19th International Conference on QCD in Extreme Conditions (XQCD 2023)

26 Jul 2023, 06:45 → 28 Jul 2023, 18:00 Europe/Lisbon

Auditorium C.1 (Department of Physics (University of Coimbra))

Brigitte Hiller (University of Coimbra), Constança Providência, Michael Strickland (Kent State University), Márcio Ferreira (University of Coimbra), Orlando Oliveira, Paulo Silva, Pedro Costa (CFisUC, University of Coimbra)

The 19th International Conference on QCD in Extreme Conditions (XQCD 2023) will take place from 26 to 28 of July 2023 at the Department of Physics of the University of Coimbra, Portugal. 

XQCD is a series of international workshop-style conferences, held annually, which aims at covering recent advances in the theory and phenomenology of QCD under extreme conditions of temperature and/or baryon density, together with related topics.

We will have 6 invited talks and approximately 30 contributed talks covering the topics:

QCD at Finite Temperature and Density 
Heavy Ion Collisions Phenomenology 
Phase Diagram of Strongly Interacting Matter 
Properties of the Quark-Gluon Plasma 
Properties of Strongly Interacting Gauge Theories 
Machine learning and QFT  
QCD in External Fields 
Neutron stars

Accompanying the XQCD 2023 will take place the 2023 XQCD PhD school on Extreme Conditions. 

Invited speakers:

• Gert Aarts - University of Swansea;
• Jens O. Andersen - Norwegian University of Science and Technology (NTNU);
• Raffaele Del Grande - Technical University of Munich;
• Joseph Kapusta - University of Minnesota;
• Peter Petreczky - Brookhaven National Laboratory;
• Isaac Vidaña - INFN Catania.

 

There will be a fee of 130 € that covers lunches, coffee breaks, and logistics. 
A possible reduced early-bird fee will be considered and advertised in the conference webpage.

A workshop dinner will be organized on Thursday the 27th of July.
The workshop dinner will be approximately 30 €.

There will be a visit to the University Old Library: http://visituc.uc.pt/en/library/ 

Important dates:

Deadline abstract submission: May 15 2023
Notification of acceptance of talk: June 1 2023
Deadline on-line registration: June 15 2023

Registration and abstract submission has been opened on March 1 2023.
 

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Group photo:

 

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Our sponsors are:

         

 

 

Wednesday, 26 July

08:15 Registration

1 XQCD Conference: Welcome and Opening

Invited Speaker Session: 1, Chair: Constança Providência

2 Anomalous kaon correlations measured in Pb-Pb collisions at the LHC as evidence for the melting and refreezing of the QCD vacuum

Measurements of the dynamical correlations between neutral and charged kaons in central Pb-Pb collisions at √s_NN = 2.76 TeV by the ALICE Collaboration display anomalous behavior relative to conventional heavy-ion collision simulators. We consider other conventional statistical models, none of which can reproduce the magnitude and centrality dependence of the correlations. The data can be reproduced by either strange Disoriented Chiral Condensates or by non-strange Disoriented Isospin Condensates from domains which grow in number and volume with increasing centrality.
Both mechanisms are associated with the melting and refreezing of the QCD vacuum.

Speaker: Joseph Kapusta (Minnesota University)

XQCD2023_Kapusta.pdf

3 Machine learning for lattice field theory and back

Recently, machine learning has become a popular tool to use in fundamental science, including lattice field theory. Here I will review on some recent ideas, including normalising flow, phase classification and quantum-field theoretical machine learning. The latter combines insights of lattice field theory and machine learning to provide a fresh perspective on (hopefully) both.

