Keiichi NAGAOAssociate Professor
■Researcher basic information
Organization
- College of Education Training Course for School Teachers Program for Subject Education ／ Major in Science Education
- Graduate School of Education（Course for Professional degree ） Division of Professional Teacher Education Professional Course in School Subjects
- Faculty of Education Domain of Language, Social,& Natural Sciences
Research Areas
- Natural sciences, Mathematical physics and basic theory, 量子基礎論
- Natural sciences, Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics, Elementary Particle/Atomic Nucleus/Cosmic Ray/Space Physics
- Natural sciences, Applied mathematics and statistics
- Informatics, Mathematical informatics
- Humanities & social sciences, Science education, 物理教育 量子教育
Educational Background
- Apr. 1999 - Mar. 2002, The University of Tokyo, Graduate School of Arts and Sciences, Department of Multi-Disciplinary Sciences - Basic Science Doctor Course
- Apr. 1997 - Mar. 1999, The University of Tokyo, Graduate School of Arts and Sciences, Department of Multi-Disciplinary Sciences - Basic Science Master Course
- Apr. 1995 - Mar. 1997, The University of Tokyo, Faculty of Science, Department of Physics
Career
- Apr. 2007 - Present, Associate Professor, Department of Science Education, College of Education, Ibaraki University
- Nov. 2021 - Dec. 2022, Niels Bohr Institute, University of Copenhagen, Theoretical Particle Physics and Cosmology section, Guest Researcher
- Apr. 2008 - Sep. 2008, Niels Bohr Institute, University of Copenhagen, Theoretical Particle Physics and Cosmology section, Visiting Research Fellow
- Apr. 2005 - Mar. 2007, Department of Science Education, College of Education, Ibaraki University, Associate Professor
- Jan. 2003 - Mar. 2005, Institute of Particle and Nuclear Studies, ,High Energy Accelerator Research Organization (KEK), COE Fellow
- Apr. 2002 - Jan. 2003, Institute of Particle and Nuclear Studies, ,High Energy Accelerator Research Organization (KEK), Research Fellow
- Apr. 1999 - Mar. 2001, 東京大学教養学部, ティーチングアシスタント
Member History
- Apr. 2019 - Mar. 2021, 理科専修主任, 茨城大学大学院教育学研究科
- Apr. 2019 - Mar. 2021, 理科教育教室主任, 茨城大学教育学部
- Apr. 2019 - Mar. 2021, 理科教育推進事業 事業担当責任者（大学側）, 茨城大学・茨城県教育委員会
- Apr. 2017 - Mar. 2021, ボクシング部 顧問, 茨城大学
- Apr. 2018 - Mar. 2020, 臨床心理相談室運営委員会 委員, 茨城大学教育学部
- May 2018, 平成30年度 科学の甲子園ジュニア実行委員, 茨城県教育委員会
- Apr. 2015 - Mar. 2018, 宇宙科学教育研究センター運営委員会委員 委員, 茨城大学
- May 2017, 平成29年度 科学の甲子園ジュニア実行委員, 茨城県教育委員会
- Apr. 2011 - Mar. 2013, 宇宙科学教育研究センター運営委員会 委員, 茨城大学
- Apr. 2009 - Mar. 2013, プロレス研究会 顧問, 茨城大学
- Apr. 2011 - Mar. 2012, 教育実践総合センター協力委員会 紀要編集委員会 委員, 茨城大学教育学部
- Sep. 2004 - Sep. 2004, 2004年 秋季大会 座長（素粒子論28pSL）, 日本物理学会
- Dec. 2003 - Mar. 2004, KEK Theory Workshop '04 世話人, 高エネルギー加速器研究機構 素粒子原子核研究所 理論部
- Mar. 2000 - Mar. 2000, 2000年 春の分科会 座長（素粒子論31aSD）, 日本物理学会
- Aug. 1998 - Jul. 1999, '99 原子核三者若手 夏の学校 準備委員, 原子核三者若手
External link
■Research activity information
Paper
- Could random dynamics derive quantum mechanics via the weak value?
Holger Bech Nielsen; Keiichi Nagao, Last, University of Ljubljana, Faculty of Mathematics and Physics
Bled Workshops in Physics (Proceedings to the 27th workshop "What Comes Beyond the Standard Models", Bled, Slovenia, Jul.8-17, 2024), Dec. 2024, [Reviewed] - Automatic hermiticity for mixed states
Keiichi Nagao; Holger Bech Nielsen, Lead, We previously proposed a mechanism to effectively obtain, after a long time development, a Hamiltonian being Hermitian with regard to a modified inner product $I_Q$ that makes a given non-normal Hamiltonian normal by using an appropriately chosen Hermitian operator $Q$. ,We studied it for pure states. In this letter we show that a similar mechanism also works for mixed states by introducing density matrices to describe them and investigating their properties explicitly both in the future-not-included and future-included theories. ,In particular, in the latter, where not only a past state at the initial time $T_A$ but also a future state at the final time $T_B$ is given, we study a couple of candidates for it, and introduce a ``skew density matrix'' composed of both ensembles of the future and past states such that the trace of the product of it and an operator ${\cal O}$ matches a normalized matrix element of ${\cal O}$. ,We argue that the skew density matrix defined with $I_Q$ at the present time $t$ for large $T_B-t$ and large $t-T_A$ approximately corresponds to another density matrix composed of only an ensemble of past states and defined with ,another inner product $I_{Q_J}$ for large $t-T_A$., Oxford University Press (The Physical Society of Japan)
Progress of Theoretical and Experimental Physics, 16 Feb. 2023, [Reviewed] - What gives a “theory of Initial Conditions” ?
Holger Bech Nielsen; Keiichi Nagao, Last, The present work contains a review of some of the work we have done on ,complex action or non-Hermitian Hamiltonian theory, especially the result that the anti-Hermitian part of the Hamiltonian functions by determining the actual solution to the equations of motion, that should be realized; this means it predicts the initial conditions. It should be stressed that a major result of ours is that the effective equations of motion will in practice - after long time - be so accurately as if we had indeed a Hermitian Hamiltonian,,and so there is at first nothing wrong in assuming a non-Hermitian one. In fact it would practically seem Hermitian anyway. A major new point is that we seek by a bit intuitively arguing to suggest some cosmologically predictions from the mentioned initial conditions predicted: We seek even by assuming essentially nothing but very general properties of the non-Hermitian Hamiltonian that we in practice should find a bottom in the (effective Hermitian) Hamiltonian and that the Universe at some moment should pass through a (multiple) saddle point very closely, so that the time spent at it would be very long., DMFA
Bled Workshops in Physics ,(Proceedings to the 25th workshop "What Comes Beyond the Standard Models", Bled, Slovenia, Jul.4-10, 2022), Dec. 2022, [Reviewed] - Reality from maximizing overlap in the periodic complex action theory
Keiichi Nagao; Holger Bech Nielsen, Lead, Abstract
We study the periodic complex action theory (CAT) by imposing a periodic condition in the future-included CAT where the time integration is performed from the past to the future, and extend a normalized matrix element of an operator $\hat{\mathcal {O } }$, which is called weak value in the real action theory, to another expression $\langle \hat{\mathcal {O } } \rangle _{\mathrm{periodic}~\mathrm{time } }$. We present two theorems stating that $\langle \hat{\mathcal {O } } \rangle _{\mathrm{periodic}~\mathrm{time } }$ becomes real for $\hat{\mathcal {O } }$ being Hermitian with regard to a modified inner product that makes a given non-normal Hamiltonian $\hat{H}$ normal. The first theorem holds for a given period tp in a case where the number of eigenstates having the maximal imaginary part B of the eigenvalues of $\hat{H}$ is just one, while the second one stands for tp’s selected such that the absolute value of the transition amplitude is maximized in a case where B ≤ 0 and |B| is much smaller than the distances between any two real parts of the eigenvalues of $\hat{H}$. The latter proven via a number-theoretical argument suggests that, if our universe is periodic, then even the period could be an adjustment parameter to be determined in the Feynman path integral. This is a variant type of the maximization principle that we previously proposed., Oxford University Press (OUP)
Progress of Theoretical and Experimental Physics, 23 Jul. 2022, [Reviewed] - Formalism of a harmonic oscillator in the future-included complex action theory
Keiichi Nagao and Holger Bech Nielsen, Lead, In a special representation of complex action theory that we call ``future-included'', ,we study a harmonic oscillator model defined with a non-normal Hamiltonian $\hat{H}$, in which a mass $m$ and an angular frequency $\omega$ are taken to be complex numbers. In order for the model to be sensible some restrictions on $m$ and $\omega$ are required. We draw a phase diagram in the plane of the arguments of $m$ and $\omega$, according to which the model is classified into several types. ,In addition, we formulate two pairs of annihilation and creation operators, two series of eigenstates of the Hamiltonians $\hat{H}$ and $\hat{H}^\dag$, and coherent states. They are normalized in a modified inner product $I_Q$, with respect to which ,the Hamiltonian $\hat{H}$ becomes normal. Furthermore, applying to the model the maximization principle that we previously proposed, we obtain an effective theory described by a Hamiltonian that is $Q$-Hermitian, i.e. Hermitian with respect to the modified inner product $I_Q$. The generic solution to the model is found to be the ``ground'' state. Finally we discuss what the solution implies., Oxford University Press (The Physical Society of Japan)
