Abstracts

Invited Lectures

1. Mark G. Alford (Washington University in St. Louis): "Nuclear matter in mergers: the quest for equilibrium"
   In a neutron star merger, nuclear matter experiences dramatic changes in temperature and density that happen in milliseconds. Mergers therefore probe dynamical properties that may help us uncover the phase structure of ultra-dense matter. I will describe some of the relevant material properties, focusing on chemical (beta) equilibration and its consequences such as bulk viscosity and damping of oscillations.
2. Gordon Baym (University of Illinois Urbana-Champaign/RIKEN iTHEMS): "Matter under extreme conditions -- from neutron stars to nucleons"
   Two playgrounds for exploring condensed matter phenomena in QCD are neutron stars, which if massive enough may contain quark matter cores, and high energy electron-nucleon and electron-nucleus collisions. In this pair of talks I will first review the basic structure of neutron stars, discuss the transition to quark matter in their deep interiors, and evidence from NICER of the onset of quark degrees of freedom. I will discuss the tantalizing problems of vortices in quark matter, and briefly review the prospects at the forthcoming Electron-Ion Collider (the EIC) of studying collective behavior among the huge density of low energy gluons in the nucleon.
3. Muneto Nitta (Keio University): "Topological aspects of nuclear and quark matter"
   Lecture 1: “Topological Aspects of Nuclear Matter in Magnetic Field”
   I will summarize the current understanding of chiral soliton lattice (CSL) and domain-wall Skyrmion phase in QCD matter with finite baryon chemical potential and magnetic field. A chiral soliton lattice (CSL), an array of neutral pion solitons, perpendicular to the magnetic field is the ground state in a region of higher baryon chemical potential and/or stronger magnetic field. Recently, almost all the region of CSL is found to be covered by a “domain-wall Skyrmion phase,” in which topological lumps (baby Skyrmions) have negative mass and appear on top of the CSL. These lumps are superconducting rings on the solitons, and are Skyrmions in the bulk point of view.
   The situation becomes completely different by introducing the isospin chemical potential. In this case, charged pions are condensed in the uniform ground state. In the zero pion mass limit, there appears a new type of phase in the phase diagram spanned by the baryon and isospin chemical potentials, that is a “vortex-Skyrmion phase,” in which vortex-Skyrmions (baryonic vortices, or vortices carrying baryon numbers) have negative tension and appear.
   Lecture 2: “On vortices penetrating through quark-hadron continuity”
   I will comment on how vortices penetrate along nuclear and quark matter. In the three-flavor symmetric case, superfluid vortices and non-Abelian vortices (color flux tubes) are present in the dibaryon condensates and color-flavor locking phase, respectively. In the two-flavor case, superfluid vortices and non-Abelian Alice strings are present in 3P2 superfluid and (hypothetical) 2SC + dd phase, respectively. I discuss how they should connect.
4. Sanjay Reddy (University of Washington): "Thermal and transport properties of dense matter and their implications for astrophysics"
   Lecture 1: I will begin by summarizing what we currently know about the structure of neutron stars and review various theoretical proposals for the states of matter at high density and low temperature. This will be followed by a pedagogic introduction to low-energy excitations in the Fermi liquid, superfluid, superconducting, and crystalline states of dense nuclear and quark matter that are expected to play a key role in the thermal, spin, and magnetic evolution of neutron stars.
   Lecture 2: The neutrino scattering, absorption, and emission rates in dense neutron star matter determine transport properties such as thermal conductivity and shear viscosity. I will discuss the formalism needed to calculate these rates and provide a few examples to illustrate the important role of collective modes and correlations. I will conclude with a brief discussion of neutrino emission from supernovae and neutron star mergers and the thermal evolution of neutron stars on longer time scales.
5. Dam T. Son (The University of Chicago): "Effective theories of Fermi liquids and Relativistic guiding-center motion"
   Lecture 1: Fermi liquids and coadjoint orbits
   I will outline a new method that leads to a field-theoretical reformulation of Landau Fermi liquid theory. In this approach, low-energy states of a system with a Fermi surface is described as a coadjoint orbit of the group of canonical transformations acting on the single-particle phase space. The method naturally leads to a nonlinear bosonized theory of the Fermi surface. The Kirillov-Kostant-Souriau symplectic form on the coadjoint orbit gives rise to a Berry-phase term in the effective action. We show how the resulting local effective field theory can capture linear and nonlinear effects in Landau’s Fermi liquid theory.
   Lecture 2: Relativistic guiding-center motion: Action principle, kinetic theory, and hydrodynamics
   The problem of the motion of the guiding center of a charged particle in a slowly changing magnetic field is a classic problem of plasma physics. In the relativistic setting, this problem has been fully solved by Peter Vandervoort in 1960. However, the equation written down by Vandervoort is not manifestly Lorentz covariant. I will present a fully Lorentz covariant description of the guiding-center motion based on an action principle. From the Lorentz-covariant guiding-center equation of motion, we derive the kinetic theory and the ideal hydrodynamic theory describing a fluid of guiding centers in a background electromagnetic field. (Based on work in progress with Misha Stephanov)
6. Mikhail Stephanov (University of Illinois Chicago): "QCD critical point and hydrodynamic fluctuations in relativistic fluids"
   The talk will describe recent progress in the theory of fluctuations relevant for the QCD critical point search in heavy-ion collisions, in particular, the hydrodynamics of non-Gaussian fluctuations and the novel approach to their freezeout consistent with conservation laws based on maximum entropy principle.

