W. Tross

Lbe Simulations Of Rayleigh-Bénard Convection On The Ape100 Parallel Processor

In this paper we describe an implementation of the Lattice Boltzmann Equation method for fluid-dynamics simulations on the APE100 parallel computer. We have performed a simulation of a two-dimensional Rayleigh-Benard convection cell. We have tested the theory proposed by Shraiman and Siggia for the scaling of the Nusselt number vs. Rayleigh number.

The hadronic mass spectrum in quenched lattice QCD: β=5.7

Abstract We compute the QCD hadronic mass spectrum in quenched lattice QCD at β=5.7 with small statistical and systematic errors by using the APE computer.

A HARDWARE IMPLEMENTATION OF THE APE100 ARCHITECTURE

APE100 processors are based on a simple Single Instruction Multiple Data architecture optimized for the simulation of Lattice Field Theories or other complex physical systems. This paper describes the hardware implementation of the first APE100 machine.

THE APE-100 COMPUTER: (I) THE ARCHITECTURE

We describe APE-100, a SIMD, modular parallel processor architecture for large scale scientific computation. The largest configuration that will be implemented in the present design will deliver a peak speed of 100 Gflops. This performance is, for instance, required for high precision computations in Quantum Chromo Dynamics, for which APE-100 is very well suited.

The Software Of The Ape100 Processor

We describe the software environment available for the APE100 parallel processor. We discuss the parallel programming language that we have defined for APE100 and its optimizing compiler. We then describe the operating system that allows to control APE100 from a host computer.

The hadronic mass spectrum in quenched lattice QCD: Results at β = 5.7 and β = 6.0

Abstract We study the hadronic mass spectrum in quenched lattice QCD. We present the results of numerical simulations done at β = 5.7 and β = 6.0. B and A1 meson masses get much closer to the physical values at β = 6.0, and so do the baryonic splittings. The mass ratio m p m p in the chiral limit tends to be from 10 to 20% higher than the experimental value. We estimate the nucleon σ term from the proton mass slope.

The deconfining phase transition in lattice gauge SU(3)

Abstract By using a source method and improved measuring techniques, we study the decay of the Polyakov loop in SU(3) lattice gauge theory at finite temperature. Our aim is to measure the correlation length of the system in the neighbourhood of the critical point. We work with lattices of size up to 162×64×4. We found that the maximum correlation length is only bounded by the spatial dimension of the lattice. This result is the one expected in a second order phase transition and appears to be incompatible with the presence of the strong first order transition claimed in the literature.

β=6.0 quenched Wilson fermions

Abstract We discuss the Ape Collaboration recent results for the Wilson fermions hadronic mass spectrum at β =6.0 on a 24 3 × 32 lattice. Some of the main new points are the results for the nucleon σ term and the estimates for excited states.

Staggered fermions at β = 5.7: Smeared operators on large lattices

Abstract We study staggered quenched QCD at a moderate value of β on large lattices. We introduce smeared Green functions for staggered fermions, and we analyze their effectiveness. We estimate the lattice spacing, and establish that staggered fermions undergo large systematic errors at low β in the estimate of the lattice spacing from the ϱ-mass. The scale ratio of the baryonic and the mesonic sector (mp/mp) is, on the contrary, consistent with the one estimated by using Wilson fermions. Owing to the use of smeared operators on large lattices (up to 243 × 32), we are able to give reliable results for the baryonic states.

A high statistics lattice calculation of ƒB in the static limit on APE

We present a high statistics calculation of ƒB in the static limit. The results have been obtained by numerical simulation of quenched QCD, at β = 6.0 on a 183 × 32 lattice. We compare ƒB calculated by using the Wilson and the Clover quark actions. The decay constant is obtained by studying heavy-light correlation functions of different smeared operators, on a sample of 210 gauge field configurations. We find that cubic smearings of size Ls ⩽ 3 or Ls ⩾ 9 are bad projectors on the lightest pseudoscalar state. Combining the information coming from smearing Ls = 5 and Ls = 7, we have obtained ƒB = 370±40 MeV in the clover case and ƒB = 350±40±30 MeV in the Wilson case. Our results support a large value of the pseudoscalar decay constant in the static approximation.