Progress of Theoretical and Experimental Physics, 16 Jul. 2019, [Reviewed] - Erratum: ``Theory including future not excluded: Formulation of complex action theory II"
Keiichi Nagao; Holger Bech Nielsen, Lead, Oxford University Press (The Physical Society of Japan)
Progress of Theoretical and Experimental Physics, 27 Mar. 2018, [Reviewed] - Erratum: ``Momentum relation and classical limit in the future-not-included complex action theory"
Keiichi Nagao; Holger Bech Nielsen, Lead, Oxford University Press (The Physical Society of Japan)
Progress of Theoretical and Experimental Physics, 15 Feb. 2018, [Reviewed] - Reality from maximizing overlap in the future-included theories
Keiichi Nagao and Holger Bech Nielsen, Lead, In the future-included complex and real action ,theories whose paths run over not only the past but also the future, ,we briefly review the theorem on the normalized matrix element of an operator $\hat{\cal O}$, ,which is defined in terms of the future and past states ,with a proper inner product $I_Q$ that makes a given Hamiltonian normal. ,The theorem states that, ,provided that the operator $\hat{\cal O}$ is $Q$-Hermitian, i.e. ,Hermitian with regard to the proper inner product $I_Q$, ,the normalized matrix element ,becomes real and time-develops under ,a $Q$-Hermitian Hamiltonian ,for the past and future states selected such that ,the absolute value of the transition amplitude from ,the past state to the future state is maximized. ,Discussing what the theorem implicates, we speculate that ,the future-included complex action theory ,would be the most elegant quantum theory., DMFA
Bled Workshops in Physics ,(Proceedings to the 20th workshop "What Comes Beyond the Standard Models", Bled, Slovenia, Jul.9-17, 2017), 12 Dec. 2017, [Reviewed] - Momentum and Hamiltonian in complex action theory (vol 27, 1250076, 2012)
Keiichi Nagao; Holger Bech Nielsen, Lead, WORLD SCIENTIFIC PUBL CO PTE LTD
INTERNATIONAL JOURNAL OF MODERN PHYSICS A, Nov. 2017, [Reviewed] - Complex action suggests future-included theory
Keiichi Nagao; Holger Bech Nielsen, Lead, In quantum theory its action is usually taken to be real, but we can consider another theory whose action is complex. In addition, in the Feynman path integral, the time integration is usually performed over the period between the initial time T-A and some specific time, say, the present time t. Besides such a future-not-included theory, we can consider the future-included theory, in which not only the past state broken vertical bar A(T-A)) at the initial time T-A but also the future state broken vertical bar B(T-B)> at the final time T-B is given at first, and the time integration is performed over the whole period from the past to the future. Thus quantum theory can be classified into four types, according to whether its action is real or not, and whether the future is included or not. We argue that, if a theory is described with a complex action, then such a theory is suggested to be the future-included theory, rather than the future-not-included theory. Otherwise persons living at different times would see different histories of the universe., OXFORD UNIV PRESS INC
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, Nov. 2017, [Reviewed] - Reality from maximizing overlap in the future-included real action theory
Keiichi Nagao; Holger Bech Nielsen, Lead, In the future-included real action theory whose path runs over not only past but also future, we demonstrate a theorem, which states that the normalized matrix element of a Hermitian operator (O) over cap defined in terms of the future state at the final time T-B and the fixed past state at the initial time T-A becomes real for the future state selected such that the absolute value of the transition amplitude from the past state to the future state is maximized. This is a special version of our previously proposed theorem for the future-included complex action theory. We find that though the maximization principle leads to the reality of the normalized matrix element in the future-included real action theory, it does not specify the future and past states so much as in the case of the future-included complex action theory. In addition, we argue that the normalized matrix element seems to be more natural than the usual expectation value. Thus we speculate that the functional integral formalism of quantum theory could be most elegant in the future-included complex action theory., OXFORD UNIV PRESS INC
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, Aug. 2017, [Reviewed] - Reality and hermiticity from maximizing overlap in the future-included complex action theory
Keiichi Nagao; Holger Bech Nielsen, Lead, In the complex action theory whose path runs over not only past but also future, we study a normalized matrix element of an operator (O) over cap defined in terms of the future state at the latest time T-B and the past state at the earliest time T-A with a proper inner product that makes normal a given Hamiltonian that is non-normal at first. We present a theorem that states that, provided that the operator (O) over cap is Q-Hermitian, i.e., Hermitian with regard to the proper inner product, the normalized matrix element becomes real and time-develops under a Q-Hermitian Hamiltonian for the past and future states selected such that the absolute value of the transition amplitude from the past state to the future state is maximized. Furthermore, we give a possible procedure to formulate the Q-Hermitian Hamiltonian in terms of Q-Hermitian coordinate and momentum operators, and construct a conserved probability current density., OXFORD UNIV PRESS INC
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, May 2015, [Reviewed] - Momentum relation and classical limit in the future-not-included complex action theory
Keiichi Nagao; Holger Bech Nielsen, Lead, Studying the time development of the expectation value in the future-not-included complex action theory, we point out that the momentum relation (the relation analogous to p = partial derivative L/partial derivative q), which was derived via the Feynman path integral and was shown to be correct in the future-included theory in our previous papers, is not valid in the future-not-included theory. We provide the correct momentum relation in the future-not-included theory, and argue that the future-not-included classical theory is described by a certain real action. In addition, we provide anotherway to understand the time development of the future-not-included theory by utilizing the future-included theory. Furthermore, properly applying the method used in our previous paper to the future-not-included theory by introducing a formal Lagrangian, we derive the correct momentum relation in the future-not-included theory., OXFORD UNIV PRESS INC
PROGRESS OF THEORETICAL AND EXPERIMENTAL PHYSICS, Jul. 2013, [Reviewed] - Theory including future not excluded: Formulation of complex action theory II
Keiichi Nagao; Holger Bech Nielsen, Lead, We study a complex action theory (CAT) whose path runs over not only past but also future. We show that, if we regard a matrix element defined in terms of the future state at time TB and the past state at time TA as an expectation value in the CAT, then we are allowed to have the Heisenberg equation, Ehrenfest's theorem, and the conserved probability current density. In addition,we showthat the expectation value at the present time t of a future-included theory for large TB - t and large t - TA corresponds to that of a future-not-included theory with a proper inner product for large t - TA. Hence, the CAT with future explicitly present in the formalism and influencing in principle the past is not excluded phenomenologically, because the effects are argued to be very small in the present era. Furthermore, we explicitly derive the Hamiltonian for the future state via a path integral, and confirm that it is given by the Hermitian conjugate of the Hamiltonian for the past state. © The Author(s) 2013., Oxford University Press
Progress of Theoretical and Experimental Physics, 2013, [Reviewed] - Correspondence between future-included and future-not-included theories
Keiichi Nagao and Holger Bech Nielsen, Lead, We briefly review the correspondence principle proposed in our previous paper, which claims that if we regard a matrix element defined in terms of the future state at time $T_B$ and the past state at time $T_A$ as an expectation value in the complex action theory whose path runs over not only past but also future, the expectation value at the present time $t$ of a future-included theory for large $T_B-t$ and large $t-T_A$ corresponds to that of a future-not-included theory with a proper inner product for large $t-T_A$. This correspondence principle suggests that the future-included theory is not excluded phenomenologically.