Speaker: Gert Aarts

talkxqcd-aarts.pdf

10:30 Coffee break

Plenary session: 1, Chair: Gert Aarts

4 Building a realistic neutron star from holography

I will present latest results within the holographic Witten-Sakai-Sugimoto model for dense matter at nonzero baryon and isospin chemical potentials. In particular, I will discuss the phase structure including phases where baryonic matter and meson condensates coexist. As an application I will show that the results can be used to construct entire neutron stars, including the inhomogeneous crust. These 'holographic stars' obey the astrophysical constraints on mass, radius, and tidal deformability and can be used to make further predictions for these quantities.

Speaker: Andreas Schmitt (University of Southampton)

schmitt.pdf

5 Topology and robustness of a quark matter phase candidate for magnetars core

One central question in nuclear astrophysics nowadays is determining the matter structure of neutron stars (NS). With the wealth of newly available and upcoming astrophysical observations, it is of most relevance to find ways to compare the characteristics of potential NS matter phase candidates with those gathered from NS observations. As part of these efforts, I will discuss how some unique topological properties of a spatially inhomogeneous, dense quark matter phase in a magnetic field lead to robustness and resilience against thermal phonon fluctuations, making it a plausible candidate for magnetars’ inner core matter.

Speaker: Vivian Incera (University of Texas Rio Grande Valley)

Incera-XQCD23.pdf

6 The critical endpoint at large N_c

The phase diagram of QCD is investigated by varying number of colors N_c within a Polyakov loop quark-meson chiral model. In particular, our attention is focused on the critical point(s); the critical point present for N_c=3 moves toward the mu_q-axis and disappears as soon as the number of color is increased. Yet, a distinct critical point emerges along the temperature axis for N_c=53 and moves toward finite density when increasing N_c further. Thus, the phase diagram at large N_c looks different than the N_c=3 results, since in this case the first-order transition is in the upper-left, while the crossover is in the lower-right regions of the (mu_B-T)-plane. The N_c dependent pressure is also evaluated, which shows a scaling with N_c^0 in the confined and chirally broken phase and with N_c^2 in the deconfined one. Moreover, a chirally symmetric but confined “quarkyonic phase” can be seen at large density and moderate temperature with a pressure proportional to N_c.

Speaker: Dr Péter Kovács (Wigner Research Centre for Physics)

XQCD_2023_pkovacs.pdf

12:15 Lunch

Parallel session A: 1, Chair: Carolyn Raithel

7 Is matter inside massive neutron stars not hadronic?

The behavior of the nuclear equation of state (EOS), which plays a crucial role in describing the properties of neutron stars (NSs), is extensively investigated using a Bayesian approach applied to various classes of relativistic mean field models. These models encompass density-dependent meson couplings (DDH), interactions with non-linear characteristics, and the Chiral Mean Field (CMF) Model. By employing Bayesian analysis, we explore the parameter space of these models and assess their compatibility with observational data. The Bayesian framework employed in this study incorporates a few essential nuclear saturation properties, such as binding energies, symmetry energy as well as constraints from the observation of neutron stars with masses exceeding 2M⊙. Furthermore, the equation of state at low densities, specifically the pure neutron matter EOS, is included by utilizing a precise N3LO calculation within chiral effective field theory.

One of the key aspects examined in this investigation is the possible presence of hyperons within neutron stars and how different sets of models account for their onset. Hyperons are exotic particles containing strange quarks that may appear at high densities. By comparing the predictions of various models, we can discern whether hyperons are likely to exist within neutron stars and assess their influence on the EOS.

Our approach based on microscopic models of hadronic matter allows us to discuss the composition of neutron stars and to establish a reference with respect to agnostic descriptions of the equation of state connecting the low-density EoS to perturbative quantum chromodynamics (pQCD) results, which aim at identifying signatures of deconfinement.

We analyze the compatibility of the different models considered with pQCD, which provides a framework for understanding the strong nuclear force at high energies. We can evaluate the degree to which the hadronic models studied are aligned with fundamental particle physics principles by looking at the agreement between them and pQCD. Additionally, measures of conformality and the normalized trace anomaly are calculated for the model sets under consideration.

