The 22nd International Conference on QCD in Extreme Conditions

14 Jul 2026, 08:30 → 17 Jul 2026, 17:40 Asia/Seoul

Pukyong Convention Hall (Pukyong National University)

Seung-il Nam (Pukyong National University)

Welcome to XQCD 2026 and the XQCD 2026 PhD School

Conference

The International Conference on QCD in Extreme Conditions (XQCD) is a series of international workshop-style conferences, held annually, which brings together experts working on the theory and phenomenology of QCD under extreme conditions of temperature and/or baryon density, together with related topics.

The 22nd edition (XQCD 2026) took place at the Pukyong Convention Hall, Pukyong National University (PKNU), Busan, Republic of Korea, from July 14 to July 17, 2026.

The conference was co-hosted by CTPU/IBS, CENS/IBS, TOPTIER/IBS, KoALICE, OMEG. and IRST/PKNU. 

PhD School

The accompanying PhD School on QCD in Extreme Conditions took place from July 12 to July 13, 2026, at the CEO Hall Miraegwan, Pukyong National University (PKNU), Busan, Republic of Korea. Registration for the school was possible via the registration page of the XQCD 2026 conference.

Conference Topics

• QCD at Finite Temperature and Density
• Heavy Ion Collision Phenomenology
• Phase Diagram of Strongly Interacting Matter
• Properties of the Quark-Gluon Plasma
• Properties of Strongly Interacting Gauge Theories
• The Sign Problem in Lattice QCD
• QCD in External Fields
• Neutron Stars and Cosmology in QCD 
• New algorithmic developments in QCD
• New aspects of symmetries in QCD

Invited speakers

• Prof. Kai Zhou (The Chinese University of Hong Kong)
  Heavy-Ion Collision Phenomenology; New Algorithmic Developments in QCD
• Prof. Minjung Kweon (Inha University)
  Properties of the Quark–Gluon Plasma; Experimental Heavy-Ion Collisions
• Prof. Toru Kojo (KEK)
  Phase Diagram of Strongly Interacting Matter; Neutron Stars
• Prof. Volodymyr Vovchenko (University of Houston)
  Heavy-Ion Collisions; QCD Equation of State at Finite Density
• Prof. Yoshimasa Hidaka (YITP, Kyoto University)
  QCD Symmetries; Chiral Symmetry and QGP Properties
• Prof. Violetta Sagun (University of Southampton)
  Neutron Stars and Dense QCD Phase Transitions
• Prof. Chihiro Sasaki (University of Wroclaw)
  Effective QCD for extreme QCD
• Prof. Jana Günther (University of Wuppertal)
  Lattice QCD update for extreme QCD

 

 

xQCD2026 poster.pdf

Tuesday 14 July

Registration & Opening: Registration

Convener: Prof. Seung-il Nam (Pukyong National University)

Registration & Opening: Opening

Convener: Seung-il Nam (Pukyong National University)

Invited Talks: Session A

Convener: Seung-il Nam (Pukyong National University)

1 Non-perturbative perspectives on QCD thermodynamics

Speaker: Chihiro Sasaki (University of Wroclaw & SKCM2 at Hiroshima University)

XQCD.pdf

2 QCD phase diagram at finite baryon density from heavy-ion collisions and new expansions

Speaker: Volodymyr Vovchenko (University of Houston)

Vovchenko-XQCD-2026.pdf

10:50 Coffee break

Contributed Talks: Session A

Convener: Toru Kojo (KEK)

3 Bubble Nucleation and Hadronic Phase Conversion in an Expanding Quark–Gluon Plasma

We study the first-order chiral phase transition dynamics in a supercooled expanding quark–gluon plasma (QGP). Using the BEST equation of state incorporating a QCD critical point and constrained by lattice QCD data, we investigate how thermally nucleated hadronic bubbles grow and convert the surrounding QGP into hadronic matter during Bjorken expansion. We identify three characteristic time scales governing the phase-conversion dynamics: the onset of nucleation, rapid hadronic conversion, and completion of the transition. We find that the phase conversion generates a nontrivial distribution of thermodynamic states in the hadronic matter beyond smooth hydrodynamic evolution, which may leave observable imprints on final-state particle distributions in heavy-ion collisions.

Speaker: Noriyuki Sogabe (University of Osaka)

XQCD_noanimation.pdf

XQCD_with_animation.pptx

4 Deconfinement-Higgs continuity in SU(2) adjoint Higgs model at finite temperature

We investigate the finite-temperature phase structure of the four-dimensional SU(2) adjoint Higgs model, with particular emphasis on the possible deconfinement–Higgs continuity: the conjecture that the high-temperature deconfined phase of Yang–Mills theory and the finite-temperature Higgs phase belong to the same thermodynamic phase. We begin with an analysis of the global symmetries, showing that the Higgs and deconfined regimes are expected to exhibit the same symmetry pattern, in contrast to the confined phase. This observation supports the possibility of deconfinement–Higgs continuity, although it does not rule out a phase transition between the deconfined and Higgs phases that is unrelated to global symmetries. We further carry out a deformation analysis, which provides an explicit continuous path connecting the “deconfined symmetric” and “deconfined Higgs” regions in a reduced three-dimensional lattice model. Taken together, these results suggest that the Higgs and deconfined regimes can be continuously connected, while the confined phase remains separated from them.

Speaker: Masashi Kawahira (Yukawa Institute for Theoretical Physics, Kyoto University)

5 Lee-Yang zeros and edge singularity in an effective model of QCD

We investigate the distribution of Lee-Yang zeros in the complex chemical potential plane and their relation to the Lee-Yang edge singularity in a linear sigma model as an effective model of QCD. To treat finite-size systems in a mean-field approach, we define the partition function as an integral of the constant order parameter field, which allows a simultaneous treatment of Lee-Yang zeros in finite volume and the Lee–Yang edge singularity in the thermodynamic limit. We study the temperature dependence of the Lee-Yang zeros and demonstrate their behavior, especially near the critical point and vanishing chemical potential. We also compare our results with recent lattice QCD simulations.

Reference: T. Wada, G. Kovacs, M. Kitazawa, T.M. Doi, arXiv:2605.19964 [hep-ph]

Speaker: Masakiyo Kitazawa (YITP, Kyoto University)

260714XQCD_LYZ.pdf

6 Current Memory in the Dynamical Evolution of Critical Cumulants

Interpreting conserved-charge cumulants near the QCD critical point requires a dynamical description of how fluctuations evolve during the finite lifetime of the fireball. In this talk, I will focus on the conserved-charge diffusion sector and ask how non-Gaussian cumulants are modified when the diffusive current is allowed to retain memory, instead of being instantaneously slaved to the density gradient as in Fick’s law. This is motivated by the fact that, in an evolving medium, gradients and fluctuations change on finite time scales, so the current response need not be instantaneous. Using a Maxwell--Cattaneo-type extension of diffusion as a minimal framework, we study equal-time correlation functions and their mapping to finite-acceptance cumulants. The current relaxation time introduces a new dynamical scale that modifies the relaxation pattern of fluctuations and affects their imprint on experimentally relevant cumulants.

Speaker: Navid Abbasi (Lanzhou University)

12:30 Lunch

Contributed Talks: Session B

Convener: Su Houng Lee (Yonsei University)

7 Thermodynamics and Polyakov-Loop Potential in Accelerated Pure Gluonic Matter

In this talk, I will report our recent achievements on the thermodynamics of accelerated gluonic matter.

QCD Phase Transition under Acceleration
Various phases of QCD matter have been studied with external parameters such as temperature, density, magnetic field, and rotation. In this talk, I will discuss acceleration as another parameter for the confinement-deconfinement properties of gluonic matter. It is well known that the Minkowski vacuum state is perceived as a thermal state under acceleration, leading to a critical acceleration for the confinement-deconfinement phase transition. This observation motivates us to ask how finite-temperature QCD is modified in accelerated systems.

Thermodynamics in Accelerated Systems
We investigate the one-loop Polyakov-loop potential for accelerated pure gluonic matter. It is well known that there are subtleties in calculating the free energy or pressure in accelerated systems: multiple different results can be obtained with different calculation methods. Here, we calculated the free energy in three ways: direct calculation in the accelerated frame, calculation using the energy-momentum tensor (EMT) in the accelerated frame, and direct calculation after performing a conformal transformation to the optical frame. As a result, we demonstrated that the calculation using EMT in the accelerated frame agrees with the calculation in the optical frame, and we observed that the direct calculation in the accelerated frame corresponds to the pressure (which, in fact, differs from the negative of the free energy).
We also obtained the Polyakov-loop potential for the accelerated system. The potential becomes steeper as the acceleration increases, indicating that the system becomes more deconfined.

Speaker: Dr Yusuke Shimada (YITP, Kyoto University)

XQCD2026_0714.pdf

8 Hadron Thermodynamics in de Sitter Spacetime

We investigate the thermodynamics of a hadron gas in de Sitter spacetime using the hadron resonance gas model. QCD thermodynamics is sensitive to external environments because changes in the vacuum structure, hadron spectrum, and effective degrees of freedom can modify the thermodynamic behavior of the system. Curved spacetimes provide a particularly rich setting, since vacuum states and thermality can depend on the observer; in de Sitter spacetime, the Bunch-Davies vacuum is perceived as a thermal state by a static observer with the Gibbons-Hawking temperature. Motivated by this observer-dependent thermality, we study the temperature dependence of the energy density and entropy density within the causally accessible region of a static observer. We find that these quantities are dominated by vacuum contributions and geometric corrections associated with higher-spin fields. Our results indicate that the thermodynamics of hadronic matter in de Sitter spacetime is strongly governed by both vacuum structure and spacetime geometry, rather than by thermal excitations alone.

