Inferring theoretical predictions from the Standard Model (SM) of elementary particles, which explains most of the existing experimental and observational results of particle physics, often require numerical computation procedures to solve Quantum Chromo Dynamics (QCD) comprised in the SM. These include the predictions of the behavior of particle systems in extreme conditions such as high temperature and/or density, and precision tests of the SM using hadronic reactions as well as investigation of physics beyond the SM.
Numerical simulations with lattice QCD techniques using a realistic set of parameters are becoming feasible. However, many significant questions remain unsolved, which we are addressing by employing lattice methods while preserving as many important symmetries as possible—the symmetries often sacrificed to make the simulations less demanding. In order to use the post-K computer for such demanding computations, we will develop algorithms, analysis methods, and codes, while performing computation on existing HPC resources. In the first principle computations of the models, we aim to bridge the energy scale layers, and thereby reveal the nature of the evolution of the universe and the mechanism of matter creation in it.
Novel behavior of two-flavor QCD near phase transition
Phase structure of the two-flavor QCD, a model of real world QCD, which has actually three active dynamical quark flavors, is largely unexplained, including the order of phase transition. We are investigating the properties of phase transition employing a chirally invariant formulation of QCD on the lattice. The figure (from JLQCD collaboration) indicates a phase transition at around m=10 MeV and a temperature of T=220 MeV, which is surprisingly higher than the m=0 transition temperature of T=175 MeV. Follow-up study using the Oakforest-PACS is underway by varying the system size to infer results at the thermodynamic limit of the model. Codes for these studies as well as for the post-K computer is being developed in parallel with the computation, the aim being not only to investigate two-flavor thermodynamics, but also to perform general QCD simulations with three and more flavors.
Topological susceptibility as a function of quark mass in two-flavor QCD