The 8th International Conference on Chirality, Vorticity and Magnetic Field in Quantum Matter

22 juil. 2024, 08:00 → 26 juil. 2024, 18:00 Europe/Bucharest

Amphitheater A11 (West University of Timisoara)

Victor Ambruș (West University of Timișoara, Romania), Maxim Chernodub (CNRS, Université de Tours, France)

The 8th International Conference on Chirality, Vorticity, and Magnetic Field in Quantum Matter will be held on July 22 - 26, 2024, at the West University of Timișoara, Romania. 

This event is the 8th conference in the series on Chirality, Vorticity, and Magnetic Field in Heavy-Ion Collisions, which has been extended in 2024 to include other domains of Quantum Matter. 

This one-week conference brings together researchers from different domains of physics, both from theoretical and experimental communities, to discuss new avenues in exploring chiral and vortical phenomena and associated electromagnetic effects in the fields of strongly interacting matter, heavy-ion collisions, superconductors, (magneto-)hydrodynamical systems and in astrophysical objects. 

Please note the Important Dates, Travel to Timișoara, and Visa Information.

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lundi 22 juillet

General: Start of registration

General: Welcome

Plenary: First day

test

Président de session: Francesco Becattini (Università di Firenze)

1 Polarization in relativistic nuclear collisions: Experiment

Review of the experimental status of the polarization measurements in heavy ion collisions is presented.

Orateur: Prof. Sergei Voloshin (Wayne State University)

2 Theoretical review on spin polarization

In this review talk, I discuss recent advancements in the theoretical understanding of polarization phenomena in heavy ion collisions. I will focus on recent theoretical developments concerning vector polarization and spin alignment, including their numerical study and comparison with experiments. I will highlight the successes and the open questions in the current models, offering insights into future research directions.

Orateur: Andrea Palermo (Stony Brook University)

10:30 Coffee break

Polarization: Session 1

Président de session: Radoslaw Ryblewski (Institute of Nuclear Physics PAN, Kraków, Poland)

3 Quark spin correlations in relativistic heavy ion collisions

The observation of the vector meson's global spin alignment by the STAR Collaboration reveals that strong spin correlations may exist for quarks and antiquarks in relativistic heavy-ion collisions in the normal direction of the reaction plane. We propose a systematic method to describe such correlations in the quark matter. The correlations can be classified as local and long range types. We show in particular that the effective quark spin correlations contain the genuine spin correlations originated directly from the dynamical process as well as those induced by averaging over other degrees of freedom. We also show that such correlations can be studied by measuring the vector meson's spin density matrix and hyperon-hyperon and hyperon-anti-hyperon spin correlations. We present the relationships between these measurable quantities and spin correlations of quarks and antiquarks.

Orateur: Qun Wang (University of Science and Technology of China)

4 Higher order terms in fermion spin polarization

In this talk I will present a derivation of second order terms
of the spin polarization of fermions at local thermodynamic equilibrium
including second order derivatives and quadratic terms in thermal
vorticity and shear. While quadratic terms are expected to provide
a small correction to the predicted polarization, the importance of
second order derivatives can be verified only through numerical
simulations.

Orateur: Francesco Becattini (Università di Firenze)

5 Pryce’s spin and polarization of massive Dirac fermions

A major difficulty in QFT comes from the fact that the traditional Pauli-Dirac spin operator of Dirac’s theory is not a conserved observable. This inconvenience can be overdrawn taking the Pauli-Lubanski operator as covariant spin operator, even though this is not related directly to an $SU(2)$ symmetry. Another possibility is to focus on the new spin and position operators proposed initially by Pryce long time ago and re-defined recently with the help of a new spin symmetry and suitable spectral representations. [I. I. Cot\u aescu, Eur. Phys. J. C (2022) 82:1073]. In this framework the quantization gives rise to a large set of one-particle operators with physical meaning, including the spin and orbital parts of isometry generators. A special attention is paid to the new spin and polarization one-particle operators which are compared with other operators describing polarization used so far.

Orateur: Ion Cotaescu (West University of Timisoara, Romania)

6 Spin Alignment Induced by Curvature of Freezeout Hypersurface

We derive a Cooper-Frye-type formula for the spin alignment of neutral vector mesons, such as $\phi$ mesons, at local thermal equilibrium. We describe the local equilibrium state with a grand canonical ensemble specified by temperature, fluid velocity, and spin potential. We develop a set of Feynman rules to evaluate the Wigner function order by order in space-time gradient.
We assume that the vector mesons freeze out on a space-like hypersurface in the Minkowski space-time that is close to a hyperplane. We find that the leading order of the spin alignment is proportional to the curvature of the hypersurface and the hydrodynamic fields at first-order space-time gradient, such as the thermal shear. It is a non-dissipative mechanism that induces the spin alignment proportional to the hydrodynamic fields with the first-order space-time gradient.

Orateur: Zhong-Hua Zhang (Fudan University)

13:00 Lunch break

Phase diagram: Session 1

Président de session: Prof. Kenji Fukushima (The University of Tokyo)

7 3D Pion crystal from the chiral anomaly

Including the effects of the chiral anomaly within Chiral Perturbation Theory at finite baryon chemical potential, it has been shown that neutral pions form an inhomogeneous phase dubbed the "Chiral Soliton Lattice" (CSL) above a certain critical magnetic field. Above a second (higher) critical field, the CSL becomes unstable to fluctuations of charged pions, implying they condense. I will point out the similarity of this second critical field to the upper critical magnetic field in conventional type-II superconductors, suggesting that an inhomogeneous superconducting charged pion phase exists beyond this point. Applying similar methods originally used by Abrikosov, I will present results where we've constructed such a phase, and show the region where it is preferred in the baryon chemical potential-magnetic field phase diagram at zero temperature. This new phase has a non-zero baryon number density which is periodic in all three spatial dimensions.

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

8 QCD phase diagram in the $T-eB$ plane for pion masses beyond its physical value

It is interesting to observe the effect of the pion mass beyond its physical value on the QCD phase diagram in the $T-eB$ plane. The fate of the inverse magnetic catalysis (IMC) and the behaviour of $T_{\rm CO}$ beyond the physical point are of particular interest. Lattice QCD studies hint at a possible elimination of IMC effects with increasing pion mass. We aim to understand the entire problem from an analytical perspective using effective models. We find that effective models can align with lattice results and are capable of capturing the underlying mathematical structure of the theory.

Orateur: Aminul Islam Chowdhury

9 Chiral Symmetry Breaking and Spin-One Condensates in Rotating Quark-Meson Systems

We explore chiral symmetry breaking in a rotating system within a quark-meson model of interacting massless quarks, incorporating tensor channels. Our findings reveal that new interaction channels emerge due to the explicit breaking of rotational symmetry due to non-zero rotation. We demonstrate that chiral symmetry breaking leads to the generation of two independent condensates: the conventional chiral condensate and a spin-one condensate. The chiral condensate results in a dynamical fermion mass, while the spin-one condensate is associated with the spin chemical potential. The quark-antiquark pairs with opposite spins possess a resultant spin moment, which can align with the net angular momentum, giving rise to a net spin moment for the ground state.