Proceedings to the 15th workshop ``What Comes Beyond the Standard Models", Bled, Slovenia, Jul.9-19, 2012, Dec. 2012, [Reviewed] - Momentum and Hamiltonian in Complex Action Theory
Keiichi Nagao; Holger Bech Nielsen, Lead, In the complex action theory (CAT) we explicitly examine how the momentum and Hamiltonian are defined from the Feynman path integral (FPI) point of view based on the complex coordinate formalism of our foregoing paper. After reviewing the formalism briefly, we describe in FPI with a Lagrangian the time development of a xi-parametrized wave function, which is a solution to an eigenvalue problem of a momentum operator. Solving this eigenvalue problem, we derive the momentum and Hamiltonian. Oppositely, starting from the Hamiltonian we derive the Lagrangian in FPI, and we are led to the momentum relation again via the saddle point for p. This study confirms that the momentum and Hamiltonian in the CAT have the same forms as those in the real action theory. We also show the third derivation of the momentum relation via the saddle point for q., WORLD SCIENTIFIC PUBL CO PTE LTD
International Journal of Modern Physics A, Jun. 2012, [Reviewed] - Formulation of Complex Action Theory (vol 126, pg 1021, 2011)
Keiichi Nagao; Holger Bech Nielsen, Lead, PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
PROGRESS OF THEORETICAL PHYSICS, Jun. 2012, [Reviewed] - Formulation of Complex Action Theory
Keiichi Nagao; Holger Bech Nielsen, Lead, We formulate a complex action theory which includes operators of coordinate and momentum (q) over cap and (p) over cap being replaced with non-hermitian operators (q) over cap (new) and (p) over cap (new) and their eigenstates vertical bar q >(new) and vertical bar p >(new) with complex eigenvalues q and p. Introducing a philosophy of keeping the analyticity in path integration variables, we define a modified set of complex conjugate, real and imaginary parts, hermitian conjugates and bras, and explicitly construct (q) over cap (new), (p) over cap (new), vertical bar q >(new) and vertical bar p >(new) by formally squeezing coherent states. We also pose a theorem on the relation between functions on the phase space and the corresponding operators. Only in our formalism can we describe a complex action theory or a real action theory with complex saddle points in the tunneling effect etc. in terms of bras and kets in the functional integral. Furthermore, in a system with a non-hermitian diagonalizable bounded Hamiltonian, we show that the mechanism to obtain a hermitian Hamiltonian after a long time development proposed in our paper [Prog. Theor. Phys. 125 (2011), 633] works also in the complex coordinate formalism. If the hermitian Hamiltonian is given in a local form, a, conserved probability current density can be constructed with two kinds of wave functions., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
PROGRESS OF THEORETICAL PHYSICS, Dec. 2011, [Reviewed] - Automatic Hermiticity
Keiichi Nagao; Holger Bech Nielsen, Lead, We study a diagonalizable Hamiltonian that is not at first hermitian. Requirement that a measurement shall not change one Hamiltonian eigenstate into another one with a different eigenvalue imposes that an inner product must be defined so as to make the Hamiltonian normal with regard to it. After a long time development with the non-hermitian Hamiltonian, only a subspace of possible states will effectively survive. On this subspace the effect of the anti-hermitian part of the Hamiltonian is suppressed, and the Hamiltonian becomes hermitian. Thus hermiticity emerges automatically, and we have no reason to maintain that at the fundamental level the Hamiltonian should be hermitian. If the Hamiltonian is given in a local form, a conserved probability current density can be constructed with two kinds of wave functions. We also point out a possible misestimation of a past state by extrapolating back in time with the hermitian Hamiltonian. It is a seeming past state, not a true one., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
PROGRESS OF THEORETICAL PHYSICS, Mar. 2011, [Reviewed] - Complex Action Functioning as Cutoff and De Broglie-Bohm Particle
H.B.Nielsen; N.S.Mankoc Borstnik; K.Nagao; G.Moultaka, The purpose of this discussion contribution is to suggest the possibility that the imaginary action model could function as a cut off in loop diagrams. We argue also that the complex action model of M.Ninomiya and H.B.Nielsen has the De Broglie-Bohm particle appearing by itself, which is in a way already present in the contribution to this conference.
Proceedings to the 13th Workshop 'What Comes Beyond the Standard Models' Bled, July 12 - 22, 2010, Dec. 2010, [Reviewed], [Invited] - Erratum to: “Vortex fermion on the lattice” [Nucl. Phys. B 636 (2002) 264–290]
Keiichi Nagao
Nuclear Physics B, 03 Apr. 2008, [Reviewed] - Ginsparg-Wilson relation and admissibility condition in noncommutative geometry
Keiichi Nagao, Lead, Ginsparg-Wilson relation and admissibility condition have the key role to construct lattice chiral gauge theories. They are also useful to define the chiral structure in finite noncommutative geometries or matrix models. We discuss their usefulness briefly., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT, 2007, [Reviewed] - Dynamical aspects of the fuzzy CP2 in the large N reduced model with a cubic term
Takehiro Azuma; Subrata Bal; Keiichi Nagao; Jun Nishimura, "Fuzzy CP2", which is a four-dimensional fuzzy manifold analogous to the fuzzy 2-sphere (S-2), appears as a classical solution in the dimensionally reduced 8d Yang-Mills model with a cubic term involving the structure constant of the SU(3) Lie algebra. Although the fuzzy S-2, which is also a classical solution of the same model, has actually smaller free energy than the fuzzy CP2, Monte Carlo simulation shows that the fuzzy CP2 is stable even nonperturbatively due to the suppression of tunneling erects at large N as far as the coefficient of the cubic term (alpha) is sufficiently large. As alpha is decreased, both the fuzzy CP2 and the fuzzy S2 collapse to a solid ball and the system is essentially described by the pure Yang-Mills model (alpha = 0). The corresponding transitions are of first order. The gauge group generated dynamically above the critical point turns out to be of rank one for both CP2 and S2 cases. Above the critical point, we also perform perturbative calculations for various quantities to all orders, taking advantage of the one-loop saturation of the effective action in the large-N limit. By extrapolating our Monte Carlo results to N = infinity, we find excellent agreement with the all order results., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, May 2006, [Reviewed] - Admissibility condition and nontrivial indices on a noncommutative torus
Keiichi Nagao, We study the index of the Ginsparg-Wilson Dirac operator on a noncommutative torus numerically. To do this, we first formulate an admissibility condition which suppresses the fluctuation of gauge fields. Assuming this condition, we generate gauge configurations randomly, and find various configurations with nontrivial indices. We show one example of configurations with index 1 explicitly. This result provides the first evidence that nontrivial indices can be naturally defined on the noncommutative torus by utilizing the Ginsparg-Wilson relation and the admissibility condition., AMER PHYSICAL SOC
PHYSICAL REVIEW D, Mar. 2006, [Reviewed] - Topological aspects of gauge theory on noncommutative geometry
Hajime Aoki; J. Nishimura; Y. Susaki; S. Iso; T. Maeda; K. Nagao, American Physical Society
Annual Meeting of the Division of Particles and Fields of the American Physical Society, DPF 2006, and the Annual Fall Meeting of the Japan Particle Physics Community, 2006 - Perturbative versus nonperturbative dynamics of the fuzzy S-2 x S-2
T Azuma; S Bal; K Nagao; J Nishimura, We study a matrix model with a cubic term, which incorporates both the fuzzy S-2 x S-2 and the fuzzy S-2 as classical solutions. Both of the solutions decay into the vacuum of the pure Yang- Mills model (even in the large-N limit) when the coefficient of the cubic term is smaller than a critical value, but the large-N behavior of the critical point is different for the two solutions. The results above the critical point are nicely reproduced by the all order calculations in perturbation theory. By comparing the free energy, we find that the true vacuum is given either by the fuzzy S-2 or by the "pure Yang-Mills vacuum" depending on the coupling constant. In Monte Carlo simulation we do observe a decay of the fuzzy S-2 x S-2 into the fuzzy S-2 at moderate N, but the decay probability seems to be suppressed at large N. The above results, together with our previous results for the fuzzy CP2, reveal certain universality in the large-N dynamics of four-dimensional fuzzy manifolds realized in a matrix model with a cubic term., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, Sep. 2005, [Reviewed] - Impact of supersymmetry on the nonperturbative dynamics of fuzzy spheres