Speaker: Sho Yoshida (the University of Tokyo)

XQCD2026.pdf

9 Locating Roberge-Weiss Tricritical Point in Heavy-Quark QCD on the Lattice

The order of the phase transition in QCD is known to depend on the quark masses and the baryon chemical potential $\mu$. In the heavy-quark limit and at $\mu/T=i\pi/3$, the first-order Roberge-Weiss transition line terminates at a triple first-order point where three first-order lines merge. As the quark mass decreases, this triple point is expected to terminate at a tricritical point. Determining the location of this tricritical point is therefore an important subject for understanding the phase structure of heavy-quark QCD at imaginary chemical potential.

In this study, we investigate the location of the Roberge-Weiss tricritical point in the heavy-quark region in lattice QCD simulations. The simulations are performed using the hopping-parameter expansion, which enables high-statistical analyses over a wide range of heavy-quark masses. We use the Binder cumulant and related observables to analyze the finite-size scaling behavior and identify the change in the order of the transition. We also investigate the Lee-Yang zeros in the complex $\mu$ plane. Their approach to the imaginary axis in the thermodynamic limit provides information on the order of the transition and the associated critical behavior. Using these numerical results, we constrain the location of the tricritical point with significantly improved precision compared with previous studies and discuss the associated critical exponents.

Speaker: Tatsuya Wada (Kyoto University/YITP)

XQCD_wada.pdf

10 Extract the QCD speed of sound in the presence of quantum fluctuations

It has recently been realized that in the ultra-central heavy-ion collisions, mean transverse momentum of hadrons contains the information of the fundamental thermodynamic properties of quark-gluon plasma (QGP). In particular, in nucleus-nucleus collisions, the linear correlation between the mean transverse momentum and the charged multiplicity is attributed to the QCD speed of sound, which promotes both theoretical and experimental investigations. However, in realistic collisions, these studies suffer from the contamination of fluctuations, especially the quantum fluctuations from the initial state, which bias the extracted value. Traditional analyses struggle to separate this fluctuating background from the genuine thermodynamic signal.

In this talk, we present a systematic subtraction scheme to resolve this issue. In a thermalized QGP, the quantum fluctuations $\delta$ are independent from the thermodynamic responce and vary randomly across events. According to the Central Limit Theorem, the distribution of $\delta$ should approach Gaussianity allowing us to extract the physical speed of sound statistically even in the presence of these fluctuations. Crucially, this approach can also serve as a direct probe of QGP thermalization. In a non-thermalized system, the distribution of $\delta$ deviates from Gaussianity and the extracted value of speed of sound is non-physical. The deviations from thermalization can be quantified by the standardized kurtosis $\kappa_4$ of $\delta$.

Validated by the event-by-event hydrodynamic simulations, the extracted speed of sound in our framework is successfully consistant with the predictions from lattice QCD, from large to small collision systems. To enhance statistical robustness, we also employ AI-powered diffusion model for data augmentation, which further strengthen the reliability of our results.

Speaker: Yu-Shan Mu (Fudan University)

YSMu-XQCD2026.pdf

15:20 Coffee break

Contributed Talks: Session C

Convener: Di-Lun Yang (Academia Sinica)

11 Equation of state of hot and dense QCD using the complex Langevin equation

Non-perturbative lattice simulations have contributed significantly to our understanding of QCD at finite temperature. However, when applied to non-zero baryon density, lattice simulations face the infamous sign problem, preventing the straightforward application of established importance-sampling techniques. A possible way out is provided by the complex Langevin approach, which is based on the stochastic evolution of complexified degrees of freedom in an auxiliary time dimension. We present continuum-extrapolated results of the first complex Langevin simulations of QCD with physical pion masses, reaching high baryon densities but restricting to temperatures above the crossover. In particular, we have computed the QCD equation of state including the pressure, energy density, and various derived quantities. Moreover, we report on our recent efforts to better understand the problem of wrong convergence that complex Langevin simulations sometimes face and how existing correctness criteria compare against one another.

Speaker: Michael Mandl (University of Graz)

mandl_handout.pdf

mandl_presentation.pdf

12 Generative diffusion models for lattice field theory

Diffusion models are a widely used method in generative AI to produce images and videos. I will discuss the application to lattice field theory and the connection with methods known from theoretical physics, such as stochastic quantisation.

Speaker: Gert Aarts (Swansea University)

talkXQCD2026.pdf

13 Sampling Non-Abelian Lattice Gauge Theories with Diffusion Models

In the last few years, generative machine learning methods have been explored as possible alternatives to classic Markov chain Monte Carlo (MCMC) methods in lattice field theory. A key advantage being that generative models such as normalizing flows and diffusion models have by design no autocorrelation between generated samples. In this vein we have recently introduced gauge-equivariant diffusion models for lattice gauge theories. Using lattice gauge equivariant convolutional neural networks (L-CNNs) and the Metropolis-adjusted annealed Langevin scheme we are able to accurately sample 2D U(2) and SU(2) field configurations, and most recently also 4D SU(3) configurations. Additionally, our models extrapolate remarkably well to larger lattices and larger inverse couplings than originally trained with. We confirm this by comparing observables to analytically known values and to hybrid Monte Carlo results.

Speaker: Thomas R. Ranner (TU Wien)

xQCD26_Ranner.pdf

14 Quantum simulation of SU(2) gauge theory with staggered fermion

In recent years, real-time evolution based on the Hamiltonian formulation of lattice gauge theories has been investigated as an alternative framework that can circumvent the sign problem—a sampling inefficiency in quantum Monte Carlo methods arising from topological terms, chemical potentials, or real-time dynamics. With the rapid development of quantum computing, it is now plausible to handle the exponentially large Hilbert space of increasing gauge bosons.

To demonstrate the feasibility of this approach, we study the real-time simulation of SU(2) Yang-Mills theory on a (2+1)-dimensional lattice with staggered fermions. As a beginning of the entire blueprint ,we first classically emulate a digital quantum simulation of a (2+1) dimensional small lattice. By analyzing the entanglement growth between different spatial points and between gauge bosons and staggered fermions, we investigate the thermalization of the system. We also compute pair production and discuss its dependence on the choice of initial states.
Then, we also generalize our method to larger system which is a ladder lattice with periodic boundary condition. We exploit the periodic symmetry of the system to map the ladder lattice onto a spin system, and obtain the local Hamiltonian matrix for digital quantum simulation.

Speaker: Zhen-Xuan Yang (Fudan University)

15 The electric conductivity coefficient of magnetized QCD from the lattice

Obtaining the electric conductivity for out-of-equilibrium magnetized QCD mainly faces the challenge of a numerically ill-posed problem. This problem arises when extracting the spectral function from noisy Euclidean correlators on a finite lattice. Recently, a number of novel frameworks have been proposed to resolve the ill-posed problem, including, for instance, machine learning techniques. The small frequency behaviour of the spectral function obtained from these methods can be related to the electric conductivity coefficient via a Kubo formula. In this work, we study the electric conductivity coefficient at non-zero external magnetic fields for Wilson fermions in quenched lattice QCD. We account for systematic effects by using machine learning methods as well as other state-of-the-art spectral reconstruction methods to compute the electric conductivity.

Speaker: Christian Andratschke (Bielefeld University)

17:20 Poster Setup

Poster Session

16 Dark energy and QCD instanton vacuum in a Friedmann-Lemaître-Robertson-Walker universe

The standard model of the universe, λCDM, is based on the FLRW metric with a flat coordinate space and the Friedmann equations. The cosmological constant λ provides the cancellation of the matter field contributions in the flat (Minkowski) space, as was proposed long ago in 1967 by Zeldovich. The dynamical dark energy appears on the surface of the vacuum energy of matter fields at the flat (Minkowski) space. Within the Standard Model, the gluon Yang-Mills (YM) fields are playing a specific role since the properties of their vacuum, where there is the presence of the gluon condensate, provide the nonperturbative vacuum energy. It is natural to apply the successful instanton liquid model of the QCD vacuum and its lowest excitations. Our aim is to calculate the contribution of gluon YM fields to the dark energy density. We find that the universe metric is generating the QCD vacuum excitation, which gives the contribution to the dark energy density. But this one may hardly play a central role in the dynamics of the universe, since its timescale is too small. We also find the equation-of-state parameters $w_0=-1,w_a=0$ in accordance with λCDM, while the newest data give them $w_0 >-1,w_a\neq 0$. They are requesting a contribution from an ultralight scalar such as an axion, or from YM field topological configurations with the nontrivial holonomy due to the deviation from a pure de Sitter state [Van Waerbeke and Zhitnitsky, arXiv:2506.14182 [astro-ph.CO]].