Orateur: Ashutosh Dash (Goethe Univeristy, Frankfurt)

16:00 Coffee break

Magnetic field and Rotation: Session 1

Président de session: Sushant Kumar Singh

10 Chiral Kinetic Theory in Curved Space Revisited and Radiative Corrections

It is usually believed that physics in off-equilibrium state can be equivalently studied using equilibrium state with suitable metric perturbation. We point out it is not the case for spin polarization phenomena: the exisiting chiral kinetic theory in curved space fails to recover all the couplings between spin and hydrodynamic gradients [1]. We present a new form of chiral kinetic theory in curved space, in which the equivalence is established [2]. The equivalence allows us to formulate spin polarization in hydrodynamic medium as a scattering problem, which is then studied using in-medium form factors [3,4]. We find radiative corrections to all couplings between spin and hydrodynamic gradients. Implications for local spin polarization of Lambda hyperon will be discussed.

[1] Y.-C. Liu, L.-L. Gao, K. Mameda and X.-G. Huang, Phys.Rev.D 99 (2019) 8, 085014
[2] J. Tian and S. Lin, to appear
[3] S. Lin and J. Tian, Acta Phys.Sin. 72 (2023) 7, 071201
[4] S. Lin and J. Tian, Eur.Phys.J.Plus 139 (2024) 2, 109

Orateur: Shu Lin (Sun Yat-sen University)

11 Baryon Stopping and Initial Angular Momoment in Heavy Ion Collisions

Non-central heavy-ion collisions contain large orbital angular momentum ($\sim 10^{3\sim 6} \hbar$) that, at high energies, is expected to induce strong vorticity in the hot bulk fluid and generate global spin polarization of produced particles. As the collision energy $\sqrt{s}$ approaches threshold, the observed global spin polarization should reach a maximum, then drop to zero as increased stopping competes with decreased initial momentum. Recent experimental measurements, however, appear to show a continual rise of hyperon polarization even down to $\sqrt{s} = 2.42$ GeV, suggesting a peak very near threshold and hard to interpret theoretically. Here, we develop a simple Glauber-based initial state model to investigate the initial distribution of angular momentum with respect to rapidity, and the dependence of this distribution on initial baryon stopping across a wide range of collisional beam energy. We estimate that the angular momentum per produced final particle at mid-rapidity peaks around 5 GeV, which presents a potential challenge to an interpretation of the spin polarization measurements near threshold as a consequence due to the initial angular momentum of the colliding system.

Orateur: Prof. Jinfeng Liao (Indiana University)

Flash talk and posters

12 Ideal-spin hydrodynamics on top of a rotating background

After formulating the angular momentum conservation in a covariant form, we consider the equations of spin hydrodynamics in the background of an uncharged fluid in global equilibrium with a non-vanishing thermal vorticity.
Assuming that the spin degrees of freedom are not in equilibrium, we derive relaxation-type equations for the components of the spin potential.
These equations generalize the existing literature on the spin waves which were derived on top of a fluid in a hydrostatic state, where the thermal vorticity is zero.
Our purpose is to understand the dynamics of relaxation of the spin potential to the thermal vorticity in a simple setup and also pave the way for realistic numerical simulations.

Orateur: Annamaria Chiarini (Goethe University)

13 Dirac Eigenvalue Distributions and the Chiral Magnetic Effect

We investigated the Dirac eigenvalue distributions at finite chiral chemical potential and strong magnetic field. We found that the eigenvalue distributions exhibit what is called the skin effect in condensed matter physics which is typical behavior when a topological transport is expected.

We also analyzed different distribution patterns by multiplying some matrices to the Dirac operator. The eigenvalues are placed not randomly but along lines only when the operator product corresponds to the physical observable relevant to the topological transport.

We also discuss possible applications of topological data analysis (TDA) to judge whether the topological current emerges.

Orateur: Prof. Kenji Fukushima (The University of Tokyo)

14 Helicity conservation for process of fermion production in Coulomb field on de Sitter universe

Fermion production in an external Coulomb field on de Sitter expanding universe is studied. The amplitude and probability of pair production in an external Coulomb field are computed and the cases of large/small values of the expansion factor comparatively with the particle mass are studied. We obtain from our calculations that the modulus of the momentum is no longer a conserved quantity. We find that in the de Sitter space there are probabilities for production processes where the helicity is no longer conserved.

Orateur: Cosmin Crucean (West University of Timisoara)

15 Shear viscosity of rotating, hot, and dense spin-half fermionic systems using Kubo formalism

In this study, we calculate the shear viscosity for rotating fermions with spin-half under conditions of high temperature and density. We employ the Kubo formalism, rooted in finite-temperature quantum field theory, to compute the field correlation functions essential for this evaluation. The one-loop diagram pertinent to shear viscosity is analyzed within the context of curved space, utilizing tetrad formalism as an effective approach in cylindrical coordinates. Our findings focus on extremely high angular velocities, ranging from 0.1 to 1 GeV, which align with experimental expectations. Furthermore, we explore the inter-relationship between the chemical potential and angular velocity within the scope of this study.

Orateur: Dr Rajeev Singh (Stony Brook University)

Shear viscosity of rotating, hot, and dense spin-half fermionic systems from quantum field theory

16 The advection-diffusion equation in the density frame

We investigate an alternative approach, to the MIS relativistic approach, developed to describe fluids without an underlying boost symmetry. This "density frame" approach has no non-hydrodynamic modes and no additional parameters compared to the Landau theory of first order hydrodynamics, at the price of not being fully boost invariant. We show that the density frame equations of motion follow Landau ones if the ideal equations are used to rewrite lab-frame time derivatives appearing in the dissipative strains as spatial derivatives. With this rewrite the equations are first order in time and are stable. In addition, we also show that the density frame equations can be derived from the relativistic kinetic theory.

Orateur: Dr Rajeev Singh (Stony Brook University)

The stochastic relativistic advection diffusion equation from the Metropolis algorithm

17 Dirac fermions under imaginary rotation

Recent years have seen an increase in the interest to investigate the thermodynamic properties of strongly-interacting systems under rotation. Such studies are usually performed using lattice gauge techniques on the Euclidean manifold and with an imaginary angular velocity, Ω = iΩ_I . When ν = βΩ_I /2π is a rational number, the thermodynamics of free scalar fields ”fractalizes” in the large volume limit, that is, it depends only on the denominator q of the irreducible fraction ν = p/q [1].

The present study considers the same problem for free, massless, fermions at finite temperature T = \beta^{-1} and chemical potential µ and confirms that the thermodynamics fractalizes when µ = 0. Curiously, fractalization has no effect on the chemical potential µ, which dominates the thermodynamics when q is large. The fractal behavior is shown analytically for the fermionic condensate, the charge currents and the energy-momentum tensor. For these observables, the limits on the rotation axis are validated by comparison to the results obtained in [2] for the case of real rotation. Enclosing the system in a fictitious cylinder of radius R and length Lz allows constructing averaged thermodynamic quantities that satisfy the Euler relation and fractalize.

[1] V. E. Ambruș, M. Chernodub, Phys. Rev. D 108 (2023) 085016.
[2] V. E. Ambruş, J. High Energ. Phys. 2020 (2020) 16.

Orateur: M. Tudor Pătuleanu (West University of Timisoara)

18 Acceleration as a circular motion along an imaginary circle

We describe a quantum fluid undergoing constant acceleration in the grand canonical ensemble, in thermal equilibrium at finite inverse temperature β. Writing the action of the density operator ρ as a Poincare transformation with imaginary parameters, we derive the Kubo-Martin-Schwinger (KMS) relation characterizing the two-point functions. The KMS relation sets boundary conditions for the Euclidean propagator, identifying points in the τ-z plane on a circle separated by an angle equal to the thermal acceleration α. When α/2π = p/q is a rational number, we find a fractalization of thermodynamics, similar to the case of states under imaginary rotation.