KN Anagnostopoulos; T Azuma; K Nagao; J Nishimura, We study a 4d supersymmetric matrix model with a cubic term, which incorporates fuzzy spheres as classical solutions, using Monte Carlo simulations and perturbative calculations. The fuzzy sphere in the supersymmetric model turns out to be always stable if the large-N limit is taken in such a way that various correlation functions scale. This is in striking contrast to analogous bosonic models, where the fuzzy sphere decays into the pure Yang-Mills vacuum due to quantum effects when the coeffcient of the cubic term becomes smaller than a critical value. We also find that the power-law tail of the eigenvalue distribution, which exists in the supersymmetric model without the cubic term, disappears in the presence of the fuzzy sphere in the large-N limit. Coincident fuzzy spheres turn out to be unstable, which implies that the dynamically generated gauge group is U(1)., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, Sep. 2005, [Reviewed] - Perturbative dynamics of fuzzy spheres at large N
T Azuma; K Nagao; J Nishimura, We clarify some peculiar aspects of the perturbative expansion around a classical fuzzy-sphere solution in matrix models with a cubic term. While the effective action in the large-N limit is saturated at the one-loop level, we find that the "one- loop dominance" does not hold for generic observables due to one-particle reducible diagrams. However, we may exploit the one-loop dominance for the effective action and obtain various observables to all orders from one-loop calculation by simply shifting the center of expansion to the "quantum solution", which extremizes the effective action. We confirm the validity of this method by comparison with the direct two-loop calculation and with Monte Carlo results in the 3d Yang-Mills-Chern-Simons matrix model. From the all order result we find that the perturbative expansion has a finite radius of convergence., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, Jun. 2005, [Reviewed] - Dynamical generation of a nontrivial index on the fuzzy 2-sphere
H Aoki; S Iso; T Maeda; K Nagao, Last, In the previous paper [H. Aoki, S. Iso, and K. Nagao, Nucl. Phys. B 684, 162 (2004)] we studied the 't Hooft-Polyakov (TP) monopole configuration in the U(2) gauge theory on the fuzzy 2-sphere and showed that it has a nonzero topological charge in the formalism based on the Ginsparg-Wilson relation. In this paper, by showing that the TP monopole configuration is stabler than the U(2) gauge theory without any condensation in the Yang-Mills-Chern-Simons matrix model, we will present a mechanism for dynamical generation of a nontrivial index. We further analyze the instability and decay processes of the U(2) gauge theory and the TP monopole configuration., AMERICAN PHYSICAL SOC
PHYSICAL REVIEW D, Feb. 2005, [Reviewed] - Absence of a fuzzy S-4 phase in the dimensionally reduced 5d Yang-Mills-Chern-Simons model
T Azuma; K Nagao; J Nishimura; S Bal, We perform nonperturbative studies of the dimensionally reduced 5d Yang-Mills-Chern-Simons model, in which a four-dimensional fuzzy manifold, "fuzzy S-4", is known to exist as a classical solution. Although the action is unbounded from below, a well-defined vacuum, which stabilizes at large N, exists when the coefficient of the Chern-Simons term is sufficiently small. However, this vacuum corresponds to the "Yang-Mills phase", in which the system behaves similarly to the pure Yang-Mills model. In Monte Carlo simulations we find that the fuzzy S-4 prepared as an initial configuration either diverges or falls into the Yang-Mills phase. Thus the model does not have a 'fuzzy S-4 phase" in contrast to our previous results on the dimensionally reduced 3d Yang-Mills-Chern-Simons model, in which the 'fuzzy S-2', can be realized dynamically., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, Jul. 2004, [Reviewed] - Nonperturbative studies of fuzzy spheres in a matrix model with the Chern-Simons term
T Azuma; S Bal; K Nagao; J Nishimura, Fuzzy spheres appear as classical solutions in a matrix model obtained via dimensional reduction of 3-dimensional Yang-Mills theory with the Chern-Simons term. Well-defined perturbative expansion around these solutions can be formulated even for finite matrix size, and in the case of k coincident fuzzy spheres it gives rise to a regularized U(k) gauge theory on a noncommutative geometry. Here we study the matrix model nonperturbatively by Monte Carlo simulation. The system undergoes a first order phase transition as we change the coefficient (alpha) of the Chern-Simons term. In the small alpha phase, the large-N properties of the system are qualitatively the same as in the pure Yang-Mills model (alpha=0), whereas in the large alpha phase a single fuzzy sphere emerges dynamically. Various 'multi fuzzy spheres' are observed as meta-stable states, and we argue in particular that the k coincident fuzzy spheres cannot be realized as the true vacuum in this model even in the large-N limit. We also perform one-loop calculations of various observables for arbitrary k including k=1. Comparison with our Monte Carlo data suggests that higher order corrections are suppressed in the large-N limit., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, May 2004, [Reviewed] - Ginsparg-Wilson relation and 't Hooft-Polyakov monopole on fuzzy 2-sphere
H Aoki; S Iso; K Nagao, Last, We investigate several properties of Ginsparg-Wilson fermion on fuzzy 2-sphere. We first examine chiral anomaly up to the second order of the gauge field and show that it is indeed reduced to the correct form of the Chern character in the commutative limit. Next we study topologically nontrivial gauge configurations and their topological charges. We investigate 't Hooft-Polyakov monopole type configuration on fuzzy 2-sphere and show that it has the correct commutative limit. We also consider more general configurations in our formulation. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV
NUCLEAR PHYSICS B, Apr. 2004, [Reviewed] - Matrix model and Ginsparg-Wilson relation
K Nagao, We discuss that the Ginsparg-Wilson relation, which has the key role in the recent development of constructing lattice chiral gauge theory, can play an important role to define chiral structures in finite matrix models and noncommutative geometries., ELSEVIER SCIENCE BV
NUCLEAR PHYSICS B-PROCEEDINGS SUPPLEMENTS, Mar. 2004, [Reviewed] - Chiral anomaly and Ginsparg-Wilson relation on the noncommutative torus
S Iso; K Nagao, Last, We evaluate chiral anomaly on the noncommutative torus with the overlap Dirac operator satisfying the Ginsparg-Wilson relation in arbitrary even dimensions. Utilizing a topological argument, we show that the chiral anomaly is combined into a form of the Chern character with star products., PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
PROGRESS OF THEORETICAL PHYSICS, Jun. 2003, [Reviewed] - Ginsparg-Wilson relation, topological invariants, and finite noncommutative geometry
Hajime Aoki; Satoshi Iso; Keiichi Nagao, Last, We show that the Ginsparg-Wilson (GW) relation can play an important role in defining chiral structures in finite noncommutative geometries. Employing the GW relation, we can prove the index theorem and construct topological invariants even if the system has only finite degrees of freedom. As an example, we consider a gauge theory on a fuzzy two-sphere and give an explicit construction of a noncommutative analogue of the GW relation, chirality operator, and the index theorem. The topological invariant is shown to coincide with the first Chern class in the commutative limit., AMER PHYSICAL SOC
PHYSICAL REVIEW D, Apr. 2003, [Reviewed] - Chiral anomaly on a fuzzy 2-sphere
H Aoki; S Iso; K Nagao, Last, We investigate the chiral anomaly for fermions in the fundamental representation on a noncommutative (fuzzy) 2-sphere. In spite of the fact that this system is realized by finite dimensional matrices and no regularization is necessary for either UV or IR, we can reproduce the correct chiral anomaly which is consistent with the calculations done in flat noncommutative space. As in the flat case, there are ambiguities in defining the chiral currents. We define the chiral currents in a gauge-invariant way and a gauge-covariant way, and show that the corresponding anomalous chiral Ward-Takahashi identities take different forms. The Ward-Takahashi identity for the gauge-invariant current contains explicit nonlocality while that for the covariant one is given by a local expression., AMER PHYSICAL SOC