The findings of our study indicate that pQCD favors models that exhibit a substantial contribution from the nonlinear vector field term or incorporate hyperons. This suggests that the inclusion of these features in the models leads to better agreement with fundamental principles and observations. We consider that a thorough discussion of the hadronic EOS will help identify a deconfinement phase transition.

Speaker: TUHIN MALIK (CFisUC - University of Coimbra)

XQCD_TMalik.pdf

8 Neutron star radial oscillations with Delta Baryons

Employing the density-dependent relativistic mean-field model, we investigate the effect of delta baryons on the radial oscillations of neutron and hyperon stars. A unified approach is employed to calculate the baryon-meson coupling constants for the spin-1/2 baryonic octet and the spin-3/2 decuplet. By solving the Sturm-Liouville boundary value problem and verifying its validity, we calculate the 20 lowest eigenfrequencies and related oscillation functions of delta-admixed nuclear (N$\Delta$) and hyperonic matter (NH$\Delta$).
We see that the presence of the delta and hyperonic admixtures causes the lowest mode frequencies for N+$\Delta$ and N+H EoSs to be higher than those for the pure nucleonic matter [1]. With the inclusion of hyperons and $\Delta$s, the distance between succeeding modes also increases.

References

1. Ishfaq A. Rather, K. D. Marquez, G. Panotopoulos, I. Lopes, arXiv preprint arXiv:2303.11006 (2023).

Speaker: Dr Ishfaq Ahmad Rather (Centro de Astrofisica e Gravitacao-CENTRA, Instituto Superior Tecnico-IST, Universidade de Lisboa-UL, Av. Rovisco Pais, 1049-001 Lisboa, Portugal)

Ishfaq.pdf

9 Delta baryons in (hot) neutron stars

By applying a relativistic mean-field description of neutron star matter with density dependent couplings, we analyse the properties of nucleonic matter with delta baryons and nucleonic matter with hyperons and delta baryons. We calculate the baryon-meson coupling constants for the spin-1/2 baryonic octet and spin-3/2 decuplet in a unified approach relying on symmetry arguments such as the fact that the Yukawa couplings, present in the Lagrangian density of the Walecka-type models, must be an invariant under SU(3) and SU(6) group transformations. The coupling constants of the baryon with the scalar σ meson are fixed to reproduce the known potential depths for the hyperons and Δ resonances, in an approach that can be extended to all particles. We then apply the calculated coupling constants to study neutron star matter with hyperons and deltas admixed to its composition. We conclude that the Δ- is by far the most important exotic particle that can be present in the neutron star interior. It is always present, independent of the chosen parameterization, and might appear in almost every known neutron star, once its onset happens at very low density. Yet, its presence affects the astrophysical properties of the canonical 1.4 Mo star, and, in some cases, it can even contribute to an increase in the maximum mass reached. We also study the nuclear isentropic equation of state for a stellar matter composed of nucleons, hyperons, and Δ-resonances. We investigate different snapshots of the evolution of a neutron star, from its birth as a lepton-rich protoneutron star in the aftermath of a supernova explosion to a lepton-poor regime when the star starts cooling to a catalyzed configuration. We observe that Λ is the dominant exotic particle in the star at different entropies for both neutrino-free and neutrino-trapped stellar matter. For a fixed entropy, the inclusion of new particles (hyperons and/or delta resonances) in the stellar matter decreases the temperature. Also, an increase in entropy per baryon (1to2) with decreasing lepton number density (0.4to0.2) leads to an increase in stellar radii and a decrease in its mass due to neutrino diffusion. In the neutrino transparent matter, the radii decrease from entropy per baryon 2 to T=0 without a significant change in stellar mass.