Orateur: Victor E. Ambruș (West University of Timișoara)

19 Helicity relaxation time in an interacting fermionic plasma

The polarization of free Dirac fermions can be described by helicity, which represents the projection of the spin along the direction of motion. The helicity operator commutes with the Hamiltonian and therefore helicity is a good'' quantum number, even in the case of massive fermions. This opens the possibility of defining ahelicity current'', J^\mu_H, which is conserved for free fermions. In the case of massless fermions, J^mu_H transforms covariantly under Lorentz transformations. Integrating its zeroth component over the spatial volume gives the helicity charge, Q_H.

Consider now an ensemble of interacting fermions with a slight helicity imbalance. Due to the helicity-violating pair annihilation (HVPA) processes, the helical imbalance will dissipate in time. This poster addresses the calculation of the typical timescale of the helicity relaxation time in the high-temperature, deconfined phase of the quark-gluon plasma, by employing the Boltzmann collision integral for the HVPA processes.

Orateur: Victor E. Ambruș (West University of Timișoara)

20 Helical effects in fermionic plasma

A quantum fluid in thermal equilibrium can be described in the grand canonical ensemble using the density operator ρ. At finite temperature and chemical potential, the expectation values of the energy-momentum tensor and the charge current reveal the well-known thermodynamics of the Fermi-Dirac fluid. When the system is rotating or immersed in a magnetic field, deviations from the Fermi-Dirac thermodynamics can be seen, a particular form of which gives rise to anomalous transport.

Anomalous transport was originally uncovered at the level of the axial current: a rotating fluid exhibits a flow of chirality along the rotation vector (the chiral vortical effect). Similarly, Dirac fermions in a magnetic field exhibit the chiral separation effect, by which vector charge imbalance drives a flow of chirality. Conversely, chiral imbalance drives a flow of vector charge (the chiral magnetic effect).

In this poster, we address similar effects at the level of the helicity current, describing the flow of helicity (as opposed to chirality) at finite rotation and in the presence of a magnetic field. Because the helicity has opposite charge conjugation parity compared to chirality, these transport laws complement each other. At high temperature and under rotation, the axial conductivity is dominant; while under a magnetic field, the helical conductivity becomes dominant.

Orateur: Victor E. Ambruș (West University of Timișoara)

21 Gluon matter under weak acceleration: lattice results

When two relativistic heavy nuclei collide, they produce strong chromoelectric fields that lead to a rapid deceleration of the colliding nuclei. It was suggested twenty years ago that the deceleration leads to a rapid thermalization of the gluon matter through the Hawking-Unruh effect that produces a final thermal gluon state via quantum tunneling through the emerging event horizon. In the Color Glass Condensate picture, the deceleration in the relativistic heavy-ion collisions has been estimated to reach an enormous value of $a \simeq 1$~ GeV. Around the same time, it was also demonstrated in a Nambu-Jona-Lasinio approach that the acceleration produces a phase transition to a chirally restored phase. In our work, we study the non-perturbative properties of gluon plasma subjected to weak acceleration using first-principle numerical Monte Carlo simulations. Under acceleration, the gluon plasma resides in local thermal equilibrium. We use the Luttinger (Tolman-Ehrenfest) correspondence between temperature gradient and gravitational field to impose acceleration in imaginary time formalism, which can be performed with the real-valued acceleration. We show that even the weakest acceleration of the order of $a \simeq 25$~MeV drastically softens the deconfinement phase transition, converting the first-order phase transition of a static system to a very soft crossover. On the other hand, we found that the weak acceleration of gluon plasma does not affect the critical temperature of the deconfinement transition.

Orateur: Dr Maxim Chernodub (CNRS, Université de Tours, France)

22 In- and out-of-equilibrium aspects of the Chiral Magnetic Effect from lattice QCD

In this work, we study the Chiral Magnetic Effect (CME) from lattice QCD simulations in two different scenarios, particularly focusing on the leading-order coefficient of the vector current in a chiral chemical potential expansion. In the first case, we consider a system in thermal equilibrium with a non-uniform magnetic background. We show that local chiral magnetic currents appear in this setup, following non-trivially the magnetic field profile. We check that these currents average zero in the full volume, confirming that the total CME conductivity vanishes in equilibrium. In the second case, we present the first steps towards studying the out-of-equilibrium aspects of CME on the lattice. We use Euclidean correlators, calculated in a uniform magnetic background, to investigate the out-of-equilibrium conductivity via spectral reconstruction methods.

Orateur: Eduardo Garnacho-Velasco (Bielefeld University)

mardi 23 juillet

Plenary: Second day

test

Président de session: Fuqiang Wang

23 Searches for Chiral Magnetic and Chiral Vortical Effects with ALICE

The interplay between the chiral anomaly and the magnetic/vortical field created in heavy-
ion collisions can give rise to anomalous chiral effects. In this talk, the latest results of the
Chiral Magnetic Effect, Chiral Magnetic Wave, and Chiral Vortical Effect are reported in
Pb–Pb and Xe–Xe collisions recorded by the ALICE detector.

Orateur: Alexandru Florin Dobrin (Institute of Space Science - INFLPR Subsidiary)

24 A Novel Approach to Search for CME from STAR and the Future Prospect

In this talk I will present the recent results of CME searches from the STAR collaboration using a novel event shape selection method and give a personal prospect on the future of the CME experimental searches. In high-energy heavy-ion collisions, the chiral magnetic effect (CME) may arise from the interplay between domains of chirality imbalanced quarks in the quark-gluon plasma and the strong magnetic field ($\vec{B}$) generated by spectator protons. The CME is predicted to induce an electric charge separation along the $\vec{B}$ direction, manifestly violating local $\cal{P}$ and $\cal{CP}$ symmetries. We use the  $\Delta\gamma^{112}$ correlator based on pairs of same- and opposite-sign charged hadrons to detect such a charge separation along the $\vec{B}$ direction. To remove the background induced by elliptic flow ($v_2$), we use a novel event shape selection (ESS) approach that classifies events based on their shapes which allows us to determine $\Delta\gamma^{112}_{\rm ESS}$ at the zero-$v_2$ limit. Furthermore, we use the spectator information to reconstruct the $\vec{B}$ direction, thereby minimizing nonflow backgrounds. We report the measurements of $\Delta\gamma^{112}$ and a background indicator $\Delta\gamma^{132}$ in Au+Au collisions from the RHIC Beam Energy Scan phase II and at the top RHIC energy. After background suppression, $\Delta\gamma^{132}_{\rm ESS}$ is consistent with zero, and $\Delta\gamma^{112}_{\rm ESS}$ is reduced from inclusive $\Delta\gamma^{112}$ by more than five-fold. The measured $\Delta\gamma^{112}_{\rm ESS}$ value in the 20\%--50\% centrality range is finite with an over $3\sigma$ significance at each of center-of-mass energies 11.5, 14.6, and 19.6 GeV, whereas the corresponding values at other beam energies are consistent with zero within uncertainties. The STAR results present intriguing scenarios for the RHIC BES regime and more theoretical insights are needed. I will comment on future prospect related to experimental CME searches.