Invited Talks

1. Kenji Fukushima (The University of Tokyo): "Pulsar Kick -- Anisotropy, Scattering, and Their Interplay"
   The pulsars move at unexplainably fast velocities. This pulsar-kick problem will be quickly reviewed. Several mechanisms have been proposed so far. Anisotropic explosion is the most conventional, but it cannot reproduce the observed kick. Parity violating weak scattering with magnetic fields is also a natural mechanism and chiral transport in the hydrodynamic regime is an intriguing scenario. We recently discussed a hybrid picture, i.e., weak scattering with a chiral transport background on top of anisotropy, and found that their interplay leads to a novel effect to accelerate the pulsars, which will be closely explained in this talk.
2. Naoki Yamamoto (Keio University): "Parity violation of the weak interaction and supernovae"
   Neutrinos play essential roles in the evolution of core-collapse supernovae. However, the conventional neutrino kinetic theory violates the basic tenet of low-energy effective theories in that it does not respect the symmetry (or parity violation) due to the chirality of neutrinos. In this talk, we discuss the formulation of the chiral radiation transport theory for neutrinos with parity violation and its applications to the physics of supernovae and magnetars.
3. Koutarou Kyutoku (Kyoto University): "Gravitational waves from binary-neutron-star mergers and the equation of state"
   Gravitational waves from binary-neutron-star mergers enable us to observe accurately the orbital evolution and postmerger dynamics. On the one hand, the orbital evolution is affected by the nature of moderately stiff matter characterizing premerger neutron stars. On the other hand, postmerger dynamics may reflect how nuclear matter transitions to quark matter at high density. In this talk, I will discuss the current status and future prospects.
4. Yui Hayashi (YITP, Kyoto University): "Higgs-confinement continuity in light of particle-vortex statistics"
   Some particular gauge theories with superfluidity, e.g., dense QCD, exhibit nontrivial Aharonov-Bohm (AB) phases around vortices, or anyonic particle-vortex statistics, in the Higgs regime. Recently, it has been under debate whether this nontrivial AB phase signifies the existence of a Higgs-confinement phase transition. In this talk, we address this question in favor of the Higgs-confinement continuity. By performing explicit calculations in the relevant lattice models, we elucidate how the calculated AB phase consistently aligns with the Higgs-confinement continuity, emphasizing the role of screening effects in the confining phase. This finding, in particular, supports the possibility of the quark-hadron continuity scenario.
5. Kentaro Nishimura (Hiroshima University): "Non-Abelian chiral soliton lattice in rotating QCD matter: Nambu-Goldstone and excited modes"