Speaker: Kauan Marquez (Universidade de Coimbra)

presentation.pdf

Parallel session B: 1, Chair: Feliciano de Soto

10 Towards a universal description of hadronic phase of QCD

Mean-field model quantum field theories of hadrons were traditionally developed to describe
cold and dense nuclear matter and are by now very well constrained
from the recent neutron star merger observations. We show that when
augmented with additional known hadrons and resonances
but not included earlier, these mean-field models can be extended beyond
its regime of applicability. Calculating some specific ratios of baryon
number susceptibilities for finite temperature and moderate values of
baryon densities within mean-field approximation, we show that these match
consistently with the lattice QCD data available at lower densities, unlike
the results obtained from a non-interacting hadron resonance gas model. We also estimate the
curvature of the line of constant energy density, fixed at its corresponding value
at the chiral crossover transition in QCD, in the temperature-density plane. The
number density at low temperatures and high density is found to be about twice the
nuclear saturation density along the line of constant energy density of $\epsilon=348 \pm 41$ MeV/$\text{fm}^3$. Moreover from this line we can indirectly constrain the
critical end-point of QCD to be beyond $\mu_B=596$ MeV for temperature $\sim 125 $ MeV.

Speaker: Dr Aman Abhishek (Institute of Mathematical Sciences, Chennai, India)

Towards_a_universal_hadronic_description_of_chiral_symmetry_broken_phase_of_QCD (4).pdf

11 QCD equation of state at finite isospin density from the linear sigma model with quarks

Present abstract is based on our recent work [1] where we use the two-flavor linear sigma model with quarks to study the phase structure of isospin asymmetric matter at zero temperature. The meson degrees of freedom provide the mean field chiral- and isospin-condensates on top of which we compute the effective potential accounting for quark fluctuations at one-loop order. Using the renormalizability of the model, we absorb the ultraviolet divergences into suitable counter-terms that are added respecting the original structure of the theory. These counter-terms are determined from the stability conditions which require the effective potential to have minima in the condensates directions at the classical values, as well as the transition from the non-condensed to the condensed phase to be smooth as a function of the isospin chemical potential. We use the model to study the evolution of the condensates as well as the pressure, energy and isospin densities and the sound velocity as functions of the isospin chemical potential. The approach does a good average description up to isospin chemical potentials values not too large as compared to the vacuum pion mass.

[1] - QCD equation of state at finite isospin density from the linear sigma model with quarks: The cold case ; Alejandro Ayala, Aritra Bandyopadhyay, Ricardo L.S. Farias, Luis A. Hernández, José Luis Hernández ; Phys. Rev. D. 107 (2023), 074027 ; 2301.13633 [hep-ph]

Speaker: Aritra Bandyopadhyay

aritra_xqcd23.pdf

12 Towards a Stability Analysis of Inhomogeneous Phases in QCD

Understanding the phase structure of Quantum Chromodynamics (QCD) is of paramount importance for nuclear and particle physics. At large densities and low temperatures, many complex phases are expected to appear. This is where the lattice sign problem is unavoidable and extrapolation methods such as Taylor expansions are out-of-bounds. Alongside colour-superconductivity, quarkyonic matter, and so on, the possibility of a crystalline phase has been studied for over twenty years. In simplified models of QCD such as NJL or quark-meson models, these phases are present. However, no unambiguous determination exists that they appear in QCD. In our work, we develop a method of stability analysis that is compatible with full QCD via Dyson-Schwinger Equations. We present some results for homogeneous phase transitions which illustrate well how the method works and discuss what is to be done for a definite stability analysis of inhomogeneous phases in QCD.

Speaker: Theo Motta (Justus Leibig University Gießen)

TheoMotta_Coimbra.pdf

Parallel session C: 1, Chair: Brigitte Hiller

13 Recent results from NA61/SHINE on the onset of deconfinement studies and particle production

NA61/SHINE at the CERN SPS is a fixed-target experiment pursuing a rich physics program. The main goal of the NA61 ion program is to explore the most interesting region of the phase diagram of strongly interacting matter. Within the expected (T - mu_B) interval we plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. Such a 2D scan of the phase diagram is performed by varying beam momentum (13A-150(8)A GeV/c) and system size (p+p, p+Pb, Be+Be, Ar+Sc, Xe+La, Pb+Pb).

