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Journal Articles

Spin-orbital magnetic response of relativistic fermions with band hybridization

Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review Research (Internet), 3(2), p.023098_1 - 023098_17, 2021/05

Spins of relativistic fermions are related to their orbital degrees of freedom. In order to quantify the effect of hybridization between relativistic and nonrelativistic degrees of freedom on spin-orbit coupling, we focus on the spin-orbital (SO) crossed susceptibility arising from spin-orbit coupling. The SO crossed susceptibility is defined as the response function of their spin polarization to the "orbital" magnetic field, namely the effect of magnetic field on the orbital motion of particles as the vector potential. Once relativistic and nonrelativistic fermions are hybridized, their SO crossed susceptibility gets modified at the Fermi energy around the band hybridization point, leading to spin polarization of nonrelativistic fermions as well. These effects are enhanced under a dynamical magnetic field that violates thermal equilibrium, arising from the interband process permitted by the band hybridization. Its experimental realization is discussed for Dirac electrons in solids with slight breaking of crystalline symmetry or doping, and also for quark matter including dilute heavy quarks strongly hybridized with light quarks, arising in a relativistic heavy-ion collision process.

Journal Articles

Chiral separation effect catalyzed by heavy impurities

Suenaga, Daiki*; Araki, Yasufumi; Suzuki, Kei; Yasui, Shigehiro*

Physical Review D, 103(5), p.054041_1 - 054041_17, 2021/03

 Times Cited Count:1 Percentile:63.46(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.

Journal Articles

Two relativistic Kondo effects; Classification with particle and antiparticle impurities

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.

Journal Articles

Kondo effect driven by chirality imbalance

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.

Journal Articles

QCD Kondo excitons

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.

Journal Articles

Flavor-singlet hidden charm pentaquark

Irie, Yoya*; Oka, Makoto; Yasui, Shigehiro*

Physical Review D, 97(3), p.034006_1 - 034006_12, 2018/02

 Times Cited Count:11 Percentile:66.25(Astronomy & Astrophysics)

One type of hidden charm pentaquark $$P_{cs}$$ with quark content $$cbar c uds$$ in light-flavor singlet state is studied in the quark model. This state is analogous to the $$P_c$$ with $$cbar c uud$$ in light-flavor octet, which was observed in LHC in 2015. Considering various combinations of color, spin, and light flavor as internal quantum numbers in $$P_{cs}$$, we investigate the mass ordering of the $$P_{cs}$$'s by adopting both the one-gluon exchange interaction and the instanton-induced interaction in the quark model. The most stable configuration of $$P_{cs}$$ is identified to be total spin 1/2 in which the $$cbar c$$ is combined to be color octet and spin 1, while the uds cluster is in a color octet state. The other color octet configurations, the total spin $$1/2$$ state with the $$cbar c$$ spin 0, and the state with total spin $$3/2$$ and $$cbar c$$ spin 1, are found as excited states. We also discuss possible decay modes of these hidden charm pentaquarks.

Journal Articles

Exotic hadrons from heavy ion collisions

Cho, S.*; Hyodo, Tetsuo*; Jido, Daisuke*; Ko, C. M.*; Lee, S. H.*; Maeda, Saori*; Miyahara, Kenta*; Morita, Kenji*; Nielsen, M.*; Onishi, Akira*; et al.

Progress in Particle and Nuclear Physics, 95, p.279 - 322, 2017/07

AA2016-0538.pdf:0.65MB

 Times Cited Count:54 Percentile:86.05(Physics, Nuclear)

With upgraded detectors at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), it has become possible to measure hadrons beyond their ground states in high energy heavy ion collisions. Therefore, heavy ion collisions provide a new method for studying exotic hadrons that are either molecular states made of various hadrons or compact system consisting of muliquarks. Because their structures are related to the fundamental properties of Quantum Chromodynamics (QCD), studying exotic hadrons is currently one of the most active areas of research in hadron physics. The present review is a summary of the current understanding of a selected set of exotic candidate particles that can be potentially measured in heavy ion collisions.

Journal Articles

Two-body wave functions, compositeness, and the internal structure of dynamically generated resonances

Sekihara, Takayasu; Hyodo, Tetsuo*; Jido, Daisuke*; Yamagata-Sekihara, Junko*; Yasui, Shigehiro*

Proceedings of Science (Internet), 8 Pages, 2017/05

Journal Articles

Structure of charmed baryons studied by pionic decays

Nagahiro, Hideko*; Yasui, Shigehiro*; Hosaka, Atsushi; Oka, Makoto; Noumi, Hiroyuki*; Noumi, Hiroyuki*

Physical Review D, 95(1), p.014023_1 - 014023_20, 2017/01

 Times Cited Count:39 Percentile:92.61(Astronomy & Astrophysics)

We investigate the decays of the charmed baryons aiming at the systematic understanding of hadron internal structures based on the quark model by paying attention to heavy quark symmetry. We evaluate the decay widths from the one pion emission for the known excited states, $$Lambda^*_c(2595)$$, $$Lambda^*_c(2625)$$, $$Lambda^*_c(2765)$$, $$Lambda^*_c (2880)$$ and $$Lambda^*_c(2940)$$, as well as for the ground states $$Sigma_c(2455)$$ and $$Sigma^*_c(2520)$$. The calculated decay widths are in good agreement with the experimental data, and several important predictions for higher excited $$Lambda^*_c$$ baryons are given. We also find that the axial-vector type coupling of the pion to the light quarks is essential, which is expected from chiral symmetry, to reproduce the decay widths especially of the low lying $$Lambda^*_c$$ baryons. We emphasize the importance of the branching ratios of $$Gamma(Sigma^*_c pi)/Gamma(Sigma_c pi)$$ for the study of the nature of higher excited $$Lambda^*_c$$ baryons.

Oral presentation

Spin-orbital crossed magnetic response under band hybridization

Araki, Yasufumi; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

no journal, , 

no abstracts in English

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