Orateur: Huan Huang (UCLA)

10:30 Coffee break

Chiral Magnetic Effect: Session 1

Président de session: Di-Lun Yang (Institute of Physics, Academia Sinica)

25 Search for the Chiral Magnetic Effect by Event Shape Engineering Differentially in Invariant Mass in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV from STAR

Chiral Magnetic Effect (CME) is a phenomenon in which electric charge is separated by a strong magnetic field from local domains of chirality imbalance and parity violation in quantum chromodynamics (QCD). The CME-sensitive observable, charge-dependent three-particle azimuthal correlator $\Delta\gamma$, is contaminated by a major physics background proportional to the particle elliptic anisotropy ($v_{2}$). In this talk, we report a new analysis from STAR on charge separation using the Event Shape Engineering (ESE) approach [1], projecting $\Delta\gamma$ to zero $v_{2}$ to obtain the intercept $\Delta\gamma_{ESE}$ in which flow-driven background is largely suppressed. Our approach has several novel aspects: (1) we use three subevents to select dynamical fluctuations of $v_{2}$ by separating particles of interest from ESE selection; (2) we apply the ESE method differentially as a function of the pair invariant mass of particles of interest since CME is a low-$p_{T}$ phenomenon and hence more sensitive to lower mass; (3) we investigate remaining nonflow contamination in the extracted intercept [2]. We report preliminary results in Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV from STAR using the event plane reconstructed with the time projection chamber (TPC) and the spectator plane reconstructed with the zero-degree calorimeter (ZDC). We compare our results to Anomalous-Viscous Fluid Dynamics (AVFD) model simulations [3].

Orateur: M. Han-Sheng Li (Purdue University)

26 The effect of electric and chiral magnetic conductivities on azimuthally fluctuating electromagnetic fields and observables in isobar collisions

We study the space-time evolution of electromagnetic fields along
with the azimuthal fluctuations of these fields and their correlation
with the initial matter geometry specified by the participant plane
in the presence of finite electric $\left(\sigma\right)$ and chiral
magnetic $\left(\sigma_{\chi}\right)$ conductivities in Ru+Ru and
Zr+Zr collisions at $\sqrt{s_{NN}}=200$ GeV. We observe the partially
asymmetric behavior of the spatial distributions of the electric and
magnetic fields in a conducting medium when compared to the Lienard-Wiechert
(L-W) solutions, and deceleration of the decay of the fields is observed
in both isobar collisions. While studying the correlation between
the magnetic field direction and the participant plane, we see the
sizeable suppression of the correlation in the presence of finite
conductivities when compared to the L-W case, reflecting the importance
of taking into account the medium properties such as conductivities
while calculating the magnetic field induced observable quantities.

Orateur: Irfan Siddique (University of Chinese Academy of Sciences)

27 Negative magnetoresistence in Dirac Semimetals from Keldysh technique

Negative magnetoresistance in topological semimetals is typically considered as a manifestation of chiral magnetic effect (CME). The relation between these two phenomena has the status of hypothesis and is based on the sequence of assumptions. In the present paper we rely on rigorous Keldysh technique of non-equilibrium theory. It allows us to investigate the accumulation of axial charge — the process that involves both chiral anomaly and relaxation followed by the energy dissipation.
We also calculate directly the contribution to electric conductivity due to the same two processes. We obtain the same dependence of conductivity on the angle between electric and magnetic field as the standard heuristic CME calculation. The dependence of conductivity on magnetic field in the limit of weak magnetic field also matches the CME calculation. However, comparison of axial charge density and electric conductivity does not confirm the CME hypothesis, and demonstrates that the true mechanism of magnetoresistance in Dirac semimetals is (partially or completely) different from the one based on the CME.

Orateur: Ruslan Abramchuk (Ariel University, Israel)

28 Spacetime dynamics of chiral magnetic currents in a hot non-Abelian plasma

The correlations of electric currents in hot non-Abelian plasma are responsible for the experimental manifestations of the chiral magnetic effect in heavy-ion collisions. We evaluate these correlations using holography, and show that they are driven by large-scale topological fluctuations. In a non-Abelian plasma with chiral fermions, local axial charge can be generated either by topological fluctuations (creating domains with nonzero Chern-Simons number) or by thermal fluctuations. Within holography, we investigate the dynamical creation of the axial charge and isolate the imprint of the topological dynamics on the spatial correlations of electric current. In particular, we show that the spatial extent of the current correlation is quite large (∼1  fm) and grows with time, which is consistent with sphaleronlike dynamics. We provide numerical estimates for this spatial size that can be used as an input in phenomenological analyses.

Orateur: Sebastian Grieninger (Stony Brook University)

13:00 Lunch break

Chiral Magnetic Effect: Session 2

Président de session: Sebastian Grieninger (Stony Brook University)

29 Chiral transport phenomena in core-collapse supernovae

The dynamics of relativistic leptons such as electrons and neutrinos play an important role in the evolution of core-collapse supernovae (CCSN). Nevertheless, chirality as one of the fundamental microscopic properties that could affect lepton transport through the weak interaction has been widely overlooked. In this talk, I will discuss how chiral effects such as the (effective) chiral magnetic effect (CME) for an electric charge current induced by magnetic fields could result in unstable modes of magnetic fields and inverse cascade, which may further influence the matter evolution in CCSN, pulsar kicks, and dynamical generation of strong magnetic fields in magnetars. I will also show how such an effective CME could be realized via the backreaction from non-equilibrium neutrino radiation even in the absence of chiral imbalance.

Orateur: Di-Lun Yang (Institute of Physics, Academia Sinica)

30 Chiral Magnetic and Vortical Effect in the Chiral Kinetic Approach using AMPT model

Built upon the state-of-the-art model a multiphase transport (AMPT), we develop a new module of chiral anomaly transport (CAT) to trace the evolution of the initial topological charge of gauge field created through sphaleron transition at finite temperature and external magnetic field in heavy ion collisions. The eventual experimental signals of chiral magnetic effect(CME) has been measured. The CAT explicitly shows the generation and evolution of the charge separation, and the signals of CME through the CAT are quantitatively in agreement with the experimental measurements in Au+Au collision and isobar collision at $\sqrt{s}=200 {\rm GeV}$, and the centrality dependence of the CME fraction .

Orateur: Zilin yuan (中国科学院大学核科学与技术学院)

31 Conductivities of CME, CSE and QHE as topological invariants

We recent results of our group on quantum Hall effect, Chiral Magnetic effect, and Chiral separation effect. Using Wigner - Weyl calculus the corresponding conductivities are calculated and represented in the form of topological invariants. Effects of interactions, inhomogeneity, and deviations from equilibrium are considered.

Orateur: Prof. Mikhail Zubkov (Ariel University, Israel)

16:00 Coffee break

Hydrodynamics: Session 1

Président de session: Matthias Kaminski (University of Alabama, U.S.A.)

32 Latest updates on ideal-spin hydrodynamics

Spin hydrodynamics can be developed from a systematic expansion in the reduced plank constant. Up to the first order in this expansion, there is no back-reaction from the spin to fluid dynamics, and, therefore, solutions to the standard hydrodynamics act as an input for the equations of motion for the spin tensor. Furthermore, one can assume a so-called ideal-spin approximation where the entropy production from the spin degrees of freedom is second-order in the reduced plank constant and the conservation of angular momentum is a closed system of equations. In this talk, I present developments in ideal-spin hydrodynamics including the linear regime, the covariance of spin dynamics, and the spin dynamics on top of Bjorken attractors.

Orateur: Masoud Shokri (Goethe University)

33 Relativistic Quantum-statistical formulation of spin hydrodynamics

Motivated by the evidence of spin polarization of particles produced in relativistic heavy ion collisions, there is a growing interest in the so-called relativistic spin hydrodynamics. In this talk, we will present the outcomes of using a first-principle quantum-statistical method to derive the expression of the entropy current and entropy production rate in relativistic spin hydrodynamics. We'll discuss key findings in comparison to phenomenological spin hydrodynamics, along with its future potential.

