Lattice Quantum Chromodynamics (SPI, Mapping, Site Ordering, and QPX in Lattice QCD Code on Mira). ALCF-2 Early Science Program Technical Report.

摘要

Lattice QCD is a numerical method to simulate QCD (Quantum Chromodynamics) in- cluding non-perturbative effects. Among other methods, lattice QCD is the only successful non-perturbative method that can be systematically improved from first principles. Lattice QCD plays an important role in High Energy Particle Physics (flavor physics, spectroscopy, and beyond the Standard Model physics) and Nuclear Physics (nucleon/nuclear spectrum & structure, quark-gluon plasma, and the QCD equation of state). Moreover, recently there are active developments in applying lattice gauge theory to quantum field theory in general, for example the theoretical description of graphene or cold atom systems. We define the QCD action on a finite and discrete lattice like grid, so that we can compute the path integral (partition function) on a computer. A current lattice size is 96(3) x 192, and the corresponding number of degrees of freedom for the path integral is about 6 x 10(8). Thus, it requires enormous computing resources. In this report, we describe our overall efforts to improve lattice QCD software on Mira, which include a new communication library using the Message Unit (MU) SPI (System Programming Interface), better node mapping strategy, lattice site reordering, and using the quad floating point (QPX) intrinsics.