Speaker: Mirzayusuf Musakhanov (Institute of Theoretical Physics, NUUZ, Uzbekistan)

17 Deep Learning Augmented Quasi-Particle Framework for Quarkonia Melting in QCD Matter

Understanding the non-perturbative properties of the quark-gluon plasma (QGP) formed in ultrarelativistic heavy-ion collisions remains a central challenge in QCD phenomenology. Conventional quasi-particle approaches rely on analytic parametrizations that often fail to capture the complex thermal structure of the medium, particularly near the deconfinement crossover region. To address this, we develop a deep-learning-assisted quasi-particle model (DLQPM) [1] in which residual neural networks are trained directly on lattice QCD thermodynamic data, enabling a robust, non-perturbative extraction of the temperature-dependent medium properties of the QGP without the assumptions inherent to perturbative frameworks.
The machine-learning-derived medium properties are employed to construct a complex-valued medium-modified Cornell potential that encodes both color screening and Landau damping effects, thereby driving the dissociation of heavy quarkonia in the deconfined medium. Heavy quarkonia, including charmonium (J/psi, psi(2S)) and bottomonium (Upsilon(1S), Upsilon(2S)), serve as important probes of QGP formation owing to their sequential suppression pattern experimentally observed at RHIC and LHC [2, 3], directly reflecting the temperature and density conditions of the created medium. The present framework offers a flexible, data-driven, and physically well-motivated path toward bridging first-principles lattice QCD constraints with quarkonium suppression measurements, with direct relevance to the ongoing heavy-ion programs at ALICE, CMS, and ATLAS.

References:
[1] M. Y. Jamal, F. P. Li, L. G. Pang and G. Y. Qin, Phys. Rev. C 113, 034915 (2026).
[2] T. Matsui and H. Satz, Phys. Lett. B 178, 416 (1986).
[3] S. Chatrchyan et al. (CMS Collaboration), Eur. Phys. J. C 72, 1945 (2012).

Speaker: Mohammad Yousuf Jamal (Central China Normal University, Wuhan, China)

18 Exotic Core Signatures in Neutron Stars from Spacetime Curvature within Modified Gravity

Neutron stars (NSs) are the superdense objects with exceptionally strong gravitational fields, providing an ideal laboratory for exploring general relativity (GR) in the high-curvature regime. They also open up exciting possibilities for probing new gravitational physics beyond the established framework of GR. Thus, investigating modified theories of gravity in the context of superdense stars is both fascinating and crucial for advancing our understanding of gravitational phenomena under such extreme environments. Energy-momentum squared gravity (EMSG) is a modified theory of gravity that extends GR by including nonlinear terms that involve the energy-momentum tensor $T_{\mu\nu}$. In this study, we investigate the effect of EMSG on the curvature of NSs by using three relativistic mean-field (RMF) equations of state (EOSs) and three hadron-quark phase transition (HQPT) EOSs. This study mainly focuses on the Kretschmann ($\mathcal{K}$) and Weyl ($\mathcal{W}$) curvature scalars. We have calculated the radial variation and variation with the baryon density of the curvature scalars by varying the free parameter $\alpha$. We observed a distinct and interesting behaviour of the curvature profiles near the phase transition region for the HQPT EOSs. These signatures may help us to probe the exotic core phases inside NSs.

Speaker: Mr Sayantan Ghosh (National Institute of Technology Rourkela)

19 Spectral Function Analysis of the Vector and Axial-vector Meson Correlators at Non-zero Temperature/Small Baryon Density in Lattice QCD

In the presence of the chiral symmetry, the vector and axial-vector meson channels are expected to be degenerate. With Generation 2 and Generation 2L FASTSUM lattice gauge field ensembles at non-zero temperature, the FASTSUM collaboration studied the mesonic/baryonic correlator ratios at finite temperature. They also studied the effect of small baryon chemical potential on the mesonic correlators using the Taylor expansion method. Here, using the Maximum Entropy Method (MEM), we reconstruct spectral functions of corresponding mesonic channels at non-zero temperature. These results are analyzed together with the respective correlators, augmented with leading-order terms in the Taylor expansion at small baryon chemical potential, to understand a possible origin of the degeneracy in the chiral symmetry restored phase. In this preliminary report, we discuss the systematic effects and motivate future studies on Generation 3 ensembles which have a finer temporal lattice spacing.

Speaker: Sol Noh (Sejong University)

SolNoh_2026_XQCD_v10.pdf

20 The in-medium properties of $D_s$ and $B_s$ mesons in hot and dense resonance matter

The impact of density and temperature on pseudoscalar $D_s$ and $B_s$ mesons is analyzed within an isospin-asymmetric resonance matter using the chiral SU(3) model combined with a QCD sum-rule approach. The quark and gluon condensates obtained from the chiral SU(3) model serve as input to the QCD sum rule approach, enabling the calculation of in-medium masses of $D_s$ and $B_s$ mesons. These effective masses are markedly altered by the presence of $\Delta$-resonance baryons in the medium, highlighting the strong sensitivity of $u$, $d$ and $s$ light quarks in mesons to the surrounding hot and dense hadronic environment. Therefore, a clear understanding of these effects is crucial for the precise interpretation of quark–gluon plasma signatures and can improve the analysis of future heavy-ion collision data from FAIR experiments such as CBM and PANDA.

Speaker: MANPREET KAUR (Dr. B R Ambedkar National Institute of Technology Jalandhar, Punjab, India)

21 Unraveling quark-level collectivity via $p_{\rm T}$-differential radial flow observable in Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV with the AMPT model

We investigate the $p_{\rm T}$-differential radial flow observable $v_0(p_{\rm T})$ in Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV using AMPT model in its String Melting (SM) configuration. For inclusive charged hadrons, the AMPT-SM framework, that includes partonic dynamics, reproduces three hallmarks of genuine collective behavior: (i) long-range pseudorapidity correlations, (ii) factorization of two-particle correlations into a single-particle $v_0(p_{\rm T})$, and (iii) a centrality-independent scaling of the normalized shape $v_0(p_{\rm T})/v_0$ at low-$p_{\rm T}$, in close analogy with established signatures of anisotropic flow. For identified hadrons ($\pi^{\pm}$, $K^{\pm}$, $p + \bar{p}$), $v_0(p_{\rm T})$ exhibits a clear mass-ordering at low-$p_{\rm T}$ and a characteristic meson-baryon separation at intermediate-$p_{\rm T}$. In central Au+Au collisions, the NCQ-scaled observable $v_0(p_{\rm T})/n_q$ follows a universal curve when plotted against $(m_{\rm T} - m_0)/n_q$, while this scaling is progressively violated toward peripheral collisions where the partonic phase becomes short-lived. Taken together, these findings extend the paradigm of partonic collectivity from anisotropic to isotropic flow and establish radial collectivity as a partonic-stage phenomenon.

Speaker: Rohit Agarwala (Department of Physics, Bodoland University)

22 Valence quark structure of proton in dense nuclear matter

The European Muon Collaboration (EMC) effect indicates that the nuclear medium is not merely a passive background but plays an active role in shaping the internal structure of nucleons, as the structure function of nucleons inside the nuclei comes out to be different from that of free nucleons. Motivated by the EMC effect, the present work focuses on the study of internal quark dynamics of the proton in symmetric nuclear matter. The quark structure is investigated through quark-quark correlator in the diquark spectator model by incorporating the medium effects via effective masses of proton, quarks and all feasible diquark systems, computed in chiral SU(3) quark mean field model.

Speaker: Ms Navpreet Kaur (Department of Physics, Dr. B R Ambedkar National Institute of Technology Jalandhar, Punjab-144008, India)

23 Capturing the Schwinger Effect at One Loop: A Resummed In-In Formalism in a Constant Electric Field

The Schwinger effect is a nonperturbative manifestation of vacuum instability and cannot be captured by a finite-order expansion in the external electric field. Its standard treatment already involves an appropriate resummation. For example, the vacuum decay rate is obtained in the in-out formalism from the imaginary part of the one-loop effective action, which compactly represents the sum of relevant one-particle-irreducible contributions in the background field.

The situation is more subtle in the in-in formalism. One may naively expect that the pair-production effect can be incorporated by computing a one-loop effective action along the closed-time path. However, because the in-in formalism involves 2 x 2 matrix propagators, such a direct calculation is technically involved and less transparent. Moreover, the physical targets in the in-in formalism are real-time expectation values of operators, rather than the vacuum persistence amplitude itself. Therefore, the techniques used in the in-out formalism cannot simply be transplanted to the closed-time path, and an efficient resummation scheme suited for real-time observables is required.

In this talk, we present such a resummation scheme for a spatially homogeneous and time-independent electric field. The key step is to recast the boundary wavefunctions into quadratic self-energy-like terms in the functional integration formalism. The resulting generating functional in the modified in-in formalism leads to propagators that resum the infinite diagrams necessary to capture the vacuum-instability effects. With these modified propagators, real-time expectation values can be computed through ordinary one-loop diagrams while already incorporating the Schwinger pair-production effect.

As an application, we compute the in-in expectation value of the vector current and show that a simple one-loop calculation with the modified propagators captures the pair-production effect.

This talk is based on JHEP 05 (2026) 139.

Speaker: Shuhei Minato (UTokyo)

24 Effects of a Brueckner-Hartree-Fock–corrected effective mass on speed of sound, conformality, and observables of dark matter–admixed neutron stars

We construct an equation of state describing cold and dense matter in the core of neutron stars which includes an admixture of fermionic dark matter and incorporates nucleon effective masses derived from the relativistic Brueckner-Hartree-Fock (BHF) many-body approach within a relativistic mean-field model. Such a BHF-informed mixed-model approach increases stellar compactness, with mass-radius configurations that are consistent with smaller, lighter pulsars. The model displays the expected nonmonotonic behavior of sound speed hinted at by neutron-star data and is closer to the conformal bound at maximum mass. We find that the model displays tension with bounds on heavier pulsars, suggesting that the hypothesis of an aggregated dark component in neutron stars needs further critical study.