   The ground state of QCD with two flavors at a finite baryon chemical potential under rapid rotation is a chiral soliton lattice (CSL) of the $\eta$ meson, consisting of a stack of sine-Gordon solitons carrying a baryon number, due to the anomalous coupling of the $\eta$ meson to the rotation. In a large parameter region, the ground state becomes a non-Abelian CSL, in which due to the neutral pion condensation each $\eta$ soliton decays into a pair of non-Abelian sine-Gordon solitons carrying $S^2$ moduli originated from Nambu-Goldstone (NG) modes localized around it, corresponding to the spontaneously broken vector symmetry SU$(2)_{\rm V}$. There, the $S^2$ modes of neighboring solitons are anti-aligned, and these modes should propagate in the transverse direction of the lattice due to the interaction between the $S^2$ modes of neighboring solitons. In this paper, we calculate excitations including gapless NG modes and excited modes around non-Abelian and Abelian ($\eta$) CSLs, and find three gapless NG modes with linear dispersion relations (type-A NG modes): two isospinons ($S^2$ modes) and a phonon corresponding to the spontaneously broken vector SU$(2)_{\rm V}$ and translational symmetries around the non-Abelian CSL, respectively, and only a phonon for the Abelian CSL because of the recovering SU$(2)_{\rm V}$. We also find in the deconfined phase that the dispersion relation of the isospinons becomes of the Dirac type, {\it i.~e.~} linear even at large momentum.
6. Toru Kojo (Tohoku University): "Sound velocity peak and a dual model for cold, dense QCD"
   The recent neutron star observations indicate that the QCD equations of state (EOS) are soft-to-stiff type, i.e., EOS is soft at low density but evolves to very stiff EOS at high density. We discuss the origin of this disparity using a dual model of cold, dense QCD. The relationship between the negative trace anomaly and non-perturbative effects is also briefly discussed.
7. Masakiyo Kitazawa (YITP, Kyoto University): "Lee-Yang zeros around critical point of heavy-quark QCD"
   We explore the distribution of the Lee-Yang zeros around the critical point that appears in the heavy-quark region of QCD at nonzero temperature in lattice numerical simulations. With the aid of the hopping-parameter expansion that is valid around the critical point, our numerical analysis is capable of analyzing the partition function in the complex parameter plain with high accuracy. From the Lee-Yang zeros thus obtained, we study their scaling behavior and the edge singularity.

Topic contribution

1. Masaru Hongo (Niigata University): "Hydrodynamic theory with approximate symmetry"
   
2. Len Brandes (Technical University of Munich): "Inference of the neutron star matter equation of state"
   
3. Yuki Fujimoto (University of Washington) "Dense QCD EoS: Conformal limit and weak-coupling results"
   
4. Etsuko Itou (YITP, Kyoto U.) "Lattice results for the speed of sound in dense QCD-like theories"
   
5. Teiji Kunihiro (YITP, Kyoto U.) "Precursory soft modes of the QCD phase transitions and associated anomalous lepton-pair production"
   
6. Yoshimasa Hidaka (KEK) "Numerical simulation of dense QCD matter in (1+1) dimensions"
   
7. Yuya Tanizaki (YITP, Kyoto U.) "Confinement as SPT states and eta’ periodicity"
   
8. Zebin Qiu (Keio University) "Quasicrystal in QCD: Mixed Soliton of Pion and eta Meson"
   
9. Tetsuo Hatsuda (RIKEN iTHEMS) "Hyperon interactions from lattice QCD"
   
10. Asanosuke Jinno (Kyoto University) "Lambda-nucleon interaction in dense matter examined from heavy-ion collisions and hypernuclei"