Abstracts

Invited Talks

• Yasuhide Fukumoto (Kyushu University): "Dynamics of vortices, topological invariants and underlying symmetries for ideal fluid dynamics and magnetohydrodynamics"
  In 1858, von Helmholtz put forward the concept 'vorticity' of fluid flows and proved that vortex lines in an ideal fluid are frozen into the fluid. Helmloltz's law immediately implies that knots and links of vortex lines are preserved during their evolution. An associated integral invariant for ideal Euler flows in three dimensions is the helicity discovered in 1960s. This is no longer an invariant if density stratification and, for a conducting fluid, the Lorentz force are called into play. By appealing to Noether's theorem, we show that the cross-helicity is the integral invariant associated with the particle-relabeling symmetry of the action for ideal magnetohydrodynamics. Employing the Lagrange label function, as the independent variable in the variational framework, facilitates implementation of the relabeling transformation. The Casimirs in the form of integrals including Lagrangian invariants like the Ertel invariant are found to be variants of the cross-helicity. By incorporating the divergence symmetry, other known topological invariants are put on the same ground of Noether's theorem.
• Koichi Hattori (Zhejiang University): "Anisotropic linear waves in spin magnetohydrodynamics"
  We discuss formulation and solutions for relativistic spin hydrodynamics, motivated by recent experimental observations of spin polarized hadrons from the quark-gluon plasma. We extend spin hydrodynamics [1] toward "spin magneto-hydrodynamics (MHD)" that describes an intertwined time evolution of spinful fluid and a dynamical magnetic field [2]. We find a complete set of solutions near an equilibrium configuration with fully anisotropic transport coefficients [3].
  [1] Koichi Hattori, Masaru Hongo, Xu-Guang Huang, Mamoru Matsuo, Hidetoshi Taya, "Fate of spin polarization in a relativistic fluid: An entropy-current analysis," 1901.06615 [hep-th]
  [2] Zhe Fang, Koichi Hattori, Jin Hu, "Anisotropic linear waves and breakdown of the momentum expansion in spin magnetohydrodynamics," 2409.07096 [hep-ph]
  [3] Zhe Fang, Koichi Hattori, Jin Hu, "Analytic solutions for the linearized first-order magnetohydrodynamics and implications for causality and stability," 2402.18601
  
• Xu-Guang Huang (Fudan University): "Spin polarization and alignment in heavy ion collisions"
  Heavy-ion collisions offer a unique laboratory for probing the properties of the deconfined quark-gluon plasma (QGP). Among the most intriguing phenomena observed in these collisions are the spin polarization of hyperons and the spin alignment of vector mesons, which provide critical insights into the vortical structure, local angular momentum, and spin dynamics of the QGP. This talk will explore the current understanding of these phenomena, with a particular focus on the global and local polarization of hyperons, such as Lambda hyperons, as well as the spin alignment of phi mesons. Additionally, we will discuss the hydrodynamic and kinetic frameworks that have been developed to describe the dynamic evolution of spin polarization within the QGP.
• Yusuke Kato (University of Tokyo): "Quantum soliton in chiral magnetic chain"
  Chiral magnets are magnetic materials realized in the crystals with the spatial inversion symmetry and have non-trivial spin structures due to the Dzyaloshinsky-Moriya interaction[1,2]. Among those materials, we will focus on magnets with the Dzyalonshinskii-Moriya interaction with strong monoaxial anisotropy, which we call the monoaxial chiral magnets[2]. In those magnets, the ground state in the absence of magnetic fields exhibits the helical spin structure, which is referred to as the chiral soliton lattice. With applying the magnetic fields perpendicular to the helical axis, the spin structure starts to unwind and eventually becomes a uniformly polarized state at a certain magnetic field. This state evolution in the magnetization process has been worked out by Dzyaloshinskii in 1965 [3] and has been observed experimentally by Togawa et al. in 2012 [4]. The monoaxial chiral magnets have been discussed as the classical spin systems. Recently, we found that quantum spin chains of monoaxial chiral ferromagnet exhibit different magnetization processes for half-integer spin and integer spin, which is often referred to as the “spin parity effect”. i.e., different behaviors between even 2S and odd 2S. In this talk, we discuss the underlying physics of this spin parity effect. This work has been done in collaboration with S. Kodama and A. Tanaka. My talk is partly related to Kunimi’s talk (Jan. 20) on [6].
  [1] N. Nagaosa and Y. Tokura, Nature nanotechnology 8, 899 (2013).
  [2] Y. Togawa et al., J. Phys. Soc. Jpn. 85, 112001 (2016)
  [3] I. Dzyaloshinskii, Sov. Phys. JETP 20, 665 (1965).
  [4] Y. Togawa, et al., Phys. Rev. Lett. 108, 107202 (2012).
  [5] S. Kodama, A. Tanaka, and Y. Kato, Phys. Rev. B 107, 024403 (2023)
  [6] M. Kunimi, T. Tomita, H. Katsura, Y. Kato, Phys. Rev. A 110, 043312 (2024)
• Masaya Kunimi (University Tokyo of Science): "Proposal for simulating quantum spin models with Dzyaloshinskii-Moriya interaction using Rydberg atoms and construction of asymptotic quantum many-body scar states"
  Recent progress in quantum technology has made quantum simulations possible for various platforms. In particular, the Rydberg atom quantum simulators have attracted much attention. In these simulators, highly controllable quantum spin models can be realized experimentally owing to their strong interaction and optical tweezers technique [1]. In the talk, I will present a proposal for simulating quantum spin models with Dzyaloshinskii-Moriya (DM) interactions using Rydberg atoms in one-dimensional [2] and two-dimensional systems [3]. As a specific example, we demonstrate that a quantum spin model called the DH model [4], which consists of the DM interaction and the Zeeman energy term, can be realized within our proposal.
  I will also show our results on quantum many-body scar states (QMBS) in the DH model, which are special eigenstates of the nonintegrable Hamiltonian and violate the eigenstate thermalization hypothesis [5]. We prove the existence of QMBS states in the DH model [2]. In addition, we show that the recently proposed asymptotic QMBS (AQMBS) states [6] also exist in the DH model [2]. The AQMBS states have the property that the energy variance goes to zero in the thermodynamic limit. From this property, thermalization does not happen in the thermodynamic limit when the initial state is the AQMBS state. In this talk, I will present the analytical construction of the AQMBS states of the DH model and numerical results based on the matrix product states method.
  [1] A. Browaeys and T. Lahaye, Nature Phys. 16, 132 (2020).
  [2] MK, T. Tomita, H. Katsura, and Y. Kato, Phys. Rev A 110, 043312 (2024).
  [3] H. Kuji, MK, and T. Nikuni, arXiv:2408.04160 (2024).
  [4] S. Kodama et al., Phys. Rev. B 107, 024403 (2023).
  [5] C. J. Turner et al., Phys. Rev. B 98, 155134 (2018).
  [6] L. Gotta et al., Phys. Rev. Lett. 131, 190401 (2023).
  