Speaker: Arijit Das (Indian Institute of Science Education and Research Thiruvananthapuram)

25 Imprints of non-symmetric dark matter haloes on magnetars: a two-fluid perspective

We investigate the impact of dark matter on the structure and deformation of magnetars. We adopt a perturbative approach to model magnetic-field-induced deformation and assume that dark matter interacts with hadronic matter only through gravity. Under the assumption that dark matter is significantly softer than hadronic matter, we find that magnetic fields can indirectly influence the dark matter distribution via space–time deformation. We observe that the number of stars possessing a dark matter halo extending beyond the visible surface increases with both the dark matter fraction and the stiffness of the dark matter equation of state. As magnetic fields deform the star away from spherical symmetry, a non-symmetric dark matter halo can form outside the stellar surface. This deformation leads to discrepancies in the observed spin period P, its derivative P dot, and the emitted gravitational wave signals. The observed visible surfaces predict a lower period and gravitational wave strain than that with a dark matter halo. This can have interesting observational gravitational signatures unique to magnetars having a dark matter halo.

Speaker: Asit Karan (Indian Institute of Science Education and Research Bhopal, IISER Bhopal)

26 Pole structure of the T_cs resonance in a coupled-channel quark model with three-body force

We investigate the pole structure of the (T_{cs}) resonance in a coupled-channel quark model. The model space is separated into a compact four-quark sector (P) and a two-meson continuum sector (Q={DK,D^\ast K^\ast}). Compact seed states are calculated using constituent-quark Hamiltonians with two-body one-gluon-exchange interactions and possible instanton-induced or three-body two-gluon-exchange terms. The continuum sector includes the long-range part of the pion-exchange, while the compact-continuum transition is treated within a generalized non-orthogonal framework.

The physical pole positions are obtained by eliminating the continuum sector and solving the resulting energy-dependent pole equation on the appropriate Riemann sheets. We trace the pole trajectories as a function of the compact-continuum coupling strength and examine the roles of the (D^\ast K^\ast) threshold, the finite (K^\ast) width, and the compact seed structure. The seed-1 trajectory is found to be particularly sensitive to the (D^\ast K^\ast) channel and can be shifted toward the (T_{cs0}(2870)) energy region. We also find additional companion-like solutions, suggesting that non-orthogonality and hidden rearrangement components of the compact basis may play a nontrivial role in the coupled-channel pole structure.

Speaker: Jongheon Baek (Yonsei)

27 Probing Neutron-to-Dark-Matter Conversion with Multimessenger Neutron-Star Observations

Neutron stars provide a unique astrophysical laboratory for probing dark matter under extreme density and strong gravity. Motivated by dark-sector interpretations of the neutron lifetime anomaly, we investigate neutron-to-dark-matter conversion in dense neutron-star matter and its impact on the equation of state and stellar observables.

We model baryonic matter within a non-linear $\sigma$--$\omega$--$\rho$ relativistic mean-field framework and include a fermionic dark component with repulsive self-interactions. By probing the dark-particle mass and coupling parameter space, we study how neutron-to-dark-matter conversion modifies neutron-star masses, radii, and tidal deformabilities.

To reduce the dependence on the uncertain baryonic-matter equation of state, we perform the analysis using several reliable nucleonic equations of state rather than a single baseline model. Confronting the resulting stellar sequences with massive pulsars, gravitational-wave tidal constraints, and NICER mass--radius measurements allows us to identify dark-sector regions that are robustly excluded or remain compatible with current observations. Our results provide constraints on neutron dark-decay scenarios that are less dependent on the baryonic equation of state, connecting dark matter physics, the neutron lifetime anomaly, and supranuclear-density matter in neutron stars.

Speaker: Davood Rafiei Karkevandi (University of Wroclaw, Institute of Theoretical Physics)

28 Strong Coupling QCD using D-Wave Quantum Annealer

We present a hybrid classical quantum approach for simulating lattice QCD in the strong coupling regime using a quantum annealer. In this limit, lattice QCD can be reformulated in terms of color singlet degrees of freedom monomers subject to local constraints arising from Grassmann integration. This dual representation eliminates the gauge fields while retaining essential non perturbative features such as confinement. We map the constrained dual variables onto a quadratic unconstrained binary optimization (QUBO) problem compatible with the D-Wave quantum annealer, where the physical constraints are enforced through penalty terms. To mitigate current hardware limitations, we employ a sublattice based strategy: small lattice blocks are sampled on the annealer and then embedded into a Metropolis-Hastings update scheme. The quantum annealer generates non local update proposals, which can improve sampling efficiency and reduce autocorrelation compared with conventional local update methods. Benchmark studies for U(3) strong coupling QCD indicate improved decorrelation and acceptance rates. We also discuss possible extensions to SU(3) gauge theory and the inclusion of gauge corrections beyond the strong coupling limit, suggesting that quantum annealing may provide a useful component of hybrid computational frameworks for exploring non perturbative QCD.

Speaker: Seungyeob Jwa (Seoul National University)

29 The Experimental Feasibility Study of Multi-Particle Scattering

The QGP(Quark-Gluon Plasma) and the QCD phase transition from/to the hadronic phase are one of the hottest topics in high energy nuclear physics. In particular, the dense matter study via nuclei collisions at $\sqrt{s_\mathrm{NN}} \sim 5 - 10 \, \mathrm{GeV}$ is expected to bring more detailed information on the 1st order phase transition, whereas the hot matter study through nuclei collisions at LHC energies is actively being performed under the assumption of the higher order phase transition. Even though several experiments scanning collision energies in the range $\sqrt{s_\mathrm{NN}} \sim 5 - 200 \, \mathrm{GeV}$ search for signatures of the critical point in the QCD phase diagram, the constraints from the inverse relation between the collision energy (T) and the baryonic chemical potential ($\mathrm{\mu_{B}}$) bring the experimental limit of the binary collisions along the phase boundary. As a new alternative experimental method to reach the higher $\mathrm{\mu_{B}}$ region at the same collision energy, a feasibility study of the multi-particle collisions is introduced with using three radioactive alpha sources and GEANT simulations, which never describe interactions between dying particles. This poster presents a comparison of experimental results with simulation outputs and discusses methods to distinguish multi-particle ($n > 2$) interaction effects from binary-collision contributions.

Speaker: Yongjun Choi

30 Cooper Pairing Between Particles with Repulsive Interactions in the Cold, Dense 2-Flavour Symmetric QCD Phase

Much of the physics in the cold-dense region in the QCD phase diagrams are characterised by the formation of Cooper pairs on the Fermi surface. In two-flavour symmetric quark matter, a phase transition is expected to occur into the two-flavour colour superconducting (2SC) phase. A key feature of this phase is that certain quarks remain ungapped due to repulsive colour-symmetric interactions. However, it is well established that Cooper pairs can still form via higher-order perturbative effects in large angular momentum channels, even when the bare interaction is repulsive. We investigate this possibility in QCD by analysing the renormalisation group (RG) equations for the quark-quark interaction vertex at extreme densities, where the perturbative expansion is valid. We find that the favoured partial wave is the 3P2 channel, analogous to the neutron superfluid phase at intermediate densities. However, the BCS gap for these colour-symmetric quark pairs remains small.

Speaker: Conan Sakamoto (YITP)

31 Effects of a Brueckner-Hartree-Fock–corrected effective mass on speed of sound, conformality, and observables of dark matter–admixed neutron stars

We construct an equation of state describing cold and dense matter in the core of neutron stars which includes an admixture of fermionic dark matter and incorporates nucleon effective masses derived from the relativistic Brueckner-Hartree-Fock (BHF) many-body approach within a relativistic mean-field model. Such a BHF-informed mixed-model approach increases stellar compactness, with mass-radius configurations that are consistent with smaller, lighter pulsars. The model displays the expected nonmonotonic behavior of sound speed hinted at by neutron-star data and is closer to the conformal bound at maximum mass. We find that the model displays tension with bounds on heavier pulsars, suggesting that the hypothesis of an aggregated dark component in neutron stars needs further critical study.

Speaker: Arijit Das (Indian Institute of Science Education and Research Thiruvananthapuram)

32 Impact of Hexaquark H Particle on Compact Star Properties

We study the possible existence of the hexaquark H particle (uuddss) in neutron stars. Within the Chromomagnetic Interaction framework, the flavor-singlet H exhibits a mass of 2212.7 MeV. Using the relativistic mean-field model, we explore how H particle couplings influence neutron star structure. Our results indicate that H particles could persist as stable constituents, reducing the maximum mass and providing new insights into the dense matter equation of state.

Speaker: Xuhao Wu (Yanshan University)

33 Memory effect on the heavy quark dynamics in QGP medium

This work investigates heavy quark dynamics within the quark-gluon plasma (QGP) by incorporating memory effects through a generalized Langevin equation. We model time-correlated thermal noise with a power-law decay using a fractional differential equation based on the Caputo fractional derivative of order parameter (\nu ). To calculate the impact of memory, we systematically evaluate the momentum correlation, the time evolution of the average squared momentum, the average squared displacement, and the average kinetic energy. Furthermore, we analyze how memory affects the higher normalized central moments of the heavy quark transverse-momentum distribution. Our findings demonstrate that time-correlated thermal noise substantially alters heavy quark dynamics, highlighting the critical role of memory effects in modeling QGP evolution.

