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Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review B, 108(24), p.245110_1 - 245110_11, 2023/12
Times Cited Count：0 Percentile：0(Materials Science, Multidisciplinary)We develop a mean-field theory of a novel Kondo effect emerging in systems without a Fermi surface, which instead emerges under strong magnetic fields. We determine the magnitude of the Kondo condensate, which is a particle pairing composed of conducting Dirac fermions and localized impurities. We focus on the competition between the Kondo effect and the energy gap formation that stems from the pairing among the Dirac fermions leading to the dynamical chiral symmetry breaking. We find that this competition induces a quantum critical point. We also investigate finite-temperature effects. This system at vanishing fermion density can be studied with Monte Carlo lattice simulations, which do not suffer from the sign problem.
Kim, Y.*; Oka, Makoto; Suenaga, Daiki*; Suzuki, Kei
Physical Review D, 107(7), p.074015_1 - 074015_15, 2023/04
Times Cited Count：1 Percentile：54.75(Astronomy & Astrophysics)A chiral effective theory of scalar and vector diquarks is formulated, which is based on 
chiral symmetry and includes interactions between scalar and vector diquarks with one or two mesons. We find that the diquark interaction term with two mesons breaks the 
and flavor 
symmetries. To determine the coupling constants of the interaction Lagrangians, we investigate one-pion emission decays of singly heavy baryons 
(
, 
and 
, 
, 
), where baryons are regarded as diquark-heavy-quark two-body systems. Using this model, we present predictions of the unobserved decay widths of singly heavy baryons. We also study the change of masses and strong decay widths of singly heavy baryons under partial restoration of chiral symmetry.
Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
EPJ Web of Conferences, 276, p.01015_1 - 01015_5, 2023/03
Times Cited Count：0 Percentile：0.91(Physics, Atomic, Molecular & Chemical)We investigate the QCD phase diagram in strong magnetic fields with heavy-quark impurities and determine the ground state within the mean-field analysis. The ground state is characterized by magnitudes of the pairing not only between the light quark and antiquark, i.e., chiral condensate, but also between the light quark and heavy-quark impurity, dubbed the Kondo condensate. We propose signatures of the interplay and/or competition between those two pairing phenomena reflected in the magnitude of the chiral condensate that is saturated with respect to the magnetic-field strength and anomalously increases with increasing temperature.
Suenaga, Daiki*; Araki, Yasufumi; Suzuki, Kei; Yasui, Shigehiro*
Physical Review D, 105(7), p.074028_1 - 074028_19, 2022/04
Times Cited Count：2 Percentile：36.77(Astronomy & Astrophysics)We propose a new mechanism of the heavy-quark spin polarization (HQSP) in quark matter induced by the Kondo effect under an external magnetic field. The Kondo effect is caused by a condensate between a heavy and a light quark called the Kondo condensate leading to a mixing of the heavy- and light-quark spins. Thus, the HQSP is driven through the Kondo effect from light quarks coupling with the magnetic field in quark matter. For demonstration, we employ the Nambu-Jona-Lasinio type model under a magnetic field and investigate the HQSP within the linear response theory with vertex corrections required by the 
electromagnetic gauge invariance. As a result, we find that the HQSP arises significantly with the appearance of the Kondo effect. Our findings are testable in future sign-problem-free lattice simulations.
Kim, Y.*; Oka, Makoto; Suzuki, Kei
Physical Review D, 105(7), p.074021_1 - 074021_17, 2022/04
Times Cited Count：15 Percentile：93.15(Astronomy & Astrophysics)Energy spectrum of doubly heavy tetraquarks, 
(
with 
and 
), is studied in the potential chiral-diquark model. Using the chiral effective theory of diquarks and the quark-diquark-based potential model, the 
, 
, and 
tetraquarks are described as a three-body system composed of two heavy quarks and an antidiquark. We find several bound states, while no and (deep) bound state is seen. We also study the change of the tetraquark masses under restoration of chiral symmetry.
Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suzuki, Kei
Physical Review D, 104(9), p.094515_1 - 094515_11, 2021/11
Times Cited Count：4 Percentile：37.94(Astronomy & Astrophysics)We investigate the Kondo effect with Wilson fermions. This is based on a mean-field approach for the chiral Gross-Neveu model including four-point interactions between a light Wilson fermion and a heavy fermion. For massless Wilson fermions, we demonstrate the appearance of the Kondo effect. We point out that there is a coexistence phase with both the light-fermion scalar condensate and Kondo condensate, and the critical chemical potentials of the scalar condensate are shifted by the Kondo effect. For negative-mass Wilson fermions, we find that the Kondo effect is favored near the parameter region realizing the Aoki phase. Our findings will be useful for understanding the roles of heavy impurities in Dirac semimetals, topological insulators, and lattice simulations.
