Activities and Collaboration 1.

Division of Particle Physics and Astrophysics
Computational Particle Physics Group
Sinya AOKI
Graduate School of Pure and Applied Sciences,
University of Tsukuba

Elementary Particle Physics• What is the most fundamental constituent in Nature ?
Nucleon (proton,neutron)

Atomelectron
Nucleus

gluon
quark

• What is the fundamental law in Nature ?
• electromagnetic interaction Weinberg-Salam model(Electroweak interaction)• weak interaction (β decay)• strong interaction (nuclear force) Quantum ChromoDynamics(QCD)
Grand Unified Theory (GUT) ?

• Gravity
String theory ?
standard model of elementary particle = Weinberg-Salam model + QCD

Quantum ChromoDymanics (QCD)• Dynamics of quarks and gluons• “hadrons” are bound states of quarks• interaction is “strong”• perturbative expansion in coupling is not

Nucleongluon

reliable.

Electroweak interaction• processes involving hadrons are affected by thisinteraction.

• effects of QCD must be included for reliablepredictions from the standard model.

• it is also necessary to investigate possibilities“beyond the standard model”.

quark

Lattice QCD• define QCD on discrete space-time (lattice)• suitable for strong interaction• Numerical simulations are possible for lattice QCD• generate “gluon fields” by Monte-Carlo method• behavior of “quarks” is calculated on “gluon fields”• huge computational powers are required.

Activities of computational particle physics group• Researches in lattice QCD using super-computer• fundamental properties of hadrons such as masses and decay constants
talk by Kuramashi• test of QCD/lattice QCD• more complicated quantities
talk by Yoshie• U(1) problem
talk by Ishizuka• ρ meson decay
talk by Ishii• nuclear force• QCD effects to electroweak process for Kobayashi-Maskawa matrix
talk by Taniguchi• hardonic matrix elements of CP violation• ILDG/JLDG• store “gluon fields” for public uses

Group members

A. Ukawa (Prof.)

T.Yoshie (Assoc. Prof.)

K. Kanaya (Prof.)

S. Aoki (Prof.)

Graduate School ofPure and Applied Sciences

N. Ishizuka (Assoc. Prof.)

Y. Kuramashi (Lecturer)+ 6 postdoctoral fellows+ 6 graduate students

CCS
Y. Taniguchi (Asst. Prof.)Collaborations in CCS• Construction of PACS-CS• Division of High Performance Computing Systems (Sato, Boku,Tatebe, Takahashi)• Total system: regular meeting• Network: regular meeting• Operation• Tuning• Improvement of algorithms• Division of High Performance Computing Systems (Sakurai)• Inversion/Eigenvalue problem: regular meeting• ILDG/JLDG• Division of High Performance Computing Systems (Sato, Boku)

Research results: an example
Force between Nucleons(The nuclear force)
1935 H. Yukawa
The nuclear force

1949 Nobel prize

mesonsexchange of virtual particles
between nucleons

Modern nucleon-nucleon potentialr

Long range partIIIIIII

one pion exchange potential(OPEP)
Medium range partIIσ, ρ, ω exchange!"""#""$%&%

!!!

!!

!

III!!""#""'()"*)"+)",
2π exchange!!!"#""-./01"2(Taketani)

Short range part
repulsive core (RC)quark ?

Importance of repulsive core
9#:%;<" !"#$%&'
stability of nuclei
neutron star!"#$%&"'(QCD)()*+,(-

supernova
II-./$01
explosion./%01%!2345+,678

23456A ./$78:23;<!"

QCD;<!"

Origin of RC: “The most fundamental problem in Nuclear physics.”

Our results from lattice QCD
Ishii-Aoki-Hatsuda, 2007OPEPNot only a repulsion at short distance (RC)but also attractions at long-medium distances
are reproduced !