• Kazuya Mameda (University Tokyo of Science): "Rotating Field Theory: Beyond Landau-Lifshitz-Pitaevskii"
  The observations of strong vorticity in quark-gluon plasma have sparked interest in rotational effects on relativistic quantum field theories. This talk shows recent theoretical developments in the thermodynamics of these systems, extending beyond the Landau-Lifshitz-Pitaevskii framework. I discuss crucial refinements needed for relativistic quantum field theories, focusing on relativistic causality, vacuum properties, and gauge invariance. The principle of gauge invariance reveals an intriguing interplay between rotation and external magnetic fields, potentially providing novel insights into angular momentum under magnetic fields. This opens up new avenues for research in orbitronics and related phenomena of Dirac electrons.
• Dung Xuan Nguyen (IBS, Korea): "Dual theories of the vortex lattice"
  Despite a long history of studies of vortex crystals in rotating superfluids, their melting due to quantum fluctuations is poorly understood. Here we develop a fracton-elasticity duality to investigate a two-dimensional vortex lattice within the fast rotation regime, where the Lifshitz model of the collective Tkachenko mode serves as the leading-order low-energy effective theory. We incorporate topological defects and discuss several quantum melting scenarios triggered by their proliferation. Furthermore, we lay the groundwork for a dual non-linear gravity description of the superfluid vortex crystals.
• Naoto Nagaosa (RIKEN): "Theory of Hopfions in magnets"
  Topological spin textures in magnets attract intense recent attentions in condensed matter physics including skyrmions, merons, monopoles, vortices and hopfions[1]. In this talk, I will focus on the hopfion, three-dimensional spin texture characterized by the Hopf number, and its stability [2] and current driven dynamics [3],[4]. The collaborators of this work are Drs. Yizhou Liu and Hikaru Watanabe.
  [1] N. Nagaosa and Y. Tokura, Nat.Nanotechnol.8, 899(2013).
  [2] Y. Liu, W. Hou, X. Han, and J. Zang, Phys. Rev. Lett. 124, 127204 (2020).
  [3] Y. Liu, H. Watanabe, and N. Nagaosa, Phys. Rev. Lett. 129, 267201 (2022). [4] Y. Liu, and N. Nagaosa, Phys. Rev. Lett. 132, 126701 (2024).
  