Speaker: Jai Prakash (Shanghai Jiao Tong University)

34 Quantum Geometric Correction to Crystalline Color Superconductor

Recent neutron-star observations and equation-of-state studies incorporating ab initio QCD constraints are placing increasingly stringent constraints on dense matter. In this context, homogeneous color superconductivity has attracted renewed phenomenological interest and has been actively studied in recent years.

On the other hand, inhomogeneous phases remain relatively less explored. Moreover, quantum-geometric effects, which have been actively studied in condensed-matter physics, have not yet been fully incorporated into the study of color superconductivity.

In this work, we combine these two directions and investigate how quantum-geometric corrections modify conventional crystalline color-superconducting phases. In particular, we focus on the dispersion relations of crystal phonons and quantitatively examine their possible impact on neutron-star phenomenology, including collective modes and vortex-pinning dynamics relevant to pulsar glitches.

Speaker: Shuhei Minato (UTokyo)

35 Topological susceptibility in isospin-asymmetric QCD

We study the effects of non-zero isospin density on the topological susceptibility in lattice simulations with $N_f = 2 + 1$ flavors of improved staggered quarks at multiple lattice spacings. To reduce lattice artifacts, we employ a generalization of the eigenvalue reweighting technique known from vanishing densities to non-zero isospin chemical potentials, using the (massive) singular values of the Dirac operator. The results are compared with predictions from chiral perturbation theory.

Speaker: Fynn Kleinehanding (Bielefeld University)

Wednesday 15 July

Invited Talks: Session B

Convener: Gert Aarts (Swansea University)

36 Cold, dense QCD for neutron stars

Speaker: Toru Kojo (KEK)

2026_0715_XQCD26_Busan.pdf

37 Phase structure of QCD at intermediate temperature and baryon density

The nature of QCD matter at intermediate temperature and baryon density—beyond the dilute hadronic phase but before the onset of weakly coupled quark matter—is still not well understood. Various theoretical scenarios have been proposed for this regime, including quarkyonic matter and the spaghetti of quarks with glueballs (SQGB), yet systematic theoretical control is difficult: perturbative and effective-theory methods lose reliability at intermediate coupling, and the sign problem blocks lattice Monte Carlo at finite baryon density. In this talk, I review recent theoretical developments on the phase structure and symmetry realization in this regime. As a concrete first-principles example, I discuss two-color, single-flavor QCD in (1+1) dimensions, studied via uniform matrix product states, which are free of the sign problem. This setup reveals chiral symmetry realization patterns, a gapless Tomonaga–Luttinger liquid phase, and an equation of state approaching free-quark behavior at high density, shedding light on the quarkyonic and SQGB scenarios for the broader QCD phase diagram.

Speaker: Yoshimasa Hidaka (YITP, Kyoto University)

Hidaka_2026_07_xQCD.pdf

10:30 Coffee Break

Contributed Talks: Session D

Convener: Etsuko Itou (YITP, Kyoto U.)

38 Phase Transition to Hyperon Matter in Neutron Stars using an Effective Model with Chiral Invariant Masses

The baryon mass originates from spontaneous chiral symmetry breaking and a chiral invariant mass. The chiral invariant mass of hyperons has not been sufficiently considered. In this study, we investigate the dependence of the density at which hyperons appear on their chiral invariant masses in neutron star matter. We employ SU(2)_L x SU(2)_R chiral symmetry and introduce the chiral invariant masses of hyperons independently of the chiral invariant mass of nucleons. We find that the Lambda baryon can emerge in neutron star when the chiral invariant mass is as large as the vacuum mass. Neutron star observations may therefore constrain the chiral invariant mass of Lambda baryon.

Speaker: Masayuki Kanazawa (Nagoya University)

XQCD.pdf

39 Scaling Properties and the Equation of State of Dense Matter in Neutron Stars

Understanding the equation of state (EOS) of dense matter inside neutron stars remains an important topic in modern nuclear physics and astrophysics. Recent multimessenger observations, especially gravitational-wave measurements from binary neutron-star mergers, together with X-ray timing and radio pulsar observations, have opened new opportunities for probing matter at supranuclear densities. In this talk, I will discuss recent progress in constraining the EOS of dense neutron-star matter through model-insensitive approaches based on relativistic stellar structure, including scaling properties associated with neutron-star mass, radius, and compactness. Particular attention will be given to the connection between astrophysical observables and the microscopic properties of dense matter in neutron-star cores, including the pressure, energy density, and sound-speed behavior at supranuclear densities. Possible implications for the maximum-mass configuration, the approach to the conformal limit, and the properties of matter in the innermost neutron-star core will also be briefly discussed.

Speaker: Bao-Jun Cai (Fudan University)

xQCD2026-talk-BJCai.pdf

40 Chiral symmetry restoration and hyperon suppression in neutron stars

The ``hyperon puzzle'' remains a fundamental challenge in nuclear astrophysics. We investigate hyperon emergence in neutron star matter using the $SU(3)$ parity doublet model with chiral representation $(3,\bar{3}) + (\bar{3},3)$. This framework naturally incorporates chiral symmetry restoration and provides a systematic description of baryon masses in dense matter through the interplay between the chiral condensate and the chiral invariant mass $m_0$. We find that the hyperon onset density exhibits strong sensitivity to $m_0$: for $m_0 = 500$ MeV, hyperons first appear at $1.9n_0$ while for $m_0 \gtrsim 750$ MeV, hyperons emerge only above $5n_0$. This delayed onset arises from the weakened density dependence of baryon masses at larger $m_0$ values. When the hyperon onset density exceeds the expected quark-hadron transition range ($2$--$5n_0$), matter undergoes deconfinement before hyperons populate, avoiding the EoS softening while maintaining consistency with massive neutron star observations. Our results demonstrate that chiral dynamics provides a natural resolution to the hyperon puzzle without requiring ad hoc repulsive hyperon interactions.

Speaker: Bikai Gao

41 Direct Urca and Synchrotron Neutrinos from Magnetized Quark Matter

This talk reviews neutrino emission mechanisms in dense quark matter under strong magnetic fields, focusing on direct Urca and synchrotron processes and the role of Landau-level quantization. It highlights the resulting anisotropic and oscillatory emissivity and discusses implications for magnetar cooling and pulsar kicks.

Speaker: Igor Shovkovy (Arizona State University)

Direct Urca and synchrotron neutrinos from magnetized quark matter

42 Interacting mesons as degrees of freedom in a chiral model

We study the equation of state of hot and dense hadronic matter using an extended chiral mean field (CMF) model framework where the addition is the inclusion of interactions of thermally excited mesons. This is implemented by calculating the in-medium masses of pseudoscalar and vector mesons, obtained through the explicit chiral symmetry-breaking and vector-interaction terms in the Lagrangian, respectively, prior to applying the mean-field approximation. As a result, the in-medium meson contributions generate a feedback term to the CMF’s equations of motion, which then modifies the equation of state. With this improvement, we quantify the effect on the equation of state of strongly interacting matter through comparisons with state-of-the-art lattice QCD results and other hadronic models like the hadron resonance gas model. We find that the results of the updated hadronic CMF model with an improved meson description (mCMF) provide a better agreement with lattice-QCD data for thermodynamic state variables across a wide range of temperatures and baryon chemical potentials.

Speaker: Veronica Dexheimer (Kent State University)

DexheimerXQCD.pdf

12:30 Lunch & IAC Meeting

14:30 Conference Photo - PKNU park

15:00 Excursion

Thursday 16 July

Invited Talks: Session C

Convener: Masakiyo Kitazawa (YITP, Kyoto University)

43 Discriminative and Generative AI Exploration of QCD Matter

Speaker: Kai Zhou (Chinese University of Shenzhen, Hong Kong)

44 Properties of the Quark–Gluon Plasma;

Speaker: MinJung Kweon (Inha University)

10:30 Coffee Break

Contributed Talks: Session F

Convener: Chris Allton (Swansea University)

45 Color Randomization of $c\bar{c}$ System by Strong Color Fields in Relativistic Heavy-Ion Collision

Chamonium has recently attracted attention as a hard probe for imprints of the glasma, a non-equilibrium state of strong gluon fields forming in the early stage of a relativistic heavy-ion collision.

In this work, we investigate color randomization of the $c\bar{c}$ system induced by the glasma environment, focusing particularly on singlet-to-octet transition processes. The resulting octet state is expected to dissociate in the medium, which may affect the final charmonium yield observed in experiments.

In this talk, we first derive the evolution equation for the charmonium density matrix under the glasma. We then apply a singlet-octet projection approximation and solve the equation semi-analytically. Finally, we present results showing on what timescale and to what extent these transitions are induced by the glasma.

Speaker: Hidefumi Matsuda (Zhejiang University)

Color Randomization of cc ̅ System by Strong.pdf

46 Nonperturbative particle production and evolution in the dynamic Glasma

We have developed a new numerical model to tackle an important problem of heavy-ion physics: the missing link between the pre-equilibrium Glasma and the resulting quark gluon plasma (QGP) stage. Our model simulates the nonperturbative production and real-time dynamics of the quarks from the Glasma. In this presentation, we will introduce our model and report on the role of particle production in the thermal and chemical equilibration that leads to the initial conditions of the QGP.