Thanks to its large acceptance and reasonable particle identification NA61/SHINE is well-suited for studies of particle production mechanisms. In this contribution results on the onset of deconfinement as well as on particle production will be reported.

Speaker: Maja Katarzyna Mackowiak-Pawlowska (Warsaw University of Technology (PL))

xqcd2023_slides_mmp.pdf

14 K- nunleon/nuclei interactions studies by AMADEUS at DAFNE

K- nunleon/nuclei interactions studies by AMADEUS at DAFNE

Experimental investigation of the strong interaction in the low-energy regime is mandatory to constrain models of the low-energy meson-baryon interaction, with implications in several fields, ranging from the search for exotic mesic nuclear bound states, to the structure of compact astrophysical objects like the neutron stars. 
In this talk we will review the studies performed by the AMADEUS experiment, at the DAFNE collider of LNF-INFN, of the low-energy kaon-nucleon/nuclei interaction processes. More in detail we will report on the measurement of the non-resonant hyperon pion formation amplitude below the K-N threshold, of the branching ratios and of the low-energy cross sections of the K- multi-nucleon absorptions on various light nuclear targets. The recent, precise, determination of the K$^{-}$p $\rightarrow (\Sigma^{0}/\Lambda) \, \pi^{0}$ cross sections close to threshold will be shown. Future perspectives on the measurement of two- and three-body hyperon-nucleon interaction will be outlined.

Speaker: Dr Kristian Piscicchia (CREF, LNF (INFN))

XQCD2023piscicchia.pdf

15 Transient effects of charge diffusion on electromagnetic field in heavy-ion collision

We study charge diffusion in relativistic resistive second-order dissipative magnetohydrodynamics. In this theory, charge diffusion is not simply given by the standard Navier-Stokes form of Ohm’s law, but by an evolution equation which ensures causality and stability. This, in turn, leads to transient effects in the charge-diffusion current, the nature of which depends on the particular values of the electrical conductivity and the charge-diffusion relaxation time. The ensuing equations of motion are of so-called stiff character, which requires special care when solving them numerically. To this end, we specifically develop an implicit-explicit Runge-Kutta method for solving relativistic resistive second-order dissipative magnetohydrodynamics and subject it to various tests. We then study the system’s evolution in a simplified 1+1-dimensional scenario for a heavy-ion collision, where matter and electromagnetic fields are assumed to be transversely homogeneous, and investigate the cases of an initially nonexpanding fluid and a fluid initially expanding according to a Bjorken scaling flow. In the latter case, the scale invariance is broken by the ensuing self-consistent dynamics of matter and electromagnetic fields. However, the breaking becomes quantitatively important only if the electromagnetic fields are sufficiently strong. The breaking of scale invariance is larger for smaller values of the conductivity. Aspects of entropy production from charge-diffusion currents and stability are also discussed.

Speaker: Ashutosh Dash (Frankfurt University)

XQCD_Ashutosh.pdf

15:15 Coffee break

Parallel session A: 2, Chair: Fernando Navarra

16 Relativistic description of neutron star matter with latest experimental and observational constraints

Astrophysical observations of neutron stars allow us to study the physics of matter at extreme conditions which are beyond the scope of any terrestrial experiments. In this work, we perform a Bayesian analysis putting together the available knowledge from the nuclear physics experiments, observations of different X-ray sources, and gravitational wave events to constrain the equation of state of supranuclear matter. In particular, we employ a covariant density functional to incorporate the uncertainties of the saturation properties of nuclear matter i.e. the symmetry energy and its slope parameter, the incompressibility, the effective mass of the nucleon, the binding energy per nucleon, and the saturation density. Then, we investigate whether it is possible to reconcile the inferred values of those quantities from the multimessenger data, and finally compute a joint posterior distribution of these quantities incorporating all the available knowledge.