• Takashi Sakajo (Kyoto University): "Vortex and Topology: Recent Topics in Topological Fluid Mechanics"
  In the study of fluid dynamics, while we usually consider the motion of fluids in Euclidean space, we are interested in how the behavior of fluids is affected by the flow domains having various geometric features, such as when the domain contains multiple islands or when it is curved such as a sphere or a curved torus. This problem is not only of mathematical interest, but it is also an important one from the application points of view when describing atmospheric and ocean flows and flows in industrial devices with complex shapes. The research field dealing with such problems is known as topological fluid dynamics.
  In this talk, I would like to provide an overview of the following two recent topics focusing on "vortex and topology" that our research group is investigating and discuss the possibility of future collaborations with the participants. The first topic introduces the results of the dynamics of point vortices on two-dimensional flow domains with multiple boundaries and closed surfaces such as a sphere and a torus. Here, we investigate how the topological and geometric features of flow domains affect the vortex motion. The second topic is a new method of topological data analysis named Topological Flow Data Analysis (TFDA). The topological structure of a given flow pattern is uniquely converted into a plane graph, named partially Cyclically Ordered rooted labeled Tree (COT), and its associated string expression (COT representation). Each character in the COT representation describes a local flow structure in the flow pattern, and its global configuration is represented by a graph or a sequence of letters in a line. Furthermore, TFDA reduces the continuous long-time evolution of flow patterns to a discrete dynamical system between topologically equivalent flow patterns, which allows us to track the evolution of some quantities associated with topological structures of orbits. I will present the recent developments of TFDA with its applications to various problems in atmospheric science, and clinical medicine.
• Makoto Tsubota (Osaka Metropolitan University): "Quantized vortices in rotating superfluid"
  Quantized vortices are topological defects appearing in Bose-Einstein condensates(BECs), being studied extensively in low temperature quantum condensates like superfluid helium and atomic BECs. We discuss some interesting topics on quantized vortices.
  1. Quantized vortex compared with usual vortices
  2. Vortex lattice formation in rotating BECs
  3. Vortex lattice in two-component BECs
  4. Quantum turbulence

Contributed talks

• Nicholas J. Benoit (Hiroshima University): "A discussion on the effects of QGP's electric conductivity on observables in high-energy heavy-ion collisions"
  Heavy-ion collisions have been used to study quark-gluon plasma (QGP) and can be used to study strong electromagnetic (EM) fields. Because the EM fields penetrate the QGP medium, their evolutions are coupled together. In turn, probes like the flow of direct photons and charged particles will be modified by the coupling [1, 2]. We model the evolution of the QGP and EM fields using relativistic resistive magneto-hydrodynamics (RRMHD) [3]. Our RRMHD model is unique for heavy-ion collisions because it includes a finite scalar electrical conductivity. We demonstrate how the charged particle directed flow (v1) depends on QGP conductivity. Additionally, we apply the same model to calculate a potentially cleaner observable, the direct photon elliptic flow (v2). Because system should have the same conductivity for both calculations, we will compare and discuss the preferred values of both.
  [1] Sun and Yan, Phys. Rev.C 109, 034917 (2024).
  [2] Gursoy, Kharzeev, and Rajagopal, Phys. Rev.C 89, 054905 (2014),
  [3] Nakamura, Miyoshi, Nonaka, and Takahashi, Phys.Rev.C 107, 014901 (2023).
  Nakamura, Miyoshi, Nonaka, and Takahashi, Eur.Phys. J.C 83, 229 (2023).
  Nakamura, Miyoshi, Nonaka, and Takahashi, Phys.Rev.C 107, 034912 (2023).
  
