arXiv subjects

D. G. Richards

Publications and source records attributed to D. G. Richards.

44 records · Page 3Linked to original sources

arXiv1997

Alpha_s from the non-perturbatively renormalised lattice three-gluon vertex

We compute the running QCD coupling on the lattice by evaluating two-point and three-point off-shell gluon Green's functions in a fixed gauge and imposing non-perturbative renormalisation conditions on them. Our exploratory study is performed in the quenched approximation at beta=6.0 on 16^4 and 24^4 lattices. We show that, for momenta in the range 1.8-2.3 Gev, our coupling runs according to the two-loop asymptotic formula, allowing a precise determination of the corresponding Lambda parameter. The role of lattice artifacts and finite-volume effects is carefully analysed and these appear to be under control in the momentum range of interest. Our renormalisation procedure corresponds to a momentum subtraction scheme in continuum field theory, and therefore lattice perturbation theory is not needed in order to match our results to the MSbar scheme, thus eliminating a major source of uncertainty in the determination of alpha_MSbar. Our method can be applied directly to the unquenched case.

hep-lat↗

arXiv1997

The effect of tree-level and mean-field improvement on the light-hadron spectrum in quenched QCD

We compute the light hadron mass spectrum at beta=5.7 using the O(a) improved Sheikholeslami-Wohlert (SW) fermion action with two choices of the clover coefficient: the classical value, c=1, and a mean-field or tadpole-improved estimate c=1.57. We compare our results with those of the GF11 Collaboration who use the Wilson fermion action (c=0). We find that changing c from zero to 1 and 1.57 leads to significant differences in the masses of the chirally extrapolated and strange pseudoscalar and vector mesons, the nucleon, the Delta, and also in the Edinburgh plot. A number of other quantities, for example m_V^2-m_PS^2, J, am_K/am_ρand am_{K^*}/am_ρdo not appear to change significantly. We also investigate the effect of changing the lattice volume from approximately (2 fm)^3 to (2.6 fm)^3. We find that the meson masses are consistent to within one standard deviation and baryon masses are consistent to within two standard deviations.

hep-lat↗

arXiv1996

Soft Pomeron Physics on the Lattice

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.

hep-ph↗

arXiv1996

Lattice Study of the Pomeron

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.

hep-ph↗

arXiv1995

The Landshoff-Nachtmann Pomeron on the Lattice

We investigate the Landshoff-Nachtmann two-gluon-exchange model of the Pomeron using gluon propagators computed in the Landau gauge within quenched lattice QCD calculations. We first determine an effective gluon-quark coupling by constraining the Pomeron-quark coupling to its phenomenological value $β_0 = 2\, \gev^{-1}$. We then provide predictions for a variety of diffractive processes. As the propagators have been evaluated entirely from QCD first principles (although in the quenched approximation), our results provide a consistency check of the Landshoff-Nachtmann model. We address the issue of the possible gauge-dependence of our results, which will be the object of a future study.

hep-lat↗

arXiv1993

Strange Quark Physics on the Lattice

We present results for hadrons containing a strange quark in quenched lattice QCD. We calculate masses and decay constants using 60 gauge configurations with an O(a)-improved fermion action at beta = 6.2. Using the rho mass to set the scale, we find hadron masses within two to three standard deviations of experiment. Direct comparison with experiment for decay constants is obscured by uncertainty in current renormalisations. Finally, we present preliminary results on the semi-leptonic decay D->K. We find f_K^+(0)/Z_V = 0.75+5-4 and f_K^0(0)/Z_V = 0.74+4-4.

hep-lat↗

arXiv1992

The Hyperfine Splitting in Charmonium: Lattice Computations Using the Wilson and Clover Fermion Actions

We compute the hyperfine splitting $m_{J/ψ}-m_{η_c}$ on the lattice, using both the Wilson and $O(a)$-improved (clover) actions for quenched quarks. The computations are performed on a $24^3\times48$ lattice at $β= 6.2$, using the same set of 18 gluon configurations for both fermion actions. We find that the splitting is 1.83\err{13}{15} times larger with the clover action than with the Wilson action, demonstrating the sensitivity of the spin-splitting to the magnetic moment term which is present in the clover action. However, even with the clover action the result is less than half of the physical mass-splitting. We also compute the decay constants $f_{η_c}$ and $f^{-1}_{J/ψ}$, both of which are considerably larger when computed using the clover action than with the Wilson action. For example for the ratio $f^{-1}_{J/ψ}/f^{-1}_ρ$ we find 0.32\err{1}{2} with the Wilson action and $0.48\pm 3$ with the clover action (the physical value is 0.44(2)).

hep-lat↗

arXiv1992

Quenched Hadrons using Wilson and O(a)-Improved Fermion Actions at beta=6.2

We present the first study of the light hadron spectrum and decay constants for quenched QCD using an O(a)-improved nearest-neighbour Wilson fermion action at β=6.2. We compare the results with those obtained using the standard Wilson fermion action, on the same set of 18 gauge field configurations of a 24^3 times 48 lattice. For pseudoscalar meson masses in the range 330-800 MeV, we find no significant difference between the results for the two actions. The scales obtained from the string tension and mesonic sector are consistent, but differ from that derived from baryon masses. The ratio of the pseudoscalar decay constant to the vector meson mass is roughly independent of quark mass as observed experimentally, and in approximate agreement with the measured value.

hep-lat↗