Speaker: Prasanta Char

char.pdf

17 What is the nature of the HESS J1731-347 compact object? Does it confirm the early deconfinement phase transition?

Compact stars are the most exotic and dense laboratories in the Universe to test the properties of strongly interacting matter. Understanding the complex phenomena observed in neutron and hybrid stars requires profound knowledge in a wide range of scientific disciplines. In addition to the experimental data on nuclear and hadron matter, the realistic equation of state (EoS) should be consistent with the astrophysical, and gravitational wave observations. While details of the phase transitions and properties of quark matter are traditionally investigated in the accelerator experiments on heavy-ion collisions, compact astrophysical objects recently gained a big interest since observational data on their radii, masses, surface temperature, etc. significantly constrain the properties of strongly interacting matter. We will discuss the recently announced lightest compact star HESS J1731-347 which has raised a lot of questions about its nature. We will show the use of the latest data on the mass, radius, and surface temperature together with the multi-messenger observations of neutron stars and their mergers to investigate the possibility that HESS J1731-347 is the lightest observed neutron star, a strange star, a hybrid star with an early deconfinement phase transition, or a dark matter admixed compact star.

Speaker: Dr Violetta Sagun (University of Coimbra)

Sagun_xQCD.pdf

18 Rebuilding Neutron Star EoSs from Observations with Deep Learning

We present a novel deep learning approach to optimize the equation of state (EoS) for probing neutron star observables. By leveraging an automatic differentiation framework, our method solves inverse problems and achieves accurate EoS optimization. Through training a neural network on a comprehensive dataset, we develop a predictive EoS model that yields precise relationships between pressure, speed of sound, and mass density. Our results align with conventional approaches and are consistent with the observed tidal deformability from the gravitational wave event, GW170817.

Speaker: Lingxiao Wang (Frankfurt Institute for Advanced Studies (FIAS))

XQCD_slides_lingxiao_20230726.pdf

Parallel session B: 2, Chair: Massimo Mannarelli

19 QCD with fundamental and adjoint matter

Strongly-coupled gauge theories with fermions and/or scalars in mixed representations are endowed with a wealth of intricate phase structures. In this talk, I discuss the faithful global symmetries and 't Hooft anomalies of Quantum Chromodynamics (QCD) with matter in the fundamental-adjoint mixed representation. Then, I show how one can utilize the anomalies and effective field theory techniques to construct the infrared phase diagrams of this class of theories. The discussion covers the implications of the limiting scenarios of heavy adjoint or fundamentals, which align neatly with our current understanding of QCD with solely fundamental or adjoint matter.

Speaker: Dr Mohamed Anber (Durham University)

QCD(F:adj)6.pdf

20 Interferometry in a Moat Regime

The QCD phase diagram at large chemical potential is largely uncharted territory. Based on model studies, there are various phases that could occur in this regime. Among them are phases related to spatial modulations, such as inhomogeneous/crystalline phases, liquid crystals or a quantum pion liquid. A common feature of all these phases is that particles can have a moat dispersion, where the energy is minimized at nonzero momentum. This can directly affect particle production in heavy-ion collisions and leads to characteristic signatures in particle correlations. I will discuss the underlying physics and present a formalism to study particle spectra on general hypersurfaces in a medium. Using this formalism, I will show that the correlations generated by the Hanbury-Brown-Twiss effect are promising probes for a moat regime in heavy-ion collisions.