The Glasma is modeled by the classical Yang-Mills equation on a real-time lattice. During the time evolution, the strong color fields are sampled and quarks are produced via the Schwinger mechanism. This mechanism is a nonperturbative effect, which cannot be captured by perturbative mechanisms such as those considered in effective kinetic-theories. After being produced, the quarks are evolved according to Wong's equations using a colored particle-in-cell algorithm. Then, we construct initial conditions for the QGP from the obtained particle distribution, which includes various physics information that has been missing from previous studies. This includes the initial inhomogeneities of electric charge and spin that originate from the quarks. These initial conditions are of particular importance for calculating experimental observables like electromagnetic probes and searching for the chiral magnetic effect (CME) in heavy-ion collisions.

Speaker: Nicholas J Benoit (Academica Sinica)

47 Chapman-Enskog calculation of the shear viscosity of quark-gluon plasma at finite temperature

We use the Chapman-Enskog method to investigate the shear viscosity of a quark-gluon plasma at finite temperature with a focus on its relation to parton cross sections. We use the recent analytical expression for the shear viscosity [1] of a massless quark-gluon gas at chemical equilibrium with Boltzmann statistics after including all $2\leftrightarrow 2$ parton scatterings. Applying the expression to scattering cross sections at finite temperature that are based on perturbative-QCD and screened with scaled thermal masses $m_D$ and $m_F$, we calculate the corresponding shear viscosity. We find [2] that our Chapman-Enskog results on $\eta g^4/T^3$ versus $m_D/T$ are similar to but higher than the leading-order results from the AMY framework. We also show that the shear viscosity-to-entropy density ratio $\eta/s$ is very sensitive to the choice of the momentum scale $Q$ used in the strong coupling, where a smaller $Q/T$ leads to a lower $\eta/s$ value. These results lay the foundation for mapping parton cross sections to given shear viscosity in parton transport models and QCD effective kinetic theory.

[1] O. Ohanaka and Z.W. Lin, Shear viscosity of a massless quark-gluon gas in chemical equilibrium in terms of all $2\leftrightarrow 2$ cross sections, arXiv:2602.08155 [hep-ph].
[2] O. Ohanaka and Z.W. Lin, Chapman-Enskog calculation of the shear viscosity of quark-gluon plasma including all $2\leftrightarrow 2$ scatterings at finite temperature, arXiv:2604.25059 [nucl-th].

Speaker: Zi-Wei Lin (East Carolina University)

eta-Lin.pdf

48 Recent PHENIX Highlights from RHIC

The PHENIX experiment at the Relativistic Heavy Ion Collider has carried out a broad and systematic program to study strongly interacting matter over a wide range of collision systems and beam energies. Although PHENIX completed data taking in 2016, its high-statistics data sets continue to provide important constraints on the properties of the quark-gluon plasma, the role of initial-state and cold-nuclear-matter effects, and the emergence of collectivity in small and large collision systems.

In this talk, we will present recent PHENIX highlights relevant to QCD matter under extreme conditions. We will discuss selected measurements of electromagnetic probes, heavy flavor, quarkonia, strangeness production, and identified hadrons in $p$+$p$, small-system, and $A$+$A$ collisions at RHIC energies. These measurements provide complementary sensitivity to different stages of the collision evolution, from initial-state nuclear effects and particle production mechanisms to the hot and dense medium formed in heavy-ion collisions. Particular emphasis will be placed on observables such as nuclear modification factors, azimuthal anisotropies, particle yields, and system-size and multiplicity dependence, which together constrain parton energy loss,
heavy-quark transport, hadronization mechanisms, and collective dynamics.

We will also discuss how the latest PHENIX results connect measurements across collision systems, beam energies, rapidity regions, and particle species. These results demonstrate that the PHENIX legacy data remain an active source of quantitative constraints on QCD matter at RHIC energies. They provide a coherent experimental foundation for understanding the formation and properties of strongly interacting matter, while offering important reference points and complementary constraints for ongoing analyses of recently collected sPHENIX data.

Speaker: maya shimomura (NWU/TOHOKU Univ. RARiS)

12:10 Lunch

Contributed Talks: Session G

Convener: Seyong Kim (Sejong University)

49 Color electric field correlators and quarkonia decay in QGP

For quark-antiquark separation $r \ll 1/T$, the interaction of a
quarkonium with a quark-gluon plasma medium can be approximated by a
dipole interaction with a color electric field. The evolution and decay
of the quarkonia in the plasma can then be calculated from transport
coefficients calculated from the thermal correlator of color electric
fields connected by an adjoint Wilson line.

We present a lattice calculation of these correlators in a
gluon plasma. We will study the structure of the correlator and the spectral
function, and extract the relevant transport coefficient.
We will also compare the correlator with the closely related one used for
the study of heavy quark diffusion coefficient.

Speaker: Saumen Datta (Tata Institute of Fundamental Research)

50 The influence of heavy quark potential on quarkonium formation in QGP

The Remler formalism provides a framework for the Wigner projection of a two-particle state onto bound states. This projection is implemented either at the onset of bound-state formation or during in-medium scattering of one of the constituent particles. This approach has been successfully applied to quarkonium production in both box simulations and heavy-ion collisions.

In the present study, the formalism is extended to strongly bound states with substantial binding energies by explicitly incorporating the potential energy between heavy quark pairs in the quark–gluon plasma (QGP).

Our results indicate that an attractive heavy-quark potential significantly enhances quarkonium production. Furthermore, the results are consistent with those obtained from statistical models in box simulations, provided that an appropriate spatial cutoff is introduced in the potential to effectively account for quantum effects.

Speaker: Taesoo Song (GSI)

The influence of heavy quark potential on quarkonium.pdf

51 Flow of the J/ψ and ψ(2S) in heavy ion collisions

We discuss the elliptic and triangular flow of the J/ψ and the ψ(2S) in relativistic heavy ion collisions based on the coalescence model. Starting from the investigation of their production from the quark-gluon plasma by regeneration, we evaluate their anisotropic flow based on their yield distribution as functions of transverse momenta. We incorporate the transverse momentum distribution of charm quarks by combining the Tsallis distribution with the blast wave model to take into account the spatial dependence of the phase distribution. We show different elliptic and triangular flow for the J/ψ and ψ(2S), and argue that the wave function distribution of charmonium states plays a significant role, presenting plausible explanations for the measurements by the CMS Collaboration on elliptic flow of the J/ψ and ψ(2S).

Speaker: Sungtae Cho (Kangwon National University)

52 Heavy-flavor probes of isotropization in small systems

In this work, we employ heavy-flavor (HF) jet tomography to probe the short-lived far-from-equilibrium medium created in proton-proton collisions at LHC energies. On an event-by-event basis, HF quark pairs produced in hard scattering via PYTHIA are embedded into a color string model and interact with the evolving medium through both collisional (based on Thoma-Gyulassy elastic cross-section) and radiative (DGLV in-medium gluon emission) energy-loss mechanisms. By analyzing the momentum modifications of charm and bottom quarks, we find that energy loss strongly depends on the degree of medium isotropization. The resulting final-state HF hadron spectra are contrasted with predictions from equilibrated QGP models such as EPOS4HQ.

Speaker: Daria Prokhorova (Tsinghua University)

Prokhorova.pdf

53 Non-equilibrium approach to heavy-quark transport

We discuss the non-equilibrium Green’s function approach to heavy-quark transport based on the Kadanoff-Baym equation. Using hard-thermal-loop perturbation theory, the self-energy terms are calculated up to next-to-leading order. In the on-shell limit, the kinetic equation reduces to a Boltzmann equation that accounts for elastic scattering and gluon emission from a single scattering. Numerical results indicate that the off-shell and memory effects in quark-gluon plasmas influence heavy-quark transport, particularly near the critical temperature.

Speaker: Juhee Hong

15:10 Coffee Break

Contributed Talks: Session H

Convener: Jon-Ivar Skullerud (Maynooth University)

54 The polarization of thermal dileptons at the next-to-leading order QCD

Dileptons are penetrating probes for the early-stage dynamics of the quark-gluon plasma (QGP). The polarization of dileptons encodes detailed information about their production mechanism. This study presents an integrated and realistic framework for calculating dilepton polarization signatures using the photon spectral function of a finite-temperature QCD plasma. Combining virtual photon spectral functions with a multi-stage iEBE-MUSIC hydrodynamic simulation of Pb+Pb collisions at the LHC, we focus on invariant masses < 5 GeV and confirm significant differences in polarization coefficients between next-to-leading order (NLO) [1] and leading order (LO) in the strong coupling [2]. We examine how these coefficients vary across reference frames and include the contribution from the NLO Drell-Yan process, an irreducible pQCD background [3]. Finally, we demonstrate how non-equilibrium modifications of the photon spectral function can impact dilepton polarization signatures, and present results including shear-viscous corrections to the polarization observables [4].

Speaker: Han Gao (McGill University)

xqcd-4.pdf

55 Probing Strong Magnetic Fields with Photons and Dileptons

Electromagnetic probes provide a unique window into the extreme environments created in heavy-ion collisions. This presentation reviews our recent theoretical evaluations of photon and dilepton production using quantum field theory. We highlight anomalous signatures resulting from the coupling of EM probes to intense magnetic fields, offering insights into the topological and dynamical properties of the hot, dense medium.