Ref: [Phys.Lett.B 850 (2024) 138533]

Orateur: Asaad Daher (IFJ PAN Krakow Poland)

34 Dynamical generation of canonical spin potential in hot QCD

Spin hydrodynamics relies on the non-unique definition of the spin tensor, representing the distribution of spin degrees of freedom, but different spin tensors lead to different physical results. In general, this pseudogauge symmetry represents a significant theoretical ambiguity in relativistic out-of-equilibrium statistical mechanics. This ambiguity may be resolved by fundamental quantum field theory. In this talk, we prove the equivalence between the finite-temperature NJL model and the covariant statistical operator of a free Dirac field with a spin potential coupled to the canonical spin tensor. The spin potential is induced by a mean axial vector field, expected to be generated in heavy-ion collisions through the chiral separation and axial vortical effects. Our description favors the canonical pseudogauge.

Orateur: Matteo Buzzegoli (West University of Timisoara)

18:00 Boat trip

mercredi 24 juillet

Phase diagram: Session 2

Président de session: Ashutosh Dash (Goethe Univeristy, Frankfurt)

35 Mixed inhomogeneous phase in vortical gluon plasma from lattice simulation

Using first-principle numerical simulations, we find a new spatially inhomogeneous phase in rigidly rotating gluon plasma. This mixed phase simultaneously possesses both confining and deconfining phases in thermal equilibrium. Unexpectedly, the local critical temperature of the phase transition at the rotation axis does not depend on the angular frequency within a few percent accuracy. An analytic continuation of our results to the domain of real angular frequencies indicates a profound breaking of the Tolman-Ehrenfest law in the vicinity of the phase transition, with the confining (deconfining) phase appearing far (near) the rotation axis.

Orateur: Artem Roenko (JINR)

36 Chiral symmetry breaking and restoration for an accelerated and rotated observer

In the relativistic heavy ion collision experiment, there exist a large acceleration and rapid rotation in the non-central collision which can be considered as a system with acceleration and rotation. According to the Hawking-Unruh effect, the accelerated observer sees himself in a system with Unruh temperature $T/2\pi$. And the color glass condensate picture predicts that in heavy ion collision the particle under a strong color-electric field with strength $E\sim Q^2_s/g$ ($Q_S$ is the saturation scale, and g is the strong coupling) which will provide a typical acceleration $a \sim Q_s \sim 1 GeV$ such that the Unruh temperature $T\sim 200 MeV$ which is large than the pseudo-critical temperature for QCD phase transition. It means that the Unruh effect may play an important role in QCD phase transition. The chiral symmetry breaking and restore for an accelerating observer have been discuss in the past study. As the QGP is the most vortical fluid, QCD matter under rotation has attracted many attentions. In this work we study the chiral symmetry for an observer under both acceleration and rotation.
We study the chiral condensate as observed by an accelerating and rotating observer using field theory in general spacetime. We develop the formalism to calculate the chiral condensate using the Nambu-Jona-Lasinio model in accelerating and rotating frame. We solve the gap equation and obtain the chiral condensate as a function of proper acceleration and angular velocity. We also defined a critical acceleration $a_c$ where the chiral symmetry restore. As one of our main results, $a_c$ as a function of rotation angular velocity $\omega$ was obtained. And we also study the constituent quark mass and neutral pion condensate in the case with the presence of ${a}\cdot {\omega}$. Like the case in parallel electromagnetic field, we observe a chiral rotation form the $\sigma$-direction toward the $\pi$-direction.

Orateur: Zhibin Zhu (Fudan university)

37 Inhibition of splitting of confining and chiral transition by rotation.

We will discuss the effect of rotation on the confining and chiral properties of QCD using the linear sigma model coupled to the Polyakov loop. Enforcing the causality constraint by the spectral boundary conditions we obtain the phase diagram at finite temperature, baryon density, and angular frequency. At nonrotating limit we observe a splitting between the chiral and confining transitions that decreases with increasing radius. In the presence of finite rotation this splitting decreases with increasing angular velocity for experimentally relevant, slow angular velocities. However, we observe a increment in the splitting when the boundary of the system rotates at near-to-light velocities.

Orateur: pracheta singha (West University of Timisoara)

10:30 Coffee break

Hyperons: Session 1

Président de session: Andrea Palermo (Stony Brook University)

38 Measurement of global and local spin polarization of $\Lambda$ and $\bar{\Lambda}$ in Au+Au collisions from the RHIC Beam Energy Scan-II

Significant global hyperon polarization has been observed in non-central heavy ion collisions, providing evidence of the vorticity of the quark-gluon plasma (QGP). This effect can serve as a new probe for exploring the fluid properties of strongly interacting matter. A difference between the global polarization of $\bar{\Lambda}$ and $\Lambda$ could originate from the strong late-stage magnetic field in heavy ion collisions. In addition, local vorticity in the transverse plane, related to collective flow and density fluctuations, can lead to polarization along the beam direction, known as local polarization. A baryonic spin Hall effect is also predicted, with local polarization difference of $\Lambda$ and $\bar{\Lambda}$ induced by the gradient of the baryonic chemical potential.

In this talk, we will present new results of $\Lambda$ and $\bar{\Lambda}$ global polarization in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 9.2, 11.5, 14.6 and 17.3 GeV from RHIC BES-II with upgraded STAR detector systems. We also present results of local polarization for $\Lambda$ and $\bar{\Lambda}$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 27 GeV from BES-II. Our measurements can provide important insights into the late-stage magnetic field sustained by the QGP and the spin Hall currents possibly created in a highly dense baryonic environment.

Orateur: Tong Fu

39 Hyperon polarization along the beam direction in pPb collision at CMS

The observation of hyperon polarization along beam direction ($P_z$) in nucleus-nucleus collisions has opened a new way to study the complex vortical structures of the QGP. With the high-statistics data collected by the CMS experiment, we present the first $P_z$ results for $\Lambda$ and $\bar{\Lambda}$ particles in pPb collision at $\sqrt{s_{NN}}= 8.16$ TeV over a wide transverse momentum and multiplicity range. The measured $P_z$ signal can shed light on the origin of collectivity in small collision systems as well as the mechanism of spin polarization in heavy ion collisions.

Orateur: Chenyan Li (Shandong University)

40 Global Hypertriton Polarization in Au+Au collisions at $\sqrt{s_{NN}}=7.7-200$ GeV

Particles of non-zero spin produced in non-central heavy-ion collisions are expected to be polarized along the direction perpendicular to the reaction plane due to spin-orbit coupling in the produced matter, and this has indeed been observed for many hyperons and vector mesons. Here, we show that the hypertriton ($_\Lambda^3$H), which is the lightest hypernucleus, is also polarized in these collisions. Using the coalescence model based on the kinetic freezeout baryons for light (hyper-)nuclei production, we find that the angular distribution of the decay product of polarized  $_\Lambda^3$H is highly sensitive to the spin configuration of its wavefunction, providing a novel way to determine its spin structure. We also predict the beam energy dependence of $_\Lambda^3$H  polarizations in heavy-ion collisions from a few to hundreds GeV based on a multi-phase transport model (AMPT) and coalescence model. We further discuss the comparation of the global polarization between hypertriton and hyperon with the energy dependence. These patterns of the global $_\Lambda^3$H polarization are expected to be tested in future experiments.

