Dirac Kondo effect under magnetic catalysis

Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

Physical Review B, 108(24), p.245110_1 - 245110_11, 2023/12

https://doi.org/10.1103/PhysRevB.108.245110

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.

Phase diagram of the QCD Kondo effect and inactivation of the magnetic catalysis

Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

EPJ Web of Conferences, 276, p.01015_1 - 01015_5, 2023/03

https://doi.org/10.1051/epjconf/202327601015

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.

Heavy-quark spin polarization induced by the Kondo effect in a magnetic field

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

Physical Review D, 105(7), p.074028_1 - 074028_19, 2022/04

https://doi.org/10.1103/PhysRevD.105.074028

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.

Novel pentaquark picture for singly heavy baryons from chiral symmetry

Suenaga, Daiki*; Hosaka, Atsushi

Physical Review D, 104(3), p.034009_1 - 034009_7, 2021/08

https://doi.org/10.1103/PhysRevD.104.034009

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

https://doi.org/10.1103/PhysRevResearch.3.023098

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.

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

https://doi.org/10.1103/PhysRevResearch.3.013233

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.

QCD Kondo excitons

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

Physical Review Research (Internet), 2(2), p.023066_1 - 023066_11, 2020/04

https://doi.org/10.1103/PhysRevResearch.2.023066

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.

Casimir effect and spontaneous chiral symmetry braking in D mesons

Suzuki, Kei; Ishikawa, Tsutomu*; Nakayama, Katsumasa*; Suenaga, Daiki*

no journal, , 

D mesons are expected to be clear probes of the chiral condensate. For the Casimir effect in the QCD vacuum, non-perturbative properties of the QCD vacuum are modified by the volume size and boundary conditions. In this talk, we focus on the modification of the chiral symmetry breaking by the Casimir effect and the response of D mesons. By using an effective Lagrangian based on chiral partner structures for D mesons, we discuss the dependences on volume, boundary, and temperature, and the applications to lattice QCD simulations.

Can the QCD Kondo effect in a strong magnetic field co-prosper with the chiral condensate?

Hattori, Koichi*; Suenaga, Daiki*; Suzuki, Kei; Yasui, Shigehiro*

no journal, , 

no abstracts in English

Pressure and phase structure in pure Yang-Mills theory on the anisotropic boundary condition

Fujii, Daisuke; Iwanaka, Akihiro*; Suenaga, Daiki*; Kitazawa, Masakiyo*

no journal, , 

The Matsubara formalism for the thermal quantum field theory introduces temperature into the theory as a boundary condition along the imaginary time direction of Euclidean spacetime. In this study, we further consider the pure Yang-Mills theory on with boundary conditions in one spatial direction, and discuss thermodynamic quantities and their phase structures. The introducing of the boundary condition leads to the breaking of rotational symmetry, which results in anisotropy of the pressure. Results from lattice QCD simulations show that the anisotropic effect is suppressed until the spatial spread becomes significantly smaller near the critical temperature. This result is a very different behavior from that of free-particle systems. In order to reveal the mechanism behind this result, we employ an effective model with two Polyakov loops along the time and spatial directions. We show that introducing the competition between the two Polyakov loops as suggested in a previous study describes well the lattice data in the high temperature region. Furthermore, we show that a new first-order phase transition is suggested, which is different from the confinement phase transition.