Kim, Y.*; Liu, Y.-R.*; Oka, Makoto; Suzuki, Kei
Physical Review D, 104(5), p.054012_1 - 054012_18, 2021/09
Times Cited Count：12 Percentile：74.69(Astronomy & Astrophysics)Chiral effective theory of scalar and vector diquarks is formulated according to the linear sigma model. The main application is to describe the ground and excited states of singly heavy baryons with a charm or bottom quark. Applying the potential quark model between the diquark and the heavy quark (
), we construct a heavy-quark-diquark model. The spectra of the positive- and negative-parity states of 
, 
, 
and 
are obtained. The masses and interaction parameters of the effective theory are fixed partly from the lattice QCD data and also from fitting low-lying heavy baryon masses. We find that the negative parity excited states of 
(flavor 
) are different from those of , because of the inverse hierarchy of the pseudoscalar diquark. On the other hand, 
and (flavor 
) baryons have similar spectra. We compare our results of the heavy-quark-diquark model with experimental data as well as the quark model.
Iwasaki, Sachio*; Oka, Makoto; Suzuki, Kei
European Physical Journal A, 57(7), p.222_1 - 222_14, 2021/07
Times Cited Count：17 Percentile：70.63(Physics, Nuclear)We review the properties of quarkonia under strong magnetic fields. The main phenomena are (i) mixing between different spin eigenstates, (ii) quark Landau levels and deformation of wave function, (iii) modification of 
potential, and (iv) the motional Stark effect. For theoretical approaches, we review (i) constituent quark models, (ii) effective Lagrangians, (iii) QCD sum rules, and (iv) holographic approaches.
Suenaga, Daiki*; Araki, Yasufumi; Suzuki, Kei; Yasui, Shigehiro*
Physical Review D, 103(5), p.054041_1 - 054041_17, 2021/03
Times Cited Count：5 Percentile：45.23(Astronomy & Astrophysics)We investigate the influence of the Kondo effect, namely, the nonperturbative effect induced by heavy impurities, on the chiral separation effect (CSE) in quark matter. We employ a simple effective model incorporating the Kondo condensate made of a light quark and a heavy quark, and compute the response function of the axial current to the magnetic field in the static and dynamical limits. As a result, we find that the Kondo effect catalyzes the CSE in both of the limits, and in particular the CSE in the dynamical limit can be enhanced by a factor of approximately 3. Our findings clearly show that the presence of heavy impurities in quark matter can play an important role in the transport phenomena of light quarks induced by a magnetic field.
Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 3(1), p.013233_1 - 013233_12, 2021/03
We investigate two different types of relativistic Kondo effects, distinguished by heavy-impurity degrees of freedom, by focusing on the energy-momentum dispersion relations of the ground state with condensates composed of a light Dirac fermion and a nonrelativistic impurity fermion. Heavy fermion degrees of freedom are introduced in terms of two types of heavy-fermion effective theories, in other words, two heavy-fermion limits for the heavy Dirac fermion, which is known as the heavy-quark effective theories (HQETs) in high-energy physics. While the first one includes only the heavy-particle component, the second one contains both the heavy-particle and heavy-antiparticle components, which are opposite in their parity. From these theories, we obtain two types of Kondo effects, in which the dispersions near the Fermi surface are very similar, but they differ in the structure at low momentum. We also classify the possible forms of condensates in the two limits. The two Kondo effects will be examined by experiments with Dirac/Weyl semimetals or quark matter, lattice simulations, and cold-atom simulations.
Rohrhofer, C.*; Aoki, Yasumichi*; Cossu, G.*; Fukaya, Hidenori*; Gattringer, C.*; Glozman, L. Ya.*; Hashimoto, Shoji*; Lang, C. B.*; Suzuki, Kei
Proceedings of Science (Internet), 363, p.227_1 - 227_7, 2020/08
Properties of QCD matter change significantly around the chiral crossover temperature, and the effects on and topological susceptibilities, as well as the meson spectrum have been studied with much care. Baryons and the effect of parity doubling in this temperature range have been analyzed previously by various other groups employing different setups. Here we construct suitable operators to investigate chiral and axial symmetries in the baryon spectrum. Measurements for different volumes and quark-masses are done with two flavors of chirally symmetric domain-wall fermions at temperatures above the critical one. The possibility of emergent 
and 
symmetries is discussed.
Suenaga, Daiki*; Suzuki, Kei; Araki, Yasufumi; Yasui, Shigehiro*
Physical Review Research (Internet), 2(2), p.023312_1 - 023312_13, 2020/06
The Kondo effect is induced by the interaction between light fermions near the Fermi surface and heavy impurities, and it affects electric/thermal/transport properties of matter. The chirality (right-handed or left-handed) is one of the unique properties of relativistic (Dirac or Weyl) fermions. In normal matter, the numbers of right- and left-handed particles are equivalent to each other, but environments with a chirality imbalance can also be realized. In this paper, we theoretically propose the Kondo effect driven by a chirality imbalance (or chiral chemical potential) of relativistic light fermions. This effect is caused by the mixing between a right-handed (or left-handed) fermion and a heavy impurity in the chirality imbalanced matter. This is different from the usual Kondo effect induced by finite density (or chemical potential) for light fermions. We construct an effective model with an interaction between a relativistic fermion and a heavy impurity, and we derive the realization of the Kondo effect from both a perturbative calculation and a nonperturbative mean-field approach. We also discuss the temperature dependence, the coupling constant dependence, the susceptibilities, and the order of the phase transition for the Kondo effect. Such a Kondo effect will be tested by future lattice simulations.
Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*
Physical Review Research (Internet), 2(2), p.023066_1 - 023066_11, 2020/04
The QCD Kondo effect is a quantum phenomenon in which heavy (charm or bottom) quarks exist as impurity particles in quark matter composed of light quarks at extremely high density. In this paper, we theoretically predict the existence of the exciton modes above the ground state of the quark matter governed by the QCD Kondo effect. We construct an effective model based on the mean field approximation and investigate possible quantum numbers (such as spin and parity) of excitons and their dispersion relations. These excitons can be electrically (color) neutral, so that they are observed as the neutral currents in transport phenomena. As a result, they contribute to violation of the Wiedemann-Franz law for the electric (color) and heat conductivities. Such Kondo excitons are an universal phenomenon for relativistic (Dirac or Weyl) fermions, and the same concept will also be applied to Dirac or Weyl electron systems.
mesons as a probe of Casimir effect for chiral symmetry breakingIshikawa, Tsutomu*; Nakayama, Katsumasa*; Suenaga, Daiki*; Suzuki, Kei
Physical Review D, 100(3), p.034016_1 - 034016_14, 2019/08
Times Cited Count：5 Percentile：31.16(Astronomy & Astrophysics)We propose mesons as probes to investigate finite-volume effects for chiral symmetry breaking at zero and finite temperatures. By using the 2+1-flavor linear sigma model with constituent light quarks, we analyze the Casimir effects for the 
mean fields; the chiral symmetry is rapidly restored by the antiperiodic boundary for light quarks, and the chiral symmetry breaking is catalyzed by the periodic boundary. We also show the phase diagram of the mean fields on the volume and temperature plane. For mesons, we employ an effective model based on the chiral-partner structure, in which the volume dependence of mesons is induced by the mean fields. We find that 
mesons are less sensitive to finite volume than mesons, which is caused by the insensitivity of 
mean fields. An anomalous mass shift of mesons at high temperature with the periodic boundary will be useful in examinations with lattice QCD simulations. The dependence on the number of compactified spatial dimensions is also studied.
Maruyama, Toshiki; Chiba, Satoshi
JAERI-Conf 2003-009, 233 Pages, 2003/08
JAERI-Conf-2003-009.pdf:15.94MB
The fifth symposium on Science of Hadrons under Extreme Conditions, organized by the Research Group for Hadron Science, Advanced Science Research Center, was held at Tokai Research Establishment of JAERI on March 18 to 20, 2003. The symposium was devoted for discussions and presentations of research results in wide variety of hadron physics such as nuclear matter, hypernuclei, neutron stars, supernovae, nucleosynthesis, heavy-ion reactions, quark matter and quantum chromodynamics to understand various aspects of hadrons under extreme conditions. Thirty three papers on these topics presented at the symposium aroused lively discussions among approximately 50 participants. The concluding remark for the "research group for hadron science" and the explanation of next project "research group for manybody theory of hadron systems" was also presented by the group leader Dr. S. Chiba with gratitude to the participants and to all the scientists concerned.
Chiba, Satoshi; Maruyama, Toshiki
JAERI-Conf 2002-011, 231 Pages, 2002/09
JAERI-Conf-2002-011.pdf:17.42MB
no abstracts in English
Fukushima, Masahiro; Suganuma, Hideo*; Chiba, Satoshi
Progress of Theoretical Physics, 107(6), p.1147 - 1161, 2002/06
Times Cited Count：1 Percentile：13.39(Physics, Multidisciplinary)Quantum Chromodynamics (QCD) is established as the standard theory of the strong interaction. Based on the lattice gauge theory, we investigate a deformation of stabilized instanton solutions in a nontrivial topological sector and further discuss appearance of monopole trajectories around the instanton.
Fukushima, Masahiro; Ilgenfriz, E. -M.*; Toki, Hiroshi*
Physical Review D, 64(3), p.034503_1 - 034503_9, 2001/08
Times Cited Count：7 Percentile：39.32(Astronomy & Astrophysics)no abstracts in English
Chiba, Satoshi
JAERI-Conf 2000-011, 148 Pages, 2000/08
JAERI-Conf-2000-011.pdf:9.22MB
no abstracts in English
Oka, Makoto
no journal, ,
Diquarks are important degrees of freedom for the structure and dynamics of hadrons, in particular multi-quark hadrons, which are recently observed in experiment. We propose a chiral effective theory for colored diquarks based on the chiral representations of scalar and pseudoscalar diquarks. The effective Lagrangian can possess two mass terms, a chiral invariant and a chiral symmetry breaking terms. From Lattice QCD calculations of diquark specrum, we can determine each term separately and thus can predict the behaviors of diquarks under the change of chiral condensates. We further introduce vector and axialvector diquarks in the effective theory.