Speaker: Prof. xinyang wang (Anhui University of Science & Technology)

22thXQCD_Xinyang_m1.pdf

56 Fate of chiral and axial $U(1)$ symmetries in hot QCD matter under background magnetic fields

Understanding how external magnetic fields affect chiral symmetry and the axial anomaly is an important question in QCD under extreme conditions. At vanishing magnetic field, the light-quark chiral condensate serves as the standard order-parameter-like observable for chiral symmetry breaking, while the restoration of chiral $SU(2)_L\times SU(2)_R$ symmetry and the effective restoration of $U(1)_A$ symmetry can also be characterized through degeneracy patterns among scalar and pseudoscalar mesonic correlators. In a background magnetic field, however, this familiar picture has to be revisited. Since up and down quarks carry different electric charges, the magnetic field explicitly breaks isospin symmetry and induces different responses in the light-quark condensates. As a result, the conventional mesonic partner relations are modified, and one must carefully identify which mesonic channels and susceptibility differences provide proper probes of chiral symmetry restoration and the $U(1)_A$ anomaly in this case.

In this talk, I will first discuss the status of chiral and axial symmetries in nonzero magnetic fields, with particular attention to the role of light-quark condensates and mesonic susceptibility differences. I will then present an analysis of which observables remain suitable diagnostics of chiral symmetry restoration and of the $U(1)_A$ anomaly in the presence of magnetic-field-induced flavor breaking. Based on this theoretical consideration, I will present lattice-QCD results in $(2+1)$-flavor QCD using the highly improved staggered quark action. The calculations are performed at a fixed lattice spacing with a physical strange quark mass and light quark masses corresponding to $m_\pi\simeq 220~\mathrm{MeV}$, over a wide range of temperatures and background magnetic fields. The results provide insight into how the hierarchy and pattern of chiral and $U(1)_A$ symmetry restoration are modified by external magnetic fields.

Speaker: Dan Zhang

Danzhang_xQCD2026.pdf

57 Recent developments in spin hydrodynamics

In my talk, I will give a comprehensive overview of our group's recent results in spin hydrodynamics, including:
- generalized thermodynamic relations [1],
- the twofold expansion, in spin polarization and in gradients [2],
- stability and causality [3, 4],
- boost-invariant solutions [5, 6, 7],
- the new local equilibrium Wigner function for spin-1/2 particles [8, 9],
- discussion of Fermi-Dirac [10, 11] and Bose-Einstein statistics,
- extension of the spin hydrodynamics framework to spin-1 particles [12],
- preliminary numerical solutions of dissipative spin hydrodynamics, with transfer between the orbital and the spin part of the total angular momentum.
[1] W. Florkowski, M. Hontarenko, Phys.Rev.Lett. 134 (2025) 8, 082302.
[2] ZD, W. Florkowski, M. Hontarenko, Phys.Rev.D 110 (2024) 9, 096018.
[3] ZD, W. Florkowski, V. Mykhaylova, Phys.Rev.D 112 (2025) 5, L051901.
[4] S. Bhadury, ZD, W. Florkowski, S. K. Kar, V. Mykhaylova, Phys.Rev.D 113 (2026) 3, 036017.
[5] ZD, W. Florkowski, N. Lygan, R. Ryblewski, Phys.Rev.C 111 (2025) 2, 024909.
[6] ZD, N. Lygan, arXiv:2604.17392 [hep-ph].
[7] ZD, W. Florkowski, J. Witkowski, arXiv:2605.01857 [hep-ph].
[8] S. Bhadury, ZD, W. Florkowski, S. K. Kar, V. Mykhaylova, arXiv: 2505.02657 [hep-ph].
[9] ZD, Phys.Lett.B 873 (2026) 140205.
[10] ZD, Physics 7 (2025) 3, 31.
[11] S. K. Kar, V. Mykhaylova, arXiv:2511.09580 [quant-ph].
[12] W. Florkowski, S. K. Kar, V. Mykhaylova, arXiv: 2602.00819 [nucl-th].

Speaker: Zbigniew Drogosz (Jagiellonian University in Krakow)

58 Local spin polarization by color-field correlators and momentum anisotropy

We study the local spin polarization of quarks induced by color-field correlators stemming from the correlation of chromo-Lorentz force and chromo-magnetic polarization or chromo-spin Hall effect in the presence of momentum anisotropy. Such effects can trigger longitudinal polarization from fluctuating color fields in glasma or quark gluon plasma phases with transverse expansion for relativistic heavy ion collisions. Especially, from the glasma effect, the resulting longitudinal polarization spectrum of $\Lambda/\bar{\Lambda}$ hyperons has a sinusoidal structure with twice the azimuthal angle relative to the anisotropic direction. An order-of-magnitude estimate of the effect aligns with experimental observations. Our findings highlight the significant role of coherent gluon fields as a novel source for spin polarization phenomena in high-energy nuclear collisions.

Speaker: Haesom Sung (Academia Sinica)

17:30 Free Time

18:30 Conference Dinner

Friday 17 July

Invited Talks: Session D

Convener: Kazuya Mameda (Tokyo University of Science)

59 Neutron Stars, Quark Matter, and Physics Beyond the Standard Model

Speaker: Violetta Sagun (University of Southampton)

xQCD2026_Sagun.pdf

60 Exploring the Phase Diagram with Lattice QCD

Speaker: Jana N. Guenther (University of Wuppertal)

10:30 Coffee Break

Contributed Talks: Session I

Convener: Kai Zhou (Chinese University of Shenzhen, Hong Kong)

61 The axion-photon coupling from lattice Quantum Chromodynamics

The axion is a prime dark matter candidate that aditionally solves the strong CP problem. Its experimental detection relies on the axion-photon coupling, which receives a model-independent contribution from Quantum Chromodynamics (QCD). Previously, this contribution was only estimated via different variants of Chiral Perturbation Theory (ChPT) with inconsistent results. We present the first non-perturbative, first-principles determination of the QCD axion-photon coupling using continuum-extrapolated lattice simulations. We obtain $g_{a\gamma\gamma}^{\rm QCD}= -1.77(8)\alpha_{em}/(2\pi f_a)$, which is about 10% smaller in magnitude than the ChPT prediction quoted by the PDG. In this talk we will describe how this quantity can be extracted by studying the response of the QCD vacuum to a time-reversal violating combination of electromagnetic fields and discuss how our result modifies the constraints over the landscape of viable axion models, providing guidance for ongoing and future experimental searches.

Speaker: Dr José Javier Hernández Hernández (Central China Normal University)

XQCD2026_javi.pdf

62 Nuclear liquid-gas transition in strong coupling QCD

Strong coupling lattice QCD provides an effective framework for studying finite density QCD and the nuclear liquid–gas transition using dual degrees of freedom such as monomers, dimers, and baryon worldlines. In this representation, the sign problem is significantly reduced, enabling direct investigations of strongly interacting matter at low temperatures and finite baryon density.
However, the low temperature regime remains numerically very expensive. The worm algorithm suffers from rapidly increasing autocorrelation times, poor tunneling between metastable states, and inefficient sampling near the first order nuclear liquid-gas transition. These limitations make it difficult to explore the deep low temperature region and reliably determine the phase structure.
In this talk, I will introduce a new sampling strategy designed to overcome these limitations. The method employs nonlocal updates while simultaneously satisfying the local constraints of the dual variables through sublattice sampling techniques, aiming to improve efficiency in regimes where worm updates become ineffective. I will discuss the basic formulation of the method in the strong-coupling dual representation and its possible application to low temperature and finite density QCD systems.

Speaker: Jangho Kim (Seoul National University)

main.pdf

63 The fate of the U(1)-axial symmetry and the static quark potential at high temperature

The classical U(1) axial symmetry of the QCD lagrangian is broken by the quantum anomaly, but may be effectively restored at high temperature. Whether or not this effective restoration coincides with the chiral transition has been the subject of much debate. Both chiral and axial symmetries can be investigated through degeneracies of mesonic correlators and their associated susceptibilities. We present results for vector--axial-vector and scalar--pseudoscalar degeneracies from anisotropic lattice ensembles generated by the FASTSUM collaboration. We find evidence that the $U(1)_A$ symmetry is effectively restored at $\sim300$ MeV, well above the chiral transition temperature.

We also present results for the static quark potential using several different methods (BR spectral reconstruction, UV subtracted gaussian and lorentzian fits, and the Bala-Datta method). We find clear evidence of screening in the real part of the potential at very high temperature, but no agreement between the different methods at intermediate temperatures.

Speaker: Jon-Ivar Skullerud (Maynooth University)

xqcd26_skullerud.pdf

64 Hadron spectroscopy of QC2D at finite density

We investigate the chemical-potential dependence of hadron spectra in two-color QCD using the first-principles lattice simulations.
In this work, we compute two-point correlation functions for various hadrons by newly including the contributions from disconnected diagrams, and extract the corresponding effective masses.
In the meson sector, the mass hierarchy in the hadronic phase (normal vacuum) is found to be $m_\pi \lesssim m_{\eta} < m_\sigma \mathrm{(noisy)} < m_\rho \sim m_\omega \ll m_{a_1}$, which is similar to that in three-color QCD.
In the superfluid phase, this hierarchy is modified, and with increasing density it changes to $m_\sigma \mathrm{(noisy)} < m_{a_1} < m_\rho < m_\pi \sim m_{\eta} \mathrm{(noisy)} \ll m_{\omega} \mathrm{(noisy)}$.
In the diquark sector, the ordering remains as $m_{NG} \lesssim m_{I=0, S} < m_{I=1, AV} < m_{I=0, PS} \lesssim m_{I=0, V}$ in both phases, and the Nambu–Goldstone mode associated with spontaneous breaking of $U(1)_B$ is confirmed to be nearly massless.
Furthermore, by comparing correlators of chiral partners, we find indications of chiral symmetry restoration at high density.