• Shuai Wang (Fudan University): "Chiral magnetovortical instability in a rotating frame"
  We have demonstrated that in a chiral plasma subject to an external magnetic field, the chiral vortical effect can induce a new type of magnetohydrodynamic instability: the chiral magnetovortical instability (CMVI) [1]. This instability arises from the mutual evolution of the magnetic and vortical fields and satisfies 𝜉𝜔 > √𝜌, the chiral vortical coefficient is larger than the mass density. It can cause a rapid amplification of the magnetic fields by transferring the chirality of the constituent particles to the cross helicity of the plasma.
  By considering rigid rotation, we find more excited wave modes, which can be interpreted as the complex interplay between inertial waves, Alfvén waves and anomalous effects [2]. Notably, the criterion for CMVI is modified by the presence of rotation, especially the chiral vortical coefficient can be taken to a smaller value, for example 𝜉𝜔 < √𝜌 . This alteration is primarily driven by the influence of inertial waves and an additional chiral vortical current. The rotation plays a critical role to trigger this new instability, we will briefly discuss the possible relevance in heavy ion collisions and other extreme conditions.
  [1] S. Wang and X.-G. Huang, Chiral magnetovortical instability, Phys. Rev. D 109, L121302 (2024).
  [2] In preparing.
• Takuma Kamakubo (University of Tokyo): "Dynamics of Domain Walls and Quantum Vortices in type-II Superconductors Under Gradients of Temperature/Spin Density"
  Quantum vortices in type-II superconductors are known to have significant impacts on the transport properties of superconductors, thus improving the controllability of the motion of vortices has been a crucial issue. The most common method to drive vortices is the use of transport currents. In [1][2], we defined the driving force on a vortex as the sum of the magnetic and hydrodynamic forces in the framework of the time-dependent Ginzburg-Landau (TDGL) theory. We expected that the results could be extended to establish a similar picture for other driving methods, such as heat flows [3][4] and inhomogeneous spin polarization [5-8]. In [9], we investigated the dynamics of domain walls, one-dimensional topological defects, under the influence of the temperature gradient or the inhomogeneous spin polarization. The system of equations consists of the TDGL equation and the thermal / spin diffusion equation. We have shown, both analytically and numerically, that the domain walls move to the higher temperature region, where the order parameter is suppressed. This result is understood as a process reducing the loss of in the condensation energy (cf. pinning of vortices). In this presentation, we also discuss the dynamics of quantum vortices under a temperature gradient. We incorporated Ampere's law, which we did not consider in case of the dynamics of domain walls, into the system of equations.
  References
  [1] Y. Kato and C-K Chung, J. Phys. Soc. Jpn. 85, 033703/1-5 (2016).
  [2] S. Sugai, N. Kurosawa and Y. Kato, Phys. Rev. B 104, 064516 (2021).
  [3] M. J. Stephen, Phys. Rev. Lett, 16, 801 (1966).
  [4] I. S. Veshchunov et al., Nat. Commun. 7, 12801 (2016).
  [5] Se Kwon Kim et al., Phys. Rev. Lett. 121, 187203 (2018).
  [6] A. Vargunin and M. Silaev, Sci. Rep. 9, 5914 (2019).
  [7] T. Taira et al., Phys. Rev. B 103, 134417 (2021).
  [8] H. Adachi, Y. Kato, J.-i. Ohe, and M. Ichioka, Phys. Rev. B 109, 174503 (2024).
  [9] T. Kanakubo et al., Interplay between Domain Walls in Type-II Superconductors and Gradients of Temperature/Spin Density, arXiv:2405.10200 (2024).
• Masakiyo Kitazawa (YITP, Kyoto University): "First-order phase transition and critical points on SU(3) Yang-Mills theory on T^2xR^2"
  We investigate thermodynamics and phase structure of SU(3) Yang-Mills theory on T^2xR^2 with anisotropic spatial volumes in Euclidean spacetime in lattice numerical simulations and an effective model. In lattice simulations, it is found that a clear pressure anisotropy is observed only at a significantly shorter spatial extent compared with the free scalar theory. We then study the thermodynamics obtained on the lattice in an effective model that incorporates two Polyakov loops along two compactified directions as dynamical variables. The model is constructed to reproduce thermodynamics measured on the lattice. The model analysis indicates the existence of a novel first-order phase transition and critical points as its endpoints. We argue that the interplay of the Polyakov loops induces the first-order transition.
• Zhibin Zhu (Fudan University): "Chiral phase transition under acceleration and rotation"
  In the relativistic heavy ion collision experiment, there exists a large acceleration and rapid rotation in the non-central collision which can be considered as a system with acceleration and rotation. As the QGP is the most vortical fluid, QCD matter under rotation has attracted much attention in recent years while the effects from acceleration are much less discussed. According to the Hawking-Unruh effect, the accelerated observer sees himself in a system with Unruh temperature $T=a/2\pi$. And the color glass condensate picture predicts that in heavy ion collision, the particle under a strong color-electric field with strength $E\sim Q^2_s/g$ ($Q_S$ is the saturation scale, and g is the strong coupling) will provide a typical acceleration $a \sim Q_s \sim 1 GeV$ such that the Unruh temperature $T\sim 200 MeV$ which means the Unruh effect may play an important role in QCD phase transition.
  Using field theory in general spacetime, we study the chiral phase transition observed by an accelerating and rotating observer. Using the Nambu-Jona-Lasinio model in an accelerating and rotating frame, we develop the formalism to calculate the chiral condensate. We solve the gap equation and obtain the chiral condensate as a function of proper acceleration and angular velocity. We also defined a critical acceleration $a_c$ where the chiral symmetry is restored. As one of our main results, $a_c$ as a function of rotation angular velocity $\omega$ was obtained. We are also interested in a phase diagram in the axes of acceleration and temperature, as measured by a comoving observer and some results are obtained.