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Koji Harada Last modified date:2023.06.12

Professor / Graduate School of Science, Department of Physics
Division for Theoretical Natural Science
Faculty of Arts and Science

Graduate School
Other Organization
Administration Post
Vice President
Dean of the Faculty of Arts and Science
Director of the Admission Center

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 Reseacher Profiling Tool Kyushu University Pure
Academic Degree
Doctor of Science
Country of degree conferring institution (Overseas)
Field of Specialization
Theoretical Elementary Particle Physics
Total Priod of education and research career in the foreign country
Outline Activities
Research activity:
In the Standard Model of Elementary Particle Physics, hadrons, which participate in Strong Interactions, are described by the gauge field theory called Quantum Chromodynamics (QCD) and regarded as bound states of quarks and gluons. Due to the Confinement mechanism, quarks and gluons are never observed by themselves and only the composite particles, hadrons, are observed. It is therefore of primary importance to understand QCD bound states to really understand Strong Interactions. However, bound states in a relativistic field theory like QCD are complicated combinations of multi-particle states in which all of the quantum fluctuation scales are coupled: they are really very complicated non-perturbative dynamical systems.

QCD is the "ultimate theory" of Strong Interactions and is expected to be responsible (ultimately) for the (most of) structures and interactions of all hadrons, including various nuclei. It is however extremely difficult to explain the properties of (stable) nuclei directly in terms of QCD. After all, we usually exploit some phenomenological "realistic nuclear forces" to explain the properties, admittedly it is a very retrogressive way from the point of view that we already have the "ultimate theory". Although it is unlikely that we can describe nuclei directly in terms of quark-gluon degrees of freedom, it is worthwhile clarifying what we can say directly from the dynamics of QCD, without recourse to phenomenological models.

Following the idea given above, I study how to describe hadrons by using Effective Field Theory. Effective Field Theory is a framework which has the connection to QCD through chiral symmetry breaking, and allows systematic improvement of the approximation. In particular, I am interested in applying the ideas of Wilsonian Renormalization Group to Nuclear Effective Field Theory to figure out the characteristic features of the dynamics.
I studied high-density nuclear systems at low temperatures, which cannot be investigated in the lattice QCD approach, by using lattice simulations of the Nuclear Effective Field Theory.

Educational activity:
As a member of Faculty of Arts and Science, I am involved very much in education for the freshmen.
I also give seminars and have meetings for the graduates in the group of Theory of Subatomic Physics and Astrophysics beside giving everyday supervision.
Research Interests
  • Dynamical properties of the cosmological first-order phase transition
    keyword : false vacuum, phase transition, origin of the baryon asymmetry of the Universe, dark matter
  • Lattice simulations of finite-density nucleon systems based on nulear effective field theory
    keyword : lattice theory, effective field theory, numerical simulations
  • Application of nonperturbative renormalization group methods to three-body systems
    keyword : renormalization group, limit cycle, Efimov effect
  • Application of effective field theory to nuclear reactions
    keyword : effective field theory, nuclear reactions
    2008.09~2009.03We consider the applications of effective field theory to nuclear reactions at intermediate energies..
  • Apparently noninvariant terms in field theory with nonlinearly realized symmetries
    keyword : nonlinear sigma models, radiative corrections, perturbation theory
    2008.05~2009.08There emerge apparently noninvariant terms in nonlinearly realized field theories, such as nonlinear sigma models, in the effective potential calculated perturbatively. The emergence of such terms do not imply that the symmetry is lost. We show that such a phenomenon is a general feature and why they emerge..
  • Renormalization group analysis for the $V_{low k}$ potential
    keyword : renormalization group, effective interactions, nuclear forces
    2007.08~2008.04We pointed out that there are problems in the derivations of the renormalization group equation given in the literature for the so-called V_{low k} effective potential for the nuclear forces..
  • Wilsonian Renormalization Group and Nuclear Effective Field Thoery
    keyword : renormalization, effective field theory, nontrivial fixed point, power counting
    2004.04We analyze the behavior of Nuclear Effective Filed Theory(NEFT),which describe the interactions of nucleons at low energies, by using Wilsonian Renormalization Group. In particular, we determine the power counting of NEFT by the scaling dimensions of the operators..
  • An Effecitive Theory Approach to Skyrme Model and Application to Pentaquarks
    keyword : Skyrme model, pentaquark
    2003.02~2004.10We develop a new approach to Skyrme model based on the most general chiral effective theory of mesons. The theory contains a set of new interactions, which have never been considered. Based on this new theory, we compute some properties, such as masses and decay widths, of the recently discovered pentaquarks..
  • Large-$N_c$ QCD and nontriviality of low-energy effective field theory
    keyword : large-N_c, QCD, effective field theory, renormalization, renormalization group
    2001.07The purpose of the research is to show that it is possible to understand the "unnatural" bahaviors in the low-energy region of strong interactions in the light of $1/N_c$ expansion..
Academic Activities
1. Koji Harada, Pions are neither perturbative nor nonperturbative: Wilsonian renormalization-group analysis of nuclear effective field theory including pions, Physical Review D, 10.1103/PhysRevC.83.034002, 83, 3, 034002 [14 pages] , 2011.03.
2. Koji Harada, Hirofumi Kubo, Anomalous dimensions determine the power counting
Wilsonian RG analysis of nuclear EFT, Nuclear Physics B, 10.1016/j.nuclphysb.2006.10.001, 758, 3, 304-329, 2006.12, The Legendre flow equation, a version of exact Wilsonian renormalization group (WRG) equation, is employed to consider the power counting issues in nuclear effective field theory. A WRG approach is an ideal framework because it is nonperturbative and does not require any prescribed power counting rule. The power counting is determined systematically from the scaling dimensions of the operators at the nontrivial fixed point. The phase structure is emphasized and the inverse of the scattering length, which is identified as a relevant coupling, is shown to play a role of the order parameter. The relations to the work done by Birse, McGovern, and Richardson and to the Kaplan-Savage-Wise scheme are explained..
3. Koji Harada, Izumi Tsutsui, On the path-integral quantization of anomalous gauge theories, Physics Letters B, 10.1016/0370-2693(87)90970-1, 183, 3-4, 311-314, 1987.01, The path-integral quantization of anomalous gauge theories is discussed. From the necessity of the "gauge volume" integration, the Wess-Zumino action appears naturally and, as a consequence, the effective action becomes gauge invariant. An application to the chiral Schwinger model gives a concrete example..
Membership in Academic Society
  • The Physics Education Society of Japan
  • American Association of Physics Teachers
  • The Physical Society of Japan
  • Quantization of anomalous gauge theory
Educational Activities
At the Graduate School:
・Seminars on Elementary Particle Physics I (2001, 2005, 2010, 2013)
・Gauge Theory (2003, 2004, 2005, 2006, 2nd semester)
・Topics in Elementary Particle Physics (2007, 2008, 2009, 2010, 2011 2nd semester)
・Quantum Field Theory (2012,2013 1st semester)
・Elementary Particle Theory (2015 2nd semester(1/3), 2017 2nd semester)
・various kinds of study meetings in the lab.