PHYSICAL REVIEW D, Mar. 2003, [Reviewed] - Axial anomaly with the overlap-Dirac operator in arbitrary dimensions
T Fujiwara; K Nagao; H Suzuki, We evaluate for arbitrary even dimensions the classical continuum limit of the lattice axial anomaly defined by the overlap-Dirac operator. Our calculational scheme is simple and systematic. In particular, a powerful topological argument is utilized to determine the value of a lattice integral involved in the calculation. When the Dirac operator is free of species doubling, the classical continuum limit of the axial anomaly in various dimensions is combined into a form of the Chern character, as expected., SPRINGER
JOURNAL OF HIGH ENERGY PHYSICS, Sep. 2002, [Reviewed] - Vortex fermion on the lattice
Keiichi Nagao, The domain wall fermion formalism in lattice gauge theory is much investigated recently. This is set up by reducing (4 + 1)-dimensional theory to low energy effective 4-dimensional one. In order to look a-round other possibilities of realizing chiral fermion on the lattice, we construct vortex fermion by reducing (4 + 2)-dimensional theory to low energy effective 4-dimensional one on the lattice. In extra 2 dimensions we propose a new lattice regularization which has a discrete rotational invariance but not a translational one. In order to eliminate doubling species in the naive construction we introduce the extended Wilson term which is appropriate to our model. We propose two models for convenience and show that a normalizable zero mode solution appears at the core of the vortex. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
NUCLEAR PHYSICS B, Aug. 2002, [Reviewed] - Lattice QCD with the overlap fermions at strong gauge coupling (II)
Ikuo Ichinose; Keiichi Nagao, Last, In the previous paper we developed a strong-coupling expansion for the lattice QCD with the overlap fermions and showed that Luscher's "extended" chiral symmetry is spontaneously broken in some parameter region of the overlap fermions. In this paper, we derive a low-energy effective action of hadrons and show that there exist quasi-Nambu-Goldstone bosons which are identified as the pions. The pion field is a nonlocal composite field of quark and anti-quark even at the strong-coupling limit because of the nonlocality of the overlap fermion formalism and Luscher's chiral symmetry, The pions become massless in the limit of the vanishing bare-quark mass as it is desired. We furthermore examine symmetries of the overlap fermions with the hopping expansion and argue that there appear no other massless modes other than the pions. (C) 2001 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
NUCLEAR PHYSICS B, Feb. 2001, [Reviewed] - Lattice QCD with the overlap fermions at strong gauge coupling
Ikuo Ichinose; Keiichi Nagao, Last, We generalize overlap fermion by Narayanan and Neuberger by introducing a hopping parameter t. This lattice fermion has desirable properties as the original overlap fermion. We expand "Dirac" operator of this fermion in powers of t. Higher-order terms of t are long-distance terms and this t-expansion is a kind of the hopping expansion. It is shown that the Ginsparg-Wilson relation is satisfied at each order of t. We show that this t-expansion is useful for study of the strong-coupling gauge theory. We apply this formalism to the lattice QCD and study its chiral phase structure at strong coupling. We find that there are (at least) two phases one of which has desired chiral properties of QCD. Possible phase structure of the lattice QCD with the overlap fermions is proposed. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
NUCLEAR PHYSICS B, Jun. 2000, [Reviewed] - Gauged Gross-Neveu model with overlap fermions
Ikuo Ichinose; Keiichi Nagao, Last, We investigate chiral properties of the overlap lattice fermion by using solvable model in two dimensions, the gauged Gross-Neveu model. In this model, the chiral symmetry is spontaneously broken in the presence of small but finite fermion mass. We calculate the quasi-Nambu-Goldstone(NG) boson mass as a function of the bare fermion mass and two parameters in the overlap formula. We find that the quasi-NC boson mass has desired properties as a result of the extended chiral symmetry found by Luscher. We also show the PCAC relation is satisfied in desired form. Comparison between the overlap and Wilson lattice fermions is also made., PHYSICAL SOC REPUBLIC CHINA
CHINESE JOURNAL OF PHYSICS, Jun. 2000, [Reviewed] - Gross-Neveu model with overlap fermions
Ikuo Ichinose; Keiichi Nagao, Last, We investigate the chiral properties of overlap lattice fermion by using two-dimensional Gross-Neveu model coupled with a gauge field. Chiral properties of this model are similar to those of QCD(4), i.e. the chiral symmetry is spontaneously broken in the presence of small but finite fermion mass and also there appears the chiral anomaly because of the coupling with the gauge field. To take into consideration Luscher's extended chiral symmetry, we insert overlap Dirac operator even in the interaction terms so that the whole action including them are invariant under the extended chiral transformation at finite lattice spacing though the interaction terms become nonlocal. We calculate mass of the quasi-Namb-Goldstone boson as a function of the bare fermion mass and two parameters in the overlap formalism and find that the quasi-Nambu-Goldstone boson has desired properties as a result of the extended chiral symmetry. Furthermore we examine the PCAC relation and find that it is satisfied at finite lattice spacing. Relationship between the anomaly term in the PCAC relation and the U(1) problem is also discussed., WORLD SCIENTIFIC PUBL CO PTE LTD
MODERN PHYSICS LETTERS A, Apr. 2000, [Reviewed] - Pion mass and the PCAC relation in the overlap fermion formalism: Gauged Gross-Neveu model on a lattice
Ikuo Ichinose; Keiichi Nagao, Last, We investigate chiral properties of the overlap lattice fermion by using solvable model in two dimensions, the gauged Gross-Neveu model. Ln this model, the chiral symmetry is spontaneously broken in the presence of small but finite fermion mass. We calculate the quasi-Nambu-Goldstone (NG) boson mass as a function of the bare fermion mass a-nd two parameters in the overlap formula. We find that the quasi-NC boson mass has desired properties as a result of the extended chiral symmetry found by Luscher. We also examine the PCAC relation and find that it is satisfied in the continuum limit. Comparison between the overlap and Wilson lattice fermions is made. (C) 1999 Published by Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV
PHYSICS LETTERS B, Aug. 1999, [Reviewed]
MISC
- The current status and issues of experiments on “the properties of electromagnets” in elementary school science
Keiichi Nagao
茨城大学教育学部紀要（教育科学）, 30 Jan. 2018 - Automatic Hermiticity
永尾 敬一
素粒子論研究・電子版, 02 Dec. 2012 - An inquiry into the reproduction of physics-phobic children by physics-phobic teachers
Takehiro Azuma; Keiichi Nagao
arXiv:0803.3167v2 [physics.ed-ph], 24 Mar. 2008
Last - An inquiry into the reproduction of physics-phobic children by physics-phobic teachers
Takehiro Azuma; Keiichi Nagao
Bulletin of the Faculty of Education Ibaraki University (Educational Sciences), 10 Sep. 2007
Last - Perturbative versus nonperturbative dynamics of the fuzzy S^2×S^2
永尾 敬一
Soryushiron Kenkyu, 20 Jan. 2006 - Nonperturbative studies of the 4d supersymmetric reduced model with the Chern-Simons term
永尾 敬一
素粒子論研究, 20 Dec. 2004 - Ginsparg-Wilson Relation, Topological Invariants and Finite Noncommutative Geometry
永尾 敬一
素粒子論研究, 20 Jun. 2004 - Chiral anomaly and Ginsparg-Wilson relation on the noncommutative torus
永尾 敬一
素粒子論研究, 2003 - Dirac Operator and Chiral Anomaly on Fuzzy 2-Sphere
永尾 敬一
数理物理2002, Sep. 2002 - 格子ゲージ理論におけるvortex fermionの構成
永尾 敬一
素粒子論研究, Jul. 2002 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Ikuo Ichinose; Keiichi Nagao
Tokutei Ryouiki Kenkyu (B)707 "Supersymmetry", Feb. 2000
Last - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged Gross-Neveu Model on a Lattice
一瀬 郁夫; 永尾 敬一
素粒子論研究, Jan. 2000
Last
Books and other publications
- Future-included complex action theory : Toward deeper understanding of quantum theory
Keiichi Nagao; Holger Bech Nielsen, Contributor
茨城大学教育学部出版会, 31 Mar. 2025
9784991421501 - Fundamentals of Quantum Complex Action Theory
Keiichi Nagao; Holger Bech Nielsen, Joint work
Lambert Academic Publishing, 27 Sep. 2017, [Reviewed]
9783330084452 - Gerda Steiner & Jörg Lenzlinger - power sources
門脇さや子編, Joint translation
水戸芸術館現代美術センター, 31 Mar. 2012
9784943825982 - 理科実験大百科 第10集
Keiichi Nagao, Contributor
少年写真新聞社, Feb. 2010
9784879813312 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Ikuo Ichinose; Keiichi Nagao, Contributor
Dynamics of gauge fields: TMU-Yale Symposium, May 2000, [Reviewed]
9784946443589
Lectures, oral presentations, etc.