Speaker: Etsuko Itou (YITP, Kyoto U.)

2026-07-xQCD.pdf

65 Centre vortices in thermal QCD: evidence of an intermediate “phase”

A study of centre vortices is presented on anisotropic, dynamical QCD lattices from the FASTSUM collaboration. Results are discussed across a broad sweep of temperatures up to >500 MeV. Centre vortex percolation, connectivity and other properties are analysed, supporting the existence of an intermediate QCD “phase” above Tc that maintains confinement.

Speaker: Chris Allton (Swansea University)

12:30 Lunch

Contributed Talks: Session J

Convener: Veronica Dexheimer (Kent State University)

66 Chiral Symmetry Breaking in Accelerating and Rotating Frames

In heavy-ion collisions, strong acceleration can generate an effective temperature via the Unruh effect, $T_U = a/2\pi$, which may reach the QCD scale. We study chiral symmetry breaking under acceleration and rotation using effective models. The predicted phase diagram depends on the renormalization scheme: subtracting the Rindler vacuum renders the critical temperature acceleration-independent, while subtracting the Minkowski vacuum enhances the critical temperature. With both acceleration and rotation present, the critical acceleration for chiral restoration decreases with angular velocity. This reveals that acceleration acts like a heat bath and rotation like a chemical potential, cooperatively suppressing the chiral condensate.

Speaker: zhibin zhu (Fudan University)

zhibinzhu.pdf

67 Vorticity-induced effects from Wess-Zumino-Witten terms

It was shown recently that vorticity manifesting from space-time torsion can be treated as an effective axial gauge field coupled to Dirac fermions in a flat spacetime. Motivated by this, we investigate the anomalous effects induced by vorticity, magnetic fields and chemical potentials on Nambu-Goldstone modes. Starting from a linear sigma model, I shall outline how to derive the Wess-Zumino-Witten effective action in the presence of external vector, axial-vector, and pseudo-scalar fields using a derivative expansion of the fermionic determinant. From this effective action, I will point out a new anomalous term that involves charged pions and vorticity. I will then briefly discuss the possible phenomenological implications of this new term.

Speaker: Geraint Evans (Institute of Physics, Academia Sinica)

Vorticity_induced_effects_from_Wess_Zumino_Witten_terms___XQCD_17th_July_2026_.pdf

68 Spatial confinemement/deconfinement transition in rotating and accelerating QGP

Quark-gluon plasma created in heavy-ion collision experiments is affected by relativistic rotation and strong acceleration, which influence its properties. In this report, we present the results of lattice investigation into how the confinement/deconfinement phase transition in gluodynamics is affected by rotation and acceleration. Specifically, we find that under the influence of these effects, the finite-temperature confinement/deconfinement phase transition becomes a spatial crossover. That is, spatially separated confinement and deconfinement phases can coexist within certain ranges of thermodynamic parameters. Additionally, we explore the properties of this transition.

Speaker: Victor Braguta (JINR)

report.pdf

69 Capturing the Schwinger Effect at One Loop: A Resummed In-In Formalism in a Constant Electric Field

Speaker: Shuhei Minato (The University of Tokyo)

xQCD-Korea.pdf

70 Effective-model analysis of topological susceptibility and meson susceptibilities in hot and dense matter

The behavior of the U(1) axial anomaly under extreme conditions is an important issue for understanding the QCD phase structure and the properties of hadrons. In particular, the topological susceptibility characterizes the strength of U(1) axial symmetry breaking, and its relation to chiral symmetry restoration in hot and dense matter has been extensively discussed.
Based on the Ward–Takahashi identities, the topological susceptibility can be expressed in terms of meson susceptibilities. Using this expression, we analyze its behavior at finite temperature and density within simple chiral effective models. We show that the topological susceptibility decreases with the restoration of chiral symmetry. Based on this result, we discuss the relation between chiral symmetry restoration and U(1) axial symmetry restoration within the framework of the effective model.

Speaker: Mamiya Kawaguchi (Anhui University of Science and Technology)

2026_XQCD_MK.pdf

15:40 Coffee Break

Contributed Talks: Session K

Convener: Yoshimasa Hidaka (YITP, Kyoto University)

71 Quantum-Metric Dominance in the Meissner Mass of Magnetized Color Superconductors

Quantum geometry is a prominent concept in modern physics. In particular, the Riemannian metric in Hilbert space, called the quantum metric, is an essential ingredient to realize superconductivity in flat-band systems where conventional kinetic dynamics are quenched, making quantum-geometric phenomena one of the most exciting fields in the recent condensed matter community. In this talk, we show that such intriguing physics induced by the quantum metric also plays a crucial role in dense QCD matter under external magnetic fields. We analytically reveal that in the two-flavor color-superconducting state, the Meissner mass transverse to the magnetic field is dominated by the quantum metric of Landau levels. Remarkably, in the strong field limit, the scaling of such a transverse Meissner mass is topologically bounded at the pairing gap squared, which is a sharp contrast to the scaling by chemical potential in the color-flavor locking state. This characteristic scaling in the transverse responce leads to a potential microscopic basis for surviving low-frequency quasi-periodic oscillations in magnetar asteroseismology, providing a novel connection from condensed matter physics and QCD to astrophysics and cosmology.

Speaker: Kazuya Mameda (Tokyo University of Science)

mameda_XQCD2026.pdf

72 Baryonic Vortex and Topological Phases in Dense QCD

We study the low-energy QCD phase diagram under a magnetic field and at finite density. Both baryon chemical potential and isospin chemical potential are taken into account. The former is responsible for a domain wall configuration of the neutral pion, dubbed the chiral soliton lattice (CSL), with its origin from the chiral anomaly. The latter induces the charged pion condensate that can accommodate an Abrikosov vortex lattice (AVL). Either phenomenon requires a magnetic field above some critical value. Our findings show that an interplay between the two structures, which we call "CSL-AVL intersection", lowers the demanded critical magnetic field and therefore alters the phase diagram. Furthermore, a novel phase dubbed "Baryonic Vortex Lattice" is proposed, which conquers the AVL at higher baryon/isospin chemical potentials in the phase diagram. The result is phenomenologically relevant to neutron stars, particularly in regions with proton superconductors. The common mechanism applies to broader physical contexts that feature coexisting vortices and domain walls.

Speaker: Zebin Qiu

73 Baryon interactions in a pion superfluid at finite isospin chemical potential

Baryon interactions are one of the most fundamental quantities in nuclear physics. Their properties in vacuum have been extensively studied via scattering experiments and many theoretical methods. In medium, however, the baryon interactions are poorly examined, although they are indispensable to deepen our microscopic understanding on e.g. the structure of neutron stars and heavy-ion collision dynamics.

As a step toward the understanding of baryon interactions in medium, we analyze the baryon-baryon interactions at finite isospin chemical potential based on leading-order chiral Lagrangian. The Lagrangian possesses the isospin U(1) symmetry, spontaneously broken at the isospin larger than the pion mass. The resulting gapless phonon mediates the interaction between baryons. As in the case of polarons in superfluids [K. Fujii, M. Hongo, and T. Enss (2022)], the long-range part of the neutron-neutron interaction is described by a two-phonon exchange diagram and exhibits van der Waals-type scaling behavior. We will also discuss the baryon interactions including hyperons. Since the lattice QCD calculation can be performed at finite isospin chemical potential, this study provides a basis for reliably extending lattice QCD studies of baryon interactions to in-medium systems.

Speaker: Dr Asanosuke Jinno (KEK)

74 Meson Spectra in a Three-Flavor Quark–Meson Model at Finite Temperature and Isospin Density

We investigate meson properties in a three-flavor quark–meson (linear sigma) model at finite temperature and isospin chemical potential. The model incorporates explicit chiral symmetry breaking as well as the $U _A(1)$ anomaly via the Kobayashi–Maskawa–’t Hooft (KMT) interaction. Working in the mean-field approximation, we introduce both chiral condensates and a pion condensate to describe the possible emergence of a pion superfluid phase at large isospin density.

At tree level, we derive the meson mass spectra and analyze the mixing patterns among scalar and pseudoscalar modes, emphasizing the role of the anomaly term in splitting the flavor-singlet and octet channels. We then extend the analysis to one-loop order using the Matsubara formalism. The thermodynamic potential is constructed by including quark fluctuations, and the gap equations for the condensates are solved self-consistently.

We compute meson propagators and extract the in-medium spectra from the pole conditions, both in the normal phase and in the pion superfluid phase where meson mixing becomes nontrivial. The interplay between isospin density, chiral symmetry breaking, and the $U_A(1)$ anomaly is systematically explored. In particular, we discuss how the pion condensation modifies the meson spectrum and induces mixing between scalar and pseudoscalar channels.

Our results provide a unified framework to study meson properties at finite isospin density and may offer insights relevant to QCD phase structure and strongly interacting matter under extreme conditions.

Speaker: Yuhan Gao (Fudan University)

Registration & Opening: Closing

Convener: Seung-il Nam (Pukyong National University)