Orateur: Dai-Neng Liu

41 Lambda-(anti)Lambda Spin Correlation in Heavy-Ion Collisions

Recent experimental data indicate a strong phi vector meson spin alignment which can be explained as a result of a short distance correlation of fluctuating strong-force field. If such strong-force for strange quark exists in the late stage of heavy-ion collisions, it will also lead to spin-spin correlation of final state hyperons such as Lambda-(anti)Lambda. We calculate such spin-spin correlation within the CLVisc hydrodynamics with the strength of the fluctuating strong-field given by the phi meson spin alignment. The correlation is found to be 100 times stronger than that due to spin polarization by local vorticity.

Orateur: Xin-Nian Wang (Central China Normal University)

13:00 Lunch break

Plenary: Third day

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Président de session: Victor E. Ambruș (West University of Timișoara)

42 Phase diagram under rotation and magnetic field

I will review the recent discussions on the phase diagram under rotation and magnetic field. The interpretation of rotation effects on the QCD phase transition is still controversial, and the coexisting of rotation and magnetic field makes the physical system even more confusing. The talk will go through results from lattice results, model calculations, perturbative QCD, as well as the latest surprise from general analysis.

Orateur: Prof. Kenji Fukushima (The University of Tokyo)

43 CME-2024

A review talk on some of the new developments on the Chiral Magnetic Effect.

Orateur: Dmitri Kharzeev (Stony Brook University and BNL)

16:00 Coffee break

Polarization: Session 2

Président de session: Sergei Voloshin (Wayne State University)

44 Vortical waves in a fluid with massless fermions

The anomalous axial symmetry of the Lagrangian for massless fermions is known to be ultimately responsible for a variety of macroscopic transport phenomena in rotating states, e.g. the chiral vortical effect (CVE) and chiral vortical separation effect (CVSE). Their coherent interplay gives rise to the chiral vortical wave. Traditionally, only the axial and vector degrees of freedom are included in the hydrodynamic analysis. In this talk, we generalise the previous approaches to include another conserved charge for massless free fermions, helicity, and obtain the spectrum of collective excitations. We explicitly introduce the dissipative effects and non-conservation of charges that arise due to interactions. Finally, we discuss the possible phenomenological impact for the quark-gluon plasma nucleated in heavy-ion collisions.

Orateur: Sergio Morales Tejera (West university of Timisoara)

45 Measuring the Global Spin Alignment of ϕ meson in Heavy Ion Collisions by STAR

In non-central heavy-ion collisions, a large orbital angular momentum is produced. A part of the orbital angular momentum can polarize the quarks and anti-quarks, hence the vector mesons, inside the medium. Recently, STAR measured the global spin alignment of ϕ(1020) and K∗ (892) mesons in Au+Au collisions from the RHIC Beam Energy Scan I (BES I) program [1]. The global spin alignment, quantified by the 00th coefficient of the spin density matrix, ρ00, is measured by a fit to the acceptance and efficiency corrected ϕ meson yield versus polar angle (θ∗) between the daughter kaon in the parent’s rest frame and the orbital angular momentum direction. In this talk, we present an alternative approach to extract ρ00 by utilizing the ⟨cos2θ∗⟩ as a function of pair-invariant mass instead of analyzing the ϕ meson yields in cos θ∗ bins. We use a data-driven method to correct for acceptance and efficiency. We report new analysis from this method.

[1] M. Abdallah et al. (STAR Collaboration), Nature 614, 244–248 (2022).

Orateur: CW Robertson (Purdue University)

46 Spin alignment of vector mesons in holographic model

The global spin alignment for the $\phi$ meson has been recently observed by the STAR collaboration at RHIC, implying that the spin of its consituent quark has a significant correlation with the spin of the consituent antiquark, which may arise from their strong interaction with the quark-gluon plasma. We develop a general framework for studying the spin alignment $\rho_{00}$ for flavorless vector mesons by using the gauge/gravity duality. Focusing on the dilepton production through vector meson decay, we derive the relation between production rates at each spin channel and meson’s spectral function, which can be evaluated by holographic models for a strongly coupled system. As examples, we study $\rho_{00}$ for $J/\psi$ and $\phi$ mesons, induced by the relative motion to a thermal background, within the soft-wall model. We show that $\rho_{00}$ in the helicity frame for $J/\psi$ and $\phi$ mesons have positive and negative deviations from 1/3 at $T=150$ MeV, respectively, which consequently leads to different properties for their global spin alignments.

Orateur: Xin-Li Sheng (INFN Firenze)

jeudi 25 juillet

Plenary: Fourth day

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Président de session: Maxim Chernodub

47 The Chiral Magnetic Effect and Chiral Separation Effect from the lattice QCD perspective

In this talk, I will review how the conductivities of anomalous transport phenomena can be extracted using lattice QCD, in particular focusing on the Chiral Separation Effect (CSE) and Chiral Magnetic Effect (CME). For the CSE, I will explain how the sign problem has been circumvented to study this effect in different setups, leading to the determination of its conductivity in QCD with physical quark masses. In the case of CME, I will emphasize the role of regularization for its equilibrium formulation, as well as the importance of using conserved vector currents on the lattice to study this effect. Finally, I will discuss what are the next steps being taken in the lattice community to shed light on how CME manifests in physical systems.

Orateur: Eduardo Garnacho-Velasco (Bielefeld University)

48 Lattice study of rotating QCD properties

In this report the influence of relativistic rotation on QCD properties will be considered. I am going to review the results which were obtained within lattice simulation of QCD. It has become commonplace to perform such studies in the reference frame rotating with the system under investigation. In this case there appears the gravitational field and the problem is reduced to study of QCD in this external gravitational field. Within the report the following topics will be reviewed. The influence of relativistic rotation to the QCD critical temperatures. Equation of state of rotating QCD and the moment of inertia of quark-gluon plasma. Inhomogeneous phase transitions in rotating quark-gluon plasma.

Orateur: Victor Braguta (JINR)

10:30 Coffee break

Magnetic field and Rotation: Session 2

Président de session: Igor Shovkovy (Arizona State University)

49 Gauge invariance and thermodynamic stability of rotating magnetized systems

In this presentation, I revisit the Dirac theory under an external magnetic field and rotation. Motivated by experimental observations of significant vorticities in heavy ion collisions, there has been active exploration into the thermodynamics of rotating QCD matter. While the pure rotational effect has received attention, the interplay between rotation and magnetic fields remains insufficiently elucidated. In this talk, I address two significant issues present in previous formulations of rotating magnetized systems: gauge invariance and thermodynamic stability. I demonstrate that resolving both issues necessitates considering the kinetic angular momentum coupled with angular momentum. The reformulated Dirac theory presented here reproduces a well-known charged density first discovered by Hattori and Yin. Moreover, it indicates that higher-order contributions of angular velocity do not affect the charge density, providing evidence of its anomalous nature. Lastly, I offer insights into the rotational response of QCD vacuum from the perspective of the Savvidy vacuum.

Orateur: Kazuya Mameda (Tokyo University of Science)

50 Effective Lagrangian for the macroscopic motion of fermionic matter

We consider macroscopic motion of quantum field systems. The Zubarev statistical operator allows us to describe several types of motion of such systems in thermal equilibrium. We formulate the corresponding effective theory on the language of a functional integral. The effective Lagrangian is calculated explicitly for the fermionic systems interacting with dynamical gauge fields. Possible applications to physics of quark-gluon plasma are discussed.