- Complex action suggests future-included theory
永尾 敬一、Holger Bech Nielsen
日本物理学会2024年春季大会, 19 Mar. 2024, 日本物理学会
20240318, 20240321 - Reality from maximizing overlap in the periodic complex action theory
永尾 敬一、Holger Bech Nielsen
日本物理学会2024年春季大会, 19 Mar. 2024, 日本物理学会
20240318, 20240321 - Automatic hermiticity for mixed states
永尾 敬一、Holger Bech Nielsen
日本物理学会2024年春季大会, 19 Mar. 2024, 日本物理学会
20240318, 20240321 - Automatic hermiticity for mixed states
Keiichi Nagao
KEK Theory Workshop 2023, 30 Nov. 2023, KEK (High Energy Accelerator Research Organization) Thory Center
20231129, 20231201 - Reality from maximizing overlap in the periodic complex action theory
Keiichi Nagao
KEK Theory Workshop 2022, 08 Dec. 2022, KEK (High Energy Accelerator Research Organization) Thory Center
20221207, 20221209 - Reality from maximizing overlap in the periodic complex action theory
Keiichi Nagao
Joint Theory Seminar @NBI, 13 Oct. 2022, Theoretical particle physics and cosmology group, Niels Bohr Institute, [Invited]
20221013, 20221013 - Formalism of harmonic oscillator in the future-included complex action theory
Keiichi Nagao
Theoretical High Energy Seminar @NBI, 12 Feb. 2019, Theoretical particle physics and cosmology group, Niels Bohr Institute, [Invited]
20190212, 20190212 - Reality from maximizing overlap in the future-included real action theory
永尾 敬一; Holger Bech Nielsen
日本物理学会2017年秋季大会, 12 Sep. 2017, 日本物理学会 - Reality from maximizing overlap in the future-included real action theory
Keiichi Nagao
茨城大学理学部素粒子論研究室セミナー, 12 Jun. 2017, 茨城大学理学部素粒子論研究室, [Invited] - Reality and hermiticity from maximizing overlap in the future-included complex action theory
Keiichi Nagao
Theoretical High Energy Seminar @NBI, 09 Feb. 2017, Theoretical particle physics and cosmology group, Niels Bohr Institute, [Invited]
20170209, 20170209 - Reality and hermiticity from maximizing overlap in the future-included complex action theory
永尾 敬一; Holger Bech Nielsen
日本物理学会2015年秋季大会, 16 Sep. 2015, 日本物理学会 - Expression of the Q operator for the proper inner product in complex harmonic oscillator
永尾 敬一; Holger Bech Nielsen
日本物理学会2015年秋季大会, 16 Sep. 2015, 日本物理学会 - Reality and hermiticity from maximizing overlap in the future-included complex action theory
永尾 敬一
日本大学理工学部素粒子論研究室セミナー, 24 Jun. 2015, 日本大学理工学部素粒子論研究室, [Invited] - Reality and hermiticity from maximizing overlap in the future-included complex action theory
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 18 May 2015, 茨城大学理学部素粒子論研究室, [Invited] - Momentum relation and classical limit in the future-not-included complex action theory
永尾 敬一; Holger Bech Nielsen
日本物理学会2015年年次大会, 22 Mar. 2015, 日本物理学会 - Momentum relation and classical limit in the future-not-included complex action theory
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 19 May 2014, 茨城大学理学部素粒子論研究室, [Invited] - Momentum relation and classical limit in the future-not-included complex action theory
永尾 敬一
QMKEK2014 量子論の諸問題と今後の発展, 11 Mar. 2014, 高エネルギー加速器研究機構（KEK） - Momentum relation and classical limit in the future-not- included complex action theory
Keiichi Nagao
中部夏の学校２０１３, 01 Sep. 2013 - Momentum relation and classical limit in the future-not-included complex action theory
Keiichi Nagao
基研研究会 素粒子物理学の進展２０１３, 07 Aug. 2013 - Theory Including Future Not Excluded
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 22 Apr. 2013, 茨城大学理学部素粒子論研究室, [Invited] - Theory Including Future Not Excluded
Keiichi Nagao
KEK理論研究会2013, 19 Mar. 2013, 高エネルギー加速器研究機構(KEK) - Theory Including Future Not Excluded
永尾 敬一
京都大学理学部 素粒子論研究室セミナー, 27 Feb. 2013, 京都大学理学部 素粒子論研究室, [Invited] - Theory Including Future Not Excluded
Keiichi Nagao and Holger Bech Nielsen
日本物理学会2012年秋季大会, 11 Sep. 2012, 日本物理学会 - Formulation of complex action theory
Keiichi Nagao
Seminar @RBI, 20 Jul. 2012, [Invited]
20120720, 20120720 - Formulation of complex action theory
Keiichi Nagao
Bled 2012: What comes Beyond the Standard Models, 10 Jul. 2012, [Invited] - Momentum and Hamiltonian in Complex Action Theory
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 18 Jun. 2012, 茨城大学理学部素粒子論研究室, [Invited] - Formulation of Complex Action Theory
Keiichi Nagao
東北大学理学部素粒子論研究室セミナー, 10 May 2012, 東北大学理学部素粒子論研究室, [Invited] - Formulation of Complex Action Theory
Keiichi Nagao
QMKEK2012 量子論の諸問題と今後の発展, 17 Mar. 2012, 高エネルギー加速器研究機構（KEK） - Formulation of Complex Action Theory
Keiichi Nagao
KEK理論研究会2012, 06 Mar. 2012, 高エネルギー加速器研究機構（KEK） - Automatic Hermiticity
Keiichi Nagao
京都大学基礎物理学研究所研究会「物理と情報の階層構造 ―情報を接点とした諸階層の制御と創発―」, 07 Jan. 2012, 京都大学基礎物理学研究所 - Formulation of Complex Action Theory
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 12 Dec. 2011, 茨城大学理学部素粒子論研究室, [Invited] - Automatic Hermiticity
Keiichi Nagao and Holger Bech Nielsen
日本物理学会2011年秋季大会, 18 Sep. 2011, 日本物理学会 - Formulation of Complex Action Theory
Keiichi Nagao and Holger Bech Nielsen
日本物理学会2011年秋季大会, 18 Sep. 2011, 日本物理学会 - Momentum and Hamiltonian in Complex Action Theory
Keiichi Nagao and Holger Bech Nielsen
日本物理学会2011年秋季大会, 18 Sep. 2011, 日本物理学会 - Automatic Hermiticity
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 09 May 2011, 茨城大学理学部素粒子論研究室, [Invited] - Automatic Hermiticity
Keiichi Nagao
KEK理論研究会2011, 15 Mar. 2011, 高エネルギー加速器研究機構（KEK） - Automatic Hermiticity
Keiichi Nagao
Theoretical High Energy Seminar @NBI, 03 Feb. 2011, [Invited] - Ginsparg-Wilson Relation and Admissibility Condition in Noncommutative Geometry
Keiichi Nagao
Noncommutative Geometry and Quantum Spacetime in Physics,21st Nishinomiya-Yukawa Memorial Symposium on Theoretical Physics, 14 Nov. 2006, Yukawa Institute for Theoretical Physics and the Grant-in-Aid for the 21st Century COE (Kyoto U.) "Center for Diversity and Universality in Physics" - Matrix Model and Ginsparg-Wilson Relation
永尾 敬一
茨城大学理学部素粒子論研究室セミナー, 14 Nov. 2005, 茨城大学理学部素粒子論研究室, [Invited] - Perturbative versus nonperturbative dynamics of the fuzzy S2×S2
Keiichi Nagao
基研研究会「弦理論、場の量子論の展望」, 21 Aug. 2005, 京都大学基礎物理学研究所 - Nonperturbative Studies of Fuzzy Spheres in Matrix Models
Keiichi Nagao
基研研究会「格子ゲージ理論の新しい芽と発展」, 09 Dec. 2004, 京都大学基礎物理学研究所 - 一般化されたGinsparg-Wilson 関係式と非可換幾何
永尾 敬一
日本物理学会2004年秋季大会, 28 Sep. 2004, 日本物理学会
20040927, 20040930 - S2 × S2 versus S2 : which one is the true vacuum of the 6d Yang-Mills-Chern-Simons Matrix Model?
