P.S. Paolucci

Glueball masses and string tension in lattice QCD

We study glueball masses in lattice QCD. We present the first numerical determination of the mass of the lowest spin 2 state in the scaling region, and find that it is close to the lowest spin 0 state. We present very precise results for the string tension and for the spin 0 state, obtained by analyzing a large set of operators. We find that finite size effects are significant.

Lattice calculation of D- and B-meson semileptonic decays, using the clover action at β = 6.0 on APE

Abstract We present the results of a high statistics lattice calculation of hadronic form factors relevant for D - and B -meson semi-leptonic decays into light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge field configurations, generated in the quenched approximation, at β = 6.0, on a 18 3 × 64 lattice, using the O ( α )-improved SW-Clover action. From the study of the matrix element 〈 K − |J μ |D 0 〉, we obtain f + (0) = 0.78 ± 0.08 and from the matrix element 〈 K ∗0 |J μ |D + 〉 we obtain V (0) = 1.08 ± 0.22, A i (0) = 0.67 ± 0.11 and A 2 (0) = 0.49 ± 0.34. We also obtain the ratios V(0) A 1 (0) = 1.6 ± 0.3 and A 2 (0) A 1 (0) = 0.7 ± 0.4 . Our predictions for the different form factors are in good agreement with the experimental data, although, in the case of A 2 (0), the errors are still too large to draw any firm conclusion. With the help of the Heavy Quark Effective Theory (HQET) we have also extrapolated the lattice results to B -meson decays. The form factors follow a behaviour compatible with the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at β = 6.4, using the standard Wilson action.

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.

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.

GLUEBALL MASSES AND THE LOOP LOOP CORRELATION-FUNCTIONS

Abstract We analyse the pure gauge lattice QCD by measuring loop-loop correlation functions on a 12 3 ×32 lattice at β =5.9. We select a set of operators given by the smearing procedure. We obtain a good estimate of the mass of the 0 ++ state and for the string tension, and upper bounds for the masses of the 2 ++ and the 1 +− states.

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.

APEnet+: a 3D Torus network optimized for GPU-based HPC Systems

In the supercomputing arena, the strong rise of GPU-accelerated clusters is a matter of fact. Within INFN, we proposed an initiative — the QUonG project — whose aim is to deploy a high performance computing system dedicated to scientific computations leveraging on commodity multi-core processors coupled with latest generation GPUs. The inter-node interconnection system is based on a point-to-point, high performance, low latency 3D torus network which is built in the framework of the APEnet+ project. It takes the form of an FPGA-based PCIe network card exposing six full bidirectional links running at 34 Gbps each that implements the RDMA protocol. In order to enable significant access latency reduction for inter-node data transfer, a direct network-to-GPU interface was built. The specialized hardware blocks, integrated in the APEnet+ board, provide support for GPU-initiated communications using the so called PCIe peer-to-peer (P2P) transactions. This development is made in close collaboration with the GPU vendor NVIDIA. The final shape of a complete QUonG deployment is an assembly of standard 42U racks, each one capable of 80 TFLOPS/rack of peak performance, at a cost of 5 k€/T F LOPS and for an estimated power consumption of 25 kW/rack. In this paper we report on the status of final rack deployment and on the R&D activities for 2012 that will focus on performance enhancement of the APEnet+ hardware through the adoption of new generation 28 nm FPGAs allowing the implementation of PCIe Gen3 host interface and the addition of new fault tolerance-oriented capabilities.

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.

Scaling in lattice QCD: Glueball masses and string tension

Abstract We study the scaling behaviour of lattice quantum chromodynamics by comparing the β dependence of the string tension and the 0 ++ glueball mass. We use a source method at β =5.7, β =5.9 and β =6.1, on lattices from 9 3 · 24 to 16 3 · 32. Assuming a string tension of about (420 MeV) 2 , the lattice spacing ranges from 0.16 to 0.08 fm. In order to separate finite volume from scaling violation effects we have compared data from lattices having approximately the same overall physical size at the different values of β. We find deviations from scaling to be very small.