematic and statistical uncertainties in our data, in particular the relatively coarse lattice and small volume, do not allow us to draw a firm conclusion at this stage.
The complete tensor structure of the quark--gluon vertex in Landau gauge is determined at two kinematical points (`asymmetric' and `symmetric') from lattice QCD in the quenched approximation. The simulations are carried out at beta=6.0, using a mean-field improved Sheikholeslami-Wohlert fermion action, with two quark masses ~ 60 and 115 MeV. We find substantial deviations from the abelian form at the asymmetric point. The mass dependence is found to be negligible. At the symmetric point, the form factor related to the chromomagnetic moment is determined and found to contribute significantly to the infrared interaction strength.
The DESY-Swansea Collaboration performed numerical simulations investigating SU(2) lattice gauge theory at non-zero chemical potential with one staggered quark flavour in the adjoint representation. This lattice model has similar features to QCD itself and its study gives interesting insights into some open problems of high density quark matter. In particular the role of the ``sign problem'' can be clarified in connection with diquark condensation and the phase diagram.
The quark propagator is calculated in the Landau gauge at beta=6.0. A method for removing the dominant, tree-level lattice artefacts is presented, enabling a calculation of the momentum-dependent dynamical quark mass.
The Landau gauge gluon propagator for the pure gauge theory is evaluated on a 32^3x64 lattice with a physical volume of (3.35^3x6.7)fm^4. Comparison with two smaller lattices at different lattice spacings allows an assessment of finite volume and finite lattice spacing errors. Cuts on the data are imposed to minimize these errors. Scaling of the gluon propagator is verified between beta=6.0 and beta=6.2. The tensor structure is evaluated and found to be in good agreement with the Landau gauge form, except at very small momentum values, where some small finite volume errors persist. A number of functional forms for the momentum dependence of the propagator are investigated. The form D(q^2)=D_ir+D_uv, where D_ir(q^2) ~ (q^2+M^2)^-ηand D_uv is an infrared regulated one-loop asymptotic form, is found to provide an adequate description of the data over the entire momentum region studied - thereby bridging the gap between the infrared confinement region and the ultraviolet asymptotic region. The best estimate for the exponent ηis 3.2(+0.1/-0.2)(+0.2/-0.3), where the first set of errors represents the uncertainty associated with varying the fitting range, while the second set of errors reflects the variation arising from different choices of infrared regulator in D_uv. Fixing the form of D_uv, we find that the mass parameter M is (1020+/-100)MeV.
The gluon propagator has been calculated for quenched QCD in the Landau gauge at beta=6.0 for volumes 16^3x48 and 32^3x64, and at beta=6.2 for volume 24^3x48$. The large volume and different lattice spacings allow us to identify and minimise finite volume and finite lattice spacing artefacts. We also study the tensor structure of the gluon propagator, confirming that it obeys the lattice Landau gauge condition.
Scaling of the Landau gauge gluon propagator calculated at beta=6.0 and at beta=6.2 is demonstrated. A variety of functional forms for the gluon propagator calculated on a large (32^3x64) lattice at beta=6.0 are investigated.
The gluon propagator in Landau gauge is calculated in quenched QCD on a large (32^3X64) lattice at beta=6.0. In order to assess finite volume and finite lattice spacing artefacts, we also calculate the propagator on a smaller volume for two different values of the lattice spacing. New structure seen in the infrared region survives conservative cuts to the lattice data, and serves to exclude a number of models that have appeared in the literature.
The gluon propagator in the Landau gauge is calculated in quenched QCD on a large lattice (32^3x64) at beta=6.0. In order to assess finite volume and finite lattice spacing artefacts, we also calculate the propagator on a smaller volume for two different values of the lattice spacing. New structure seen in the infrared region survives conservative cuts to the lattice data, and serves to exclude a number of models that have appeared in the literature.
The gluon propagator is calculated in quenched QCD for two different lattice sizes (16^3x48 and 32^3x64) at beta=6.0. The volume dependence of the propagator in Landau gauge is studied. The smaller lattice is instrumental in revealing finite volume and anisotropic lattice artefacts. Methods for minimising these artefacts are developed and applied to the larger lattice data. New structure seen in the infrared region survives these conservative cuts to the lattice data. This structure serves to rule out a number of models that have appeared in the literature. A fit to a simple analytical form capturing the momentum dependence of the nonperturbative gluon propagator is also reported.
We present results for the QCD running coupling obtained from measuring the quark-gluon vertex in Landau gauge with suitable renormalisation conditions. The issue of discretisation errors arising from the fermion action is discussed.
We discuss strategies for using lattice QCD to investigate some topics in strong interaction phenomenology which are usually related to soft pomeron exchange. These include hadronic cross-sections at high energies and diffractive scattering at HERA. Some numerical results are presented in the framework of the Landshoff-Nachtmann pomeron model.
We investigate the phenomenology of the Landshoff-Nachtmann two-gluon-exchange model of the Pomeron using gluon propagators computed in the Landau gauge within quenched lattice QCD simulations. As the propagators have been evaluated entirely from QCD first principles, our results provide a consistency check of the model. Finally, we report a proposal to investigate the structure of the Pomeron-quark vertex, using a colour-singlet Pomeron source constructed from the gauge fields.