東 武大、Subrata Bal(登壇者)、永尾 敬一、西村 淳
日本物理学会2004年秋季大会, 28 Sep. 2004, 日本物理学会
20040927, 20040930 - Monte-Carlo studies of the 4d supersymmetric reduced model with the Chern-Simons term
Konstantinos N. Anagnostopoulos、東 武大(登壇者)、永尾 敬一、西村 淳
日本物理学会2004年秋季大会, 28 Sep. 2004, 日本物理学会
20040927, 20040930 - Dynamical aspects of the fuzzy CP2 in the large N reduced model with a cubic term
東 武大、Subrata Bal、永尾 敬一(登壇者)、西村 淳、
日本物理学会2004年秋季大会, 28 Sep. 2004, 日本物理学会
20040927, 20040930 - Dynamical Aspects of Fuzzy Sphers in Matrix Models
永尾 敬一
中部夏の学校, 30 Aug. 2004
20040828, 20040831 - Nonperturbative studies of the 4d supersymmetric reduced model with the Chern-Simons term
Keiichi Nagao
基研研究会「場の量子論2004」, 14 Jul. 2004, 京都大学基礎物理学研究所 - Matrix Model and Ginsparg-Wison Relation
Keiichi Nagao
Fuzzy Physics 2004, 17 Jun. 2004, Cinvestav, the Center for Research and Advanced Studies of the National Polytechnic Institute, [Invited] - Nonperturbative Dynamics of Fuzzy Spheres in Matrix Models
Keiichi Nagao
Fuzzy Physics 2004, 16 Jun. 2004, Cinvestav, the Center for Research and Advanced Studies of the National Polytechnic Institute, [Invited] - Nonperturbative studies of higher-dimensional fuzzy-spheres in the matrix model
東 武大(登壇者)、Subrata Bal、永尾 敬一、西村 淳
日本物理学会2004年年次大会, 30 Mar. 2004, 日本物理学会
20040327, 20040330 - Dynamical generation of gauge group in matrix models
東 武大、Subrata Bal、永尾 敬一(登壇者)、西村 淳
日本物理学会2004年年次大会, 28 Mar. 2004, 日本物理学会
20040327, 20040330 - Nonperturbative dynamics of fuzzy spheres in matrix models
Keiichi Nagao
KEK Theory Workshop 2004, 16 Mar. 2004, 高エネルギー加速器研究機構, [Invited]
20040316, 20040318 - Nonperturbative Studies of Fuzzy Spheres and Ginsparg-Wilson Fermion in Matrix Models
Keiichi Nagao
大阪大学素粒子論研究室セミナー, 10 Feb. 2004, [Invited] - Ginsparg-Wilson Relation and 't Hooft-Polyakov Monopole on Fuzzy 2-Sphere
Keiichi Nagao
Sapporo Winter School in Niseko '04, 09 Jan. 2004, 北海道大学 素粒子論研究室
20040108, 20040112 - Nonperturbative Studies of the Fuzzy Sphere in a Matrix Model with the Chern-Simons Term
Keiichi Nagao
茨城大学素粒子論研究室セミナー, 08 Dec. 2003, [Invited] - Nonperturbative Studies of the Fuzzy Sphere in a Matrix Model with the Chern-Simons Term
Keiichi Nagao
日本大学素粒子論研究室セミナー, 03 Dec. 2003, [Invited] - Topological Invariants on the Noncommutative Torus
永尾敬一
日本物理学会2003年秋季大会, 10 Sep. 2003, 日本物理学会
20030909, 20030912 - Axial anomaly with the overlap-Dirac operator in arbitrary dimensions
藤原 高徳、永尾 敬一(登壇者)、鈴木 博
日本物理学会2003年秋季大会, 10 Sep. 2003, 日本物理学会
20030909, 20030912 - Chiral Anomaly and Ginsparg-Wilson Relation on the Noncommutative Torus
磯 暁、永尾 敬一(登壇者)
日本物理学会2003年秋季大会, 10 Sep. 2003, 日本物理学会
20030909, 20030912 - Nonperturbative stability of the fuzzy sphere in a matrix model with the Chern-Simons term
東 武大(登壇者)、Subrata Bal、永尾 敬一、西村 淳
日本物理学会2003年秋季大会, 09 Sep. 2003, 日本物理学会
20030909, 20030912 - Chiral Anomaly and Ginsparg-Wilson Relation on the Noncommutative Torus
Keiichi Nagao
基研研究会「場の量子論2003」, 05 Aug. 2003, 京都大学基礎物理学研究所 - Chiral Anomaly and Ginsparg-Wilson Relation on the Noncommutative Torus
Keiichi Nagao
東京都立大学 素粒子論研究室セミナー, 04 Jun. 2003, [Invited] - 行列模型とGinsparg-Wilson 関係式
青木 一、磯 暁、永尾 敬一(登壇者)
日本物理学会2003年年次大会, 28 Mar. 2003, 日本物理学会
20030328, 20030331 - Ginsparg-Wilson Relation, Topological Invariants and Finite Noncommutative Geometry
永尾 敬一
基研研究会「格子場の理論スクール」, 22 Oct. 2002, 京都大学基礎物理学研究所
20021021, 20021025 - Dirac Oprator and Chiral Anomaly on Fuzzy 2-Sphere
永尾 敬一
数理物理2002「非可換幾何と数理物理」, 22 Sep. 2002, 東京大学数理科学研究科
20020921, 20020923 - 2次元非可換球面上でのDirac operator とカイラルアノマリー
青木 一、磯 暁、永尾 敬一(登壇者)
日本物理学会2002年秋季大会, 13 Sep. 2002, 日本物理学会
20020913, 20020916 - 2次元非可換球面上でのDirac operatorとカイラルアノマリー
Keiichi Nagao
基研研究会「場の量子論2002」, 24 Jul. 2002, 京都大学基礎物理学研究所 - Vortex Fermion on the Lattice
Keiichi Nagao
筑波大学素粒子論研究室セミナー, 01 Mar. 2002, [Invited] - Vortex Fermion on the Lattice
Keiichi Nagao
高エネルギー加速器研究機構 素粒子原子核研究所理論部セミナー, Feb. 2002, [Invited] - Vortex Fermion on the Lattice
Keiichi Nagao
Sapporo Winter School 2002, 10 Jan. 2002, 北海道大学 素粒子論研究室
20020109, 20020111 - Vortex fermion on the lattice
Keiichi Nagao
基研研究会「場の量子論の基礎的諸問題と応用」, 20 Dec. 2001, 京都大学基礎物理学研究所
20011219, 20011221 - 格子ゲージ理論におけるvortex fermion の構成
永尾敬一
日本物理学会2001年秋季大会, 22 Sep. 2001, 日本物理学会
20010922, 20010925 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling (II)
一瀬 郁夫、永尾 敬一(登壇者)
日本物理学会2001年年次大会, 27 Mar. 2001, 日本物理学会
20010327, 20010330 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling (II)
Keiichi Nagao
Sapporo Winter School in Niseko '01, 09 Jan. 2001, 北海道大学 素粒子論研究室
20010107, 20010111 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Keiichi Nagao
日本大学素粒子論研究室セミナー, 08 Nov. 2000, [Invited] - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
一瀬 郁夫、永尾 敬一(登壇者)
日本物理学会2000年春の分科会, 31 Mar. 2000, 日本物理学会
20000330, 20000402 - New approach to approximate solutions of Ginsparg-Wilson relation and its applications
永尾 敬一
格子上のカイラル対称性に関する最近の進展, 09 Mar. 2000
20000308, 20000309 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Keiichi Nagao
Sapporo Winter School in Niseko '00, 04 Mar. 2000, 北海道大学 素粒子論研究室
20000302, 20000306 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Ikuo Ichinose; Keiichi Nagao
Dynamics of Gauge Fields: TMU-Yale Symposium, 14 Dec. 1999
19991213, 19991215 - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged Gross-Neveu Model on a Lattice
Keiichi Nagao
東京都立大学素粒子論研究室セミナー, 01 Dec. 1999, [Invited] - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Keiichi Nagao
SUCAL99「超対称性、カイラル対称性と格子ゲージ理論」, 18 Nov. 1999
19991117, 19991119 - Lattice QCD with the Overlap Fermions at Strong Gauge Coupling
Keiichi Nagao
東京大学駒場素粒子論研究室セミナー, 10 Nov. 1999 - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged Gross-Neveu Model on a Lattice
Keiichi Nagao
中央大学素粒子論研究室セミナー, 05 Oct. 1999, [Invited] - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged,Gross-Neveu Model on a Lattice
