Transferring large files to remote sites is revisited in the light of two new de- velopments. The UK academic network has now been upgraded to SuperJANET5. The successor service to HPCx, the HECToR machine, will be located at the ACF, University of Edinburgh. Transferring data to HECToR from HPCx will be an important issue for the new service.

We present results for the static interquark potential, lightest glueballs, light hadron spectrum, and topological susceptibility using a nonperturbatively improved action on a 16(3) x 32 lattice at a set of values of the bare gauge coupling and bare dynamical quark mass chosen to keep the lattice size fixed in physical units (similar to1.7 fm). By comparing these measurements with a matched quenched ensemble, we study the effects due to two degenerate flavors of dynamical quarks, With the greater control over residual lattice spacing effects which these methods afford, we find some evidence of charge screening and some minor effects on the light hadron spectrum over the range of quark masses studied (M-PS/M-V greater than or equal to 0.58, where PS denotes pseudoscalar and V denotes vector). More substantial differences between quenched and unquenched simulations are observed in measurements of topological quantities.

We investigate instability and reversibility within hybrid Monte Carlo simulations using a nonperturbatively improved Wilson action. We demonstrate the onset of instability as tolerance parameters and molecular dynamics step sizes are varied. We compare these findings with theoretical expectations and present limits on simulation parameters within which a stable and reversible algorithm is obtained for physically relevant simulations. Results of optimization experiments with respect to tolerance parameters are also presented.

We present results for the hadron spectrum and static quark potential from a simulation with two flavours of O(a) improved dynamical Wilson fermions at β = 5.2. We address the issues of sea quark dependence of observables and finite-size effects.

UKQCD's dynamical fermion project uses the Generalised Hybrid Monte-Carlo (GHMC) algorithm to generate QCD gauge configurations for a non-perturbatively O(a) improved Wilson action with two degenerate sea-quark flavours. We describe our implementation of the algorithm on the Cray-T3E, concentrating on issues arising from code verification and performance optimisation, such as parameter tuning, reversibility, the effect of precision, the choice of matrix inverter and the behaviour of different molecular dynamics integration schemes.

UKQCD’s dynamical fermion project uses the Generalised Hybrid Monte Carlo (GHMC) algorithm to generate QCD gauge configurations for a non-perturbatively O(a) improved Wilson action with two degenerate sea-quark flavours. We describe our implementation of the algorithm on the Cray-T3E, concentrating on issues arising from code verification and performance optimisation, such as parameter tuning, reversibility, the effect of precision, the choice of matrix inverter, and the behaviour of different molecular dynamics integration schemes.

We compare the light hadron spectrum and decay constants for quenched QCD at $\beta=6.2$ using an $O(a)$-improved nearest-neighbour Wilson fermion action with those obtained using the standard Wilson fermion action on the same set of 18 gauge configurations. 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 increases slowly with quark mass as observed experimentally.

We present results for heavy-light decay constants, using both propagating quarks and the static approximation, in O(a)-improved, quenched lattice QCD. At β = 6.2 on a 243×48 lattice we find fD = 185 + 4 − 3 (stat) + 42 − 7 (syst) MeV, fB = 160 + 6 − 6 + 53 − 19 MeV, fDs/fD = 1.18 + 2 − 2 and fBs/fB = 1.22 + 4 − 3 , in good agreement with earlier studies. From the static theory we obtain f stat B = 253 + 16 − 15 + 105 − 14 MeV. We also present results from a simulation at β = 6.0 on a 163 × 48 lattice, which are consistent with those at β = 6.2. In order to study the effects of improvement, we present a direct comparison of the results using both the Wilson and the improved action at β = 6.0.

We measure accurate values of the inter-quark potentials on a 48356 lattice with SU(2) pure gauge theory at β = 2.85. The scale is set by extracting the strg tension - we obtain √Kα = 0.063 (3) at β = 2.85. From a careful study of the small-R potentials in the region 2 GeV < R−1 < 5 GeV, we extract a running coupling constant α(R).

We compute the hyperfine splitting m(J/psi)-m(etac) on the lattice, using both the Wilson and O(a)-improved (clover) actions for quenched quarks. The computations are performed on a 24(3)x48 lattice at beta=6.2, using the same set of 18 gluon configurations for both fermion actions. We find that the splitting is 1.83(-15)+13 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(etac) and f(J/psi)-1, both of which are considerably larger when computed using the clover action than with the Wilson action. For example for the ratio f(J/psi)-1/f(rho)-1 we find 0.32(-2)+1 with the Wilson action and 0.48+/-3 with the clover action (the physical value is 0.44(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 beta=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)x48 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.

Numerical results for the chiral-symmetry-breaking phase transition in non-compact QED with a four-fermion interaction, obtained using staggered fermions and an 84 lattice, are compared with the solution of the gap equation for the pure four-fermion model on the same size lattice. Agreement between the two suggests that there is no evidence for non-mean-field critical behaviour in the numerical data.

Results are presented of a systematic evaluation of the capabilities of a Meiko computing surface for high energy physics FORTRAN farming.

Results are presented for the chiral-symmetry-breaking phase transition in the four-dimensional U(1)-gauge-invariant Nambu-Jona-Lasinio model, obtained from numerical simulations using an 84 lattice, extending results for non-compact QED. The phase diagram is consistent with that predicted by the quenched planar approximation to the Schwinger-Dyson equation for the fermion self-energy. The fermion-mass dependence of the chiral condensate does not support a linear extrapolation to zero mass in the critical region.

The Edinburgh Concurrent Supercomputer Project is built around a Meiko Computing Surface, with presently some 400 floating-point transputers and 1.6 Gbytes of memory. The first part of this paper gives a brief overview of the project's origins and status. In the second part we review the results of applications in high energy physics, including lattice gauge theory and Monte Carlo event simulation.