Orateur: Maik Selch (Ariel University, Israel)

51 Influence of magnetic field-induced anisotropic gluon pressure during pre-equilibrium

Magnetic fields of a large intensity can be generated in peripheral high-energy heavy-ion collisions. Although the intensity drops down fast and, moreover, it is not clear whether the fields last long enough to induce a magnetization during the quark-gluon plasma phase, most of the models and simulations predict a significant intensity that lasts up to proper times of order 1 fm after the beginning of the reaction, which is a typical time for the hydrodynamical phase to start. This interval of time is referred to as the pre-equilibrium stage. One can expect that the evolution of the reaction during pre-equilibrium is likely to be influenced by these fields. In this work we adopt a strong field approximation to study the effects of the magnetic field-induced anisotropy in the gluon pressure. We include this anisotropy within the description obtained by means of effective kinetic theory and explore the consequences to reach isotropization at proper times of order 1 fm.

Orateur: Ana Mizher (IFT-UNESP)

52 Magnetic catalysis and diamagnetism from pion fluctuations

In the framework of Nambu--Jona-Lasinio model beyond mean field approximation, the effects of pion fluctuations on (inverse) magnetic catalysis and magnetic susceptibility are studied. The negative magnetic susceptibility at low temperature is observed when contributions from both neutral and charged pions are taken into account. In weak field approximation, it is observed that at finite temperature, the magnetic inhibition effect in the chiral limit, resulting from the difference between the transverse and longitudinal velocities of neutral pions, converts to weak magnetic catalysis when considering a non-zero current quark mass. Moreover, the magnetic catalysis is amplified by the charged pions.

Orateur: Jie Mei (中国科学院大学物理科学学院)

13:00 Lunch break

Hydrodynamics: Session 2

Président de session: Sergio Morales Tejera (West university of Timisoara)

53 Chirality and a strong magnetic field give rise to novel hydrodynamic transport near and far from equilibrium

When chiral charged matter is exposed to extremely strong magnetic fields, novel hydrodynamic transport effects emerge 1. These novel effects need to be estimated and possibly taken into account, for example in the hydrodynamic codes used to analyze heavy-ion collision data or magnetars. Kubo formulae link the macroscopic transport coefficients to the microscopic retarded two-point correlation functions of conserved currents. Some among the transport effects cause no dissipation, i.e. they produce no entropy; one well known example is the chiral magnetic effect (CME). As a case study far away from equilibrium, the CME within holographic plasma suggests lessons for the quark-gluon-plasma at colliders 2.
References: Phys.Rev.C 105 (2022) 3, 034903; JHEP 04 (2021) 078

Orateur: Matthias Kaminski (University of Alabama, U.S.A.)

54 Pinched singularity and long time tail

Hydrodynamic nonlinearity manifests itself as long time tail in the hydrodynamic correlation functions. This corresponds to the singularity of the correlation function in momentum space. We argue that the latter is actually a "pinched singularity" of the integrand in the integral associated with a bubble diagram. We then address how to find the pinched singularity by solving the "Landau Loop Equations" and thus find the long time tail. Finally, by using this approach we read the long time tails of the shear stress tensor correlation functions in two theories: relativistic hydrodynamics and (chiral) magnetohydrodynamics.

Orateur: Navid Abbasi

55 Relaxation terms for anomalous hydrodynamic transport in Weyl semimetals

Weyl semimetals, a class of topological materials, exhibit a hydrodynamic regime and offer an ideal environment for investigating chiral anomalies through table-top experiments and transport measurements. In this presentation, I will consider a $(3+1)$-dimensional fluid with a $U(1)_V \times U(1)_A$ chiral anomaly as a model of Weyl semimetals. My focus will be on longitudinal thermoelectric magnetotransport, where I will search for relaxation models that meet fundamental and phenomenological constraints, including electric charge conservation, Onsager reciprocity, and finite DC conductivities. I will take into account all possible mixed energy, electric, and axial charge relaxations and show how models which respect these constraints unavoidably render the system open, thus violating the second law of thermodynamics. Furthermore, these relaxations lead to a novel prediction for the DC thermoelectric transport, opening the path to experimental verification. To conclude, I will discuss how mixed relaxations arise naturally from kinetic theory using a modified relaxation time approximation.

Orateur: Luca Martinoia (University of Genova)

16:00 Coffee break

Magnetic field and Rotation: Session 3

Président de session: Ana Mizher (IFT-UNESP)

56 Charge transport in strongly magnetized relativistic matter

Using the imaginary part of the self-energy function in the Landau-level representation, we derive the fermion damping rate in a hot magnetized plasma at the leading order of coupling. The results are used to investigate the longitudinal and transverse electrical conductivities. In the relativistic regime, these conductivities exhibit a scaling behavior expressed in terms of dimensionless functions of eB/T², where T represents the temperature and B the magnetic field. We demonstrate that the underlying mechanisms governing the transverse and longitudinal conductivities differ significantly, resulting in a substantial suppression of the former compared to the latter. We also extend our analysis to a magnetized quark-gluon plasma, although the approximation has limited validity at strong coupling.

Orateur: Prof. Igor Shovkovy (Arizona State University)

57 Electromagnetic field induction in quark-gluon plasma due to thermoelectric effects

Quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions cools rapidly as the medium evolves. QGP with non-zero conserved charged current, higher thermal conductivity of medium advances in global thermalization. Being made of electrically charged partons, heat current leads to electromagnetic (EM) field induction in the medium, commonly known as the thermoelectric effect. Quantum modification of the classical non-relativistic phenomenon in relativistic matter – QGP, is fascinating to explore. In this work, for the first time, we have estimated the induced electric field due to the thermoelectric effects in a QGP. This phenomenon can induce an EM field even in QGP created in head-on collisions with non-vanishing chemical potential. We found that the induced electric field is zero at the center and increases moving away from the center. For baryon chemical potential of $0.3$ GeV, the maximum induced field could be as high as $1~m_π^2$.

Orateur: Jayanta Dey (IIT Indore)

58 The weak magnetic effect on the direct photon production and hyperon local spin polarization

It is expected that there exists an ultra-central strong magnetic field during the early stages of heavy-ion collisions. However, due to the rapid decay, it is a weak magnetic field that along with the evolution of quark-gluon plasma (QGP)

In this work, we study the dissipative correction induced by a weak magnetic field during the QGP stage. Employing the viscous hydrodynamics simulation, we calculate two associated probes with weak magnetic dissipation, i.e., the direct photon elliptic flow and the hyperon local spin polarization.

We find that the magnetic field can lead to a large enhancement of the photon momentum anisotropy when coupled with the longitudinal dynamics of the background medium. With a finite magnetic field, the experimental measured direct photon $v_2$ can be well reproduced but with less than a 10% increment on the photon yield. On the other hand, we find that the weak magnetic correction on the quark phase distribution has a significant contribution to the local spin polarization and even flips the sign. The spin cooper frye formula with the weak magnetic correction is obtained. After incorporating this novel effect, one can reproduce the second and third modulation of local spin polarization along the beam direction, not only the sign but also the centrality dependence. Finally, the required magnetic field for these two observables is about 0.1 $m_{\pi}^2$.

arxiv:2302.07696
Phys.Rev.C 109 (2024) 3, 034917
arxiv:2401.07458

Orateur: Jing-An Sun (Mcgill and Fudan University)

19:00 Social dinner

vendredi 26 juillet

Plenary: Fifth day

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Président de session: Matteo Buzzegoli (West University of Timisoara)

59 Transport properties from quantum kinetic theory

Quantum kinetic theory, arising as a semiclassical limit of quantum field theory, is an effective microscopic description applicable to a wide variety of systems.
I present an introduction to the topic and discuss important developments, such as the application of quantum kinetic theory to systems of particles with nonvanishing spin, leading to intriguing transport phenomena relevant to the study of the Quark-Gluon Plasma (QGP).
In particular, emphasis is put on the connection of a quantum-kinetic approach to polarization-related phenomena in heavy-ion collisions.