一瀬 郁夫、永尾 敬一(登壇者)
日本物理学会1999年秋の分科会, 23 Sep. 1999, 日本物理学会
19990923, 19990926 - Gauged Gross-Neveu model with Overlap Fermions
Ikuo Ichinose; Keiichi Nagao(speaker)
Chiral '99, Sep. 1999, National Taiwan University
199909, 199909 - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged Gross-Neveu Model on a Lattice
永尾 敬一
中部夏の学校, 23 Aug. 1999
19990823, 19990825 - Pion Mass and the PCAC Relation in the Overlap Fermion Formalism: Gauged Gross-Neveu Model on a Lattice
Keiichi Nagao
基研研究会「場の量子論と弦理論の新しい展開」, 30 Jul. 1999, 京都大学基礎物理学研究所 - Theoreical Particle Physics
Keiichi Nagao
JAMS '97, Aug. 1997, 財団法人数理科学振興会, [Invited]
199708, 199708
Courses
Affiliated academic society
Research Themes
- 複素作用理論及びインフレーション宇宙論における自然性問題の研究
Grant-in-Aid for Scientific Research (C)
Ibaraki University
Apr. 2021 - Mar. 2026 - 未来を含む複素作用理論
Aug. 2024 - Feb. 2025 - 高度な数学を使わない量子教育に関する研究
Aug. 2023 - Mar. 2024 - Complex Action Theory
Jul. 2022 - Mar. 2023 - 複素作用理論の研究
Sep. 2021 - Mar. 2022 - 複素作用理論の研究
Sep. 2020 - Mar. 2021 - Complex Action Theory
Sep. 2019 - Mar. 2020 - 複素作用理論の基礎的研究およびその宇宙論への応用
Jun. 2013 - Mar. 2014 - 複素作用理論の基礎的研究およびその宇宙論への応用
Jul. 2012 - Mar. 2013 - 量子重力理論の一般的問題と非摂動論的かつ背景独立な定式化の研究
Grant-in-Aid for Young Scientists(B)
Ibaraki University
Apr. 2009 - Mar. 2013 - 複素作用理論の基礎的研究およびその宇宙論への応用
Jul. 2011 - Mar. 2012 - 超弦理論および量子重力理論の非摂動論的定式化に関する研究
Grant-in-Aid for Young Scientists(B)
Ibaraki University
Apr. 2006 - Mar. 2009 - 背景独立な行列模型およびループ重力におけるカイラルフェルミオンの定式化の研究
特定国派遣研究者（デンマーク）
コペンハーゲン大学 ニールス・ボーア研究所
Apr. 2008 - Sep. 2008
Social Contribution Activities
- R6年度茨城大学高大連携事業
lecturer
茨城大学, 模擬授業「物理学概論」のスタンバイ, 01 Apr. 2024 - 31 Mar. 2025 - R6年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Apr. 2024 - 31 Jul. 2024 - R6年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Apr. 2024 - 31 Jul. 2024 - R5年度茨城大学高大連携事業
lecturer
茨城大学, 模擬授業「物理学概論」のスタンバイ, 01 Apr. 2023 - 31 Mar. 2024 - R5年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Apr. 2023 - 11 May 2023 - R5年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Apr. 2023 - 11 May 2023 - R4年度茨城大学高大連携事業
lecturer
茨城大学, 模擬授業「物理学概論」のスタンバイ, 01 Apr. 2022 - 31 Mar. 2023 - R4年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Dec. 2022 - 31 Jan. 2023 - R4年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Dec. 2022 - 31 Jan. 2023 - R3年度茨城大学高大連携事業
lecturer
茨城大学, 模擬授業「物理学概論」のスタンバイ, 01 Apr. 2021 - 31 Mar. 2022 - R3年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Apr. 2021 - 31 May 2021 - R3年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Apr. 2021 - 31 May 2021 - R2年度茨城大学高大連携事業
lecturer
茨城大学, 模擬授業「物理学概論」のスタンバイ, 01 Apr. 2020 - 31 Mar. 2021 - R2年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Apr. 2020 - 31 Jul. 2020 - R2年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Apr. 2020 - 31 Jul. 2020 - 令和二年度いばらき理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠オンライン
lecturer
21 Jul. 2020 - 21 Jul. 2020 - R元年度茨城大学高大連携事業
lecturer
模擬授業「物理学概論」のスタンバイ, 01 Apr. 2019 - 31 Mar. 2020 - 令和元年度いばらき理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
31 Jul. 2019 - 31 Jul. 2019 - R元年度 水戸メディカルカレッジ 理学療法学科 講師
lecturer
01 Apr. 2019 - 31 Jul. 2019 - R元年度 水戸メディカルカレッジ 看護学科 講師
lecturer
01 Apr. 2019 - 31 Jul. 2019 - 令和元年度教員免許状更新講習・新展開講習（理科・農業）「量子論入門」
lecturer
16 Jun. 2019 - 16 Jun. 2019 - 令和元年度教員免許状更新講習・新展開講習（理科・農業）「素粒子論入門」
lecturer
16 Jun. 2019 - 16 Jun. 2019 - 令和元年度科学の甲子園ジュニア茨城県大会の問題についての助言と指導
advisor
茨城県教育委員会, 22 May 2019 - 22 May 2019 - 高校生を対象とした研究室見学会
lecturer
30 Mar. 2019 - 30 Mar. 2019 - 平成３０年度教員免許状更新講習・新展開講習（理科・農業）「量子論入門」（午前の部）
lecturer
29 Aug. 2018 - 29 Aug. 2018 - 平成３０年度教員免許状更新講習・新展開講習（理科・農業）「量子論入門」（午後の部）
lecturer
29 Aug. 2018 - 29 Aug. 2018 - 平成30年度科学の甲子園ジュニア茨城県大会の運営についての助言
advisor
茨城県教育委員会, 25 Aug. 2018 - 25 Aug. 2018 - 平成３０年度いばらき理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
31 Jul. 2018 - 31 Jul. 2018 - 平成30年度科学の甲子園ジュニア茨城県大会の問題についての助言と指導
advisor
茨城県教育委員会, 06 Jun. 2018 - 06 Jun. 2018 - 平成２９年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠鉾田市立鉾田小学校
lecturer
26 Oct. 2017 - 26 Oct. 2017 - 平成２９年度小学校理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
31 Jul. 2017 - 31 Jul. 2017 - 平成２９年度科学の甲子園ジュニア茨城県大会の問題についての助言と指導
advisor
茨城県教育委員会, Jun. 2017 - Jun. 2017 - 平成２８年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠鹿嶋市立中野西小学校
lecturer
15 Nov. 2016 - 15 Nov. 2016 - 平成２８年度いばらき理科教育推進事業「科学自由研究の指導(活用・発展)」ミニ博士によるミニ学会＠ミュージアムパーク茨城県自然博物館
lecturer
23 Oct. 2016 - 23 Oct. 2016 - 平成２８年度小学校理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
01 Aug. 2016 - 01 Aug. 2016 - 平成２７年度いばらき理科教育推進事業「科学自由研究の指導(活用・発展)」ミニ博士によるミニ学会＠ミュージアムパーク茨城県自然博物館
lecturer
25 Oct. 2015 - 25 Oct. 2015 - 平成２７年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠常陸太田市立太田小学校
lecturer
07 Oct. 2015 - 07 Oct. 2015 - 平成２７年度小学校理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
30 Jul. 2015 - 30 Jul. 2015 - 平成２６年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠土浦市立都和南小学校
lecturer
28 Nov. 2014 - 28 Nov. 2014 - 平成２６年度いばらき理科教育推進事業「科学自由研究の指導(活用・発展)」ミニ博士によるミニ学会＠ミュージアムパーク茨城県自然博物館
lecturer
26 Oct. 2014 - 26 Oct. 2014 - 平成２６年度小学校理科教育推進事業「科学自由研究の指導(探究基礎)」夏休み科学自由研究相談会＠茨城県女性プラザ
lecturer
31 Jul. 2014 - 31 Jul. 2014 - 平成２５年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠小美玉市立野田小学校
lecturer
28 Nov. 2013 - 28 Nov. 2013 - 平成２４年度小学校理科教育推進事業「理科授業の質の向上」推進地域モデル小学校公開授業研究会＠那珂市立横堀小学校
lecturer
15 Nov. 2012 - 15 Nov. 2012 - 平成２３年度「いばらきサイエンスキッズ育成プラン」推進地域モデル小学校授業研究会＠鹿嶋市立三笠小学校
lecturer
29 Nov. 2011 - 29 Nov. 2011 - 平成２２年度教員免許更新講習・新展開講習（理科・農業）「素粒子物理学入門」
lecturer
24 Aug. 2010 - 24 Aug. 2010 - 平成１９年度サイエンス・パートナーシップ・プログラム(SPP)事業「教員研修」・中学校理科「理数系教員指導力向上研修(希望型)」「素粒子の話」
lecturer
13 Oct. 2007 - 13 Oct. 2007 - 平成１８年度茨城大学公開講座「素粒子物理学入門 -基本的な考え方から超弦理論まで-」
lecturer
茨城大学生涯学習教育研究センター, Jun. 2006 - Jun. 2006 - 平成１７年度SPP事業による教員研修「橋で考える力の性質」
lecturer
22 Oct. 2005 - 22 Oct. 2005