At the Undergraduate School:
・Exercises in Electromagnetism (2000, 1st semester)
・Exercises in Physics (1/2) (2000, 1st semester)
・Frontier in Physics (particle physics part) (2000, 2001, 2002, 1st semester)
・Mechanics II (2002, 2003, 2004, 2005, 2006, 1st semester)
・Current Topics in Physics (particle physics part) (2002, 2003, 2004, 2011, 1st semester)
・Core Seminar (2006, 1st semester)
・Seminars in Physics I, II (2002, 2003, 2006, 2007, 2008, 2011, 2012)
・General Relativity (2003, 2004, 2005, 2006, 2007, 2nd semester; 2009, 2010, 2011 1st semester)
・Analytical Dynamics and Exercises (2007, 2008, 2009, 2010, 2011, 2012, 2013 1st semester)
・Quantum Mechanics II (2012,2013 1st semester)

At the Common Education:
・Fundamental Experiments in Physics (2000, 1st semester)
・Elementary Classical Mechanics and Exercises I (2002, 1st semester)
・Elementary Classical Mechanics and Exercises II (2000, 1st semester, 2001, 2002, 2nd semester)
・Elementary Classical Mechanics (2001, 1st semester)
・Elementary Electromagnetism (2001, 2002, 1st semester, 2001, 2nd semester)
・Heat and Waves (2001, 1st semester)
・Our Material World (1/4) (2002, 2004(twice), 2006, 1st semester)

At the KIKAN Education:
・KIKAN-Education Seminar ((2 classes)2014, (1 class)2015, (1 class)2016 1st semester),((1 class)2017,(1 class)2018,(1 class)2019, (1 class)2020, (1 class)2021, (2 classes)2022, summer quarter)
・Physics in Everyday Life (2014, 2015, 2016, 1st semester)
・Physics in Everyday Life A (2017,2018,2019,2020,2021, 2022, spring quarter, 2017,2018,2019,2020,2021,2022 winter quarter)
・Fundamental Physics IB (2014, 2015, 2016, 2017, 2018, 2019,2020, 2nd semester)
・Interdisciplinary Collaborative Learning of Social Issues A (2016 1st semester), (2014, 2015, 2016, 2017 2nd semester)
・Hands-on Natural Science (2017,2018 autumn&winter quarters)
・Seminar -- How to write clearly -- (2015, 1st semester)
・"Understanding" and "Easy to understand" (2018, 2019,2020,2021, autumn quarter)
・"Let's get hands on a math toolbox" (2021, 2022 summer quarter)

As for special sets of lectures:
・Introduction to Elementary Particle Physics (at Fukuoka University)
・Elementary Particles and Symmetries (at Fukuoka University)
・Nonrelativistic Scattering Theory (at Ehime University)
・Relativity (at Kagoshima University)
Other Educational Activities
  • 2010.03, Lectures at Shinshu Winter School 2010.
Professional and Outreach Activities
I participated in organizing a scientific event and delivered lectures to high school students at various high schools.By doing so, I have been trying to make people interested in science..