Orateur: David Wagner

10:30 Coffee break

Polarization: Session 3

Président de session: Xin-Li Sheng (INFN Firenze)

60 Chiral restoration driven spin polarization

Semiclassical expansion of the Wigner function for spin-1/2 fermions having an effective spacetime-dependent mass is used to analyze spin-polarization effects. The existing framework is reformulated to obtain a differential equation directly connecting the particle spin tensor with the effective mass. It reflects the conservation of the total angular momentum in a system. In general, we find that the gradients of mass act as a source of the spin polarization. Although this effect is absent for simple boost-invariant dynamics, an extension to non-boost-invariant systems displays a non-trivial dependence of the spin density on the mass indicating that the spin polarization effects may be intertwined with the phenomenon of chiral restoration.

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Reference: Physics Letters B 849 (2024) 138464 • e-Print: 2307.12436 [hep-ph]

Orateur: Radoslaw Ryblewski (Institute of Nuclear Physics PAN, Kraków, Poland)

61 Spin 1 mesons as a probe for vorticity-polarization non-equilibrium

It is now clear, on a theoretical level, that spin polarization can not be in perfect local equilibrium with vorticity during the quark-gluon plasma evolution. Phenomenological consequences of this are however so far not clear. In this talk we argue that spin one mesons (and higher spin particles) are ideal probes of non-equilibrium between vorticity and polarization, because their density matrix carries, potentially, information unanbiguously related to local equilibrium.
We illustrate how light mesons (modeled via coalescence), quarkonia (modeled via potential models) and virtual photons (detectable via dilepton pairs) could be used to probe the interplay between vorticity and polarization in the system.
Based on 2305.02985 2104.12941 and ongoing work

Orateur: Giorgio Torrieri (University of Campinas)

62 Effect of the QCD critical point on spin polarization of $\Lambda$ hyperons

We investigate the effects of the QCD critical point on spin polarization of $\Lambda$ hyperons. For this we evaluate thermal vorticity and thermal shear by solving the equations of relativistic causal hydrodynamics in (3+1) dimensions. The effects of the critical point are incorporated through the equation of state and the scaling behaviour of the transport coefficients. For the same global polarization, we find a significant suppression in the rapidity profile of the component of polarization along the angular momentum direction due to the critical point. The study suggests that the change induced by the critical point in the rapidity dependence of the spin polarization of $\Lambda$ hyperons can be used as an indicator of the critical point.

Reference:
[1] Sushant K Singh & J Alam, Eur. Phys. J. C 83, 585 (2023).

Orateur: Sushant Kumar Singh

63 Longitudinal spin polarization in a thermal model with dissipative effects

In this work, we address the problem of longitudinal spin polarization of the $\Lambda$ hyperons produced in relativistic heavy-ion collisions. We combine a relativistic kinetic-theory framework that includes spin degrees of freedom treated in a classical way with the freeze-out parametrization used in previous investigations. The use of the kinetic theory allows us to incorporate dissipative corrections (due to the thermal shear and gradients of thermal vorticity) into the Pauli-Lubanski vector that determines spin polarization and can be directly compared with the experimental data. As in earlier similar studies, it turns out that a successful description of data can only be achieved with additional assumptions – in our case, they involve the use of projected thermal vorticity and a suitably adjusted time for spin relaxation ($\tau_s$). From our analysis, we find that $\tau_s$ ∼ 5 fm/c, which is comparable with other estimates.

Based on: arXiv 2405.05089 [hep-ph]

Orateur: M. Samapan Bhadury (Jagiellonian University)

13:00 Lunch break

Hydrodynamics: Session 3

Président de session: Masoud Shokri (Goethe University)

64 Non-relativistic transport from frame-indifferent kinetic theory

I will present the application of Newton-Cartan geometry to the kinetic theory of gases in gravitational fields. Starting with an introduction to the basics of Newton-Cartan geometry, I will examine the motion of point particles within this framework, leading to a detailed analysis of kinetic theory and the derivation of conservation equations. The equilibrium distribution function will explored, culminating in a practical example involving a rotating gas in a gravitational field. Further, we will develop covariant hydrodynamics equations and extend our analysis through a gradient expansion approach to assess first-order constitutive relations. This allows us to derive the viscous transport for rotating gases in a consistent way. Finally, we will address the frame-dependence paradox, presenting a novel resolution that explains apparent discrepancies in the literature. Our construction resolves a fifty-year-old debate about the frame-indifferent formulation of kinetic theory.

Orateur: Piotr Surówka

65 Anomalous Hall instability in chiral magnetohydrodynamics

The quark gluon plasma(QGP) is expected to exhibit a chiral imbalance known as the chiral anomaly which induces various anomalous currents, such as: the chiral magnetic effect(CME), the chiral vortical effect(CVE), the anomalous Hall effect(AHE) and so on. To describe these anomalous effects, one can use the chiral magnetohydrodynamics (CMHD).

We study the collective excitations and instabilities in a CMHD and focus on the anomalous Hall instability(AHI) which is due to the AHE in this talk.

Like the CME’s instability, the AHI is dependent on the value of k and appears in a limited scope which is decided by the AHE coefficient $\xi_{H}$. Notably, the AHE does not trigger an instability by itself in a pure electrodynamic context without fluid, but it does in the CMHD. For small |k| expansion, we show that the Alfven wave modified by the AHE leads to an unstable solution. In particular, one can introduce an axion
field $\theta(x)$ which interacts with the electromagnetic field in the form of $\theta E \cdot B$, to reproduce the AHE $\nabla\theta\times E$, the chiral chemical potential $\mu_{5}(x)\equiv\partial_{t}\theta$, where $E,B$ are electric and magnetic fields, the AHE coefficient is $\xi_{H}\equiv \nabla \theta$. Because the AHI happens in a small scope and the total helicity is conserved, these give rise to a novel type of inverse cascade: the fermionic helicity will be transferred to various helicities of the small |k| modes. Then the AHI ceases eventually by depleting the value of $\mu_{5},\xi_{H}$.

Finally, we briefly discuss three different instabilities such as: the chiral plasma instability(CPI), the chiral magnetovortical instability(CMVI), the AHI and the possible relevance in QGP and other physical systems.

Orateur: Shuai Wang

66 Relativistic stochastic advection diffusion equation using Metropolis

We present a method for simulating the stochastic relativistic advection-diffusion equation using the Metropolis algorithm. This approach simulates dissipative dynamics by randomly transferring charge between fluid cells, combined with ideal hydrodynamic time steps. Charge transfers are accepted or rejected based on entropy as a statistical weight in a Metropolis step. This reproduces expected dissipative strains in relativistic hydrodynamics within a specific hydrodynamic frame known as the density-frame. Numerical results, with and without noise, are compared to relativistic kinetics and analytical expectations. Notably, unlike other numerical approaches, this method is strictly first order in gradients and lacks non-hydrodynamic modes. The simplicity and convergence properties of the Metropolis algorithm make it promising for simulating stochastic relativistic fluids in heavy ion collisions and critical phenomena.

Orateur: Dr Rajeev Singh (West University of Timisoara)

The stochastic relativistic advection diffusion equation from the Metropolis algorithm

16:00 Coffee break

General: Conclusions