Speaker: Fabian Rennecke (Institute for Theoretical Physics Justus Liebig University Giessen)

XQCD2023_Rennecke.pdf

Parallel session C: 2, Chair: Cristina Manuel

21 Observable consequences of partial thermalization in relativistic nuclear collisions

The discovery of flow-like azimuthal correlations in pA and high-multiplicity pp collisions raises profound questions about the onset of collective flow and its relation to hydrodynamics. We seek independent experimental information on the degree of thermalization in order to identify those hydrodynamic collision systems in which flow is sensitive to equilibrium QCD properties. We aim to develop a protocol for identifying the degree of thermalization using a combination of momentum and multiplicity correlation. To study the effect of thermalization on these correlations, we use Boltzmann equation in the relaxation time approximation with Langevin noise. We derive a new non-equilibrium transport equation for the two-body distribution function that is consistent with the conservation laws obeyed by microscopic scattering processes. We find that transverse momentum fluctuations in peripheral PbPb collisions at LHC markedly deviate from equilibrium behavior. We propose new measurements that can provide more refined information. *This work is supported in part by NSF-PHY1913005 (G.M.)

Speaker: Prof. George Moschelli (Lawrence Technological University)

Moschelli_xqcd2023.pdf

22 Insights from D-meson femtoscopy using T-matrix calculations

In this presentation I will unveil our initial findings on $D$-meson / light-meson femtoscopy. Our analysis employs unitarized effective hadron interactions derived from an off-shell $T$-matrix calculation in a coupled-channel framework. We have obtained the correlation function of heavy-light mesons accounting for Coulomb interaction in the relevant channels, and have analyzed the impact of inelastic processes. I will present a set of results that can be directly compared with experimental data from the ALICE experiment. These involve net strangeness like $D^+K^+$ (+ charge conjugate) and $D^+K^-$ (+ charge conjugate) and zero strangeness like $D^+\pi^+$ (+ charge conjugate) and $D^+\pi^-$ (+ charge conjugate). Additionally, our study encompasses predictions involving novel channels involving $D_s$ mesons. Our original research contributes to a deeper understanding of heavy meson-light meson interactions via femtoscopy measurements.

Speaker: Juan Torres-Rincon (Universitat de Barcelona)

XQCD23_16_9.pdf

XQCD23_4_3.pdf

23 IAC meeting

Poster session

24 Systematic analysis of the impacts of symmetry energy parameters on neutron star properties

The impacts of various symmetry energy parameters on the properties of
neutron stars (NSs) have been recently investigated, and the outcomes are
at variance, as summarized in Table III of Phys. Rev. D 106, 063005 (2022).
We have systematically analyzed the correlations of slope and curvature
parameters of symmetry energy at the saturation density ($\rho_0=0.16 \text{fm}^{-3}$) with the tidal deformability and stellar radius of
non-spinning neutron stars in the mass range of $1.2 - 1.6 M_\odot$
using a large set of minimally constrained equations of state (EoSs).
The EoSs at low densities correspond to the nucleonic matter
and are constrained by empirical ranges of a few low-order nuclear matter
parameters from the finite nuclei data and the pure neutron matter EoS
from chiral effective field theory. The EoSs at high densities ($\rho > 1.5 - 2\rho_0$) are obtained by a parametric form for the speed of sound that
satisfies the causality condition. Several factors affecting the
correlations between the NS properties and the individual symmetry energy parameters usually encountered in the literature are considered. These correlations are quite sensitive
to the choice of the distributions of symmetry energy parameters and
their interdependence.
But, variations of NS properties with the pressure of $\beta -$ equilibrated matter at twice the saturation density remain quite robust which
maybe due to the fact that the pressure depends on the combination of
multiple nuclear matter parameters that describe the symmetric nuclear
matter as well as the density dependence of the symmetry energy.
Our results are practically insensitive to the behavior of EoS at high
densities.

Speaker: Naresh Kumar Patra

25 Analyzing the speed of sound in neutron stars using machine learning

Sagnik Chatterjee, IISER Bhopal
The matter at Neutron star (NS) cores are at highly compressed state and
due to gravity, the density can be built up to a few times the nuclear
saturation density. They are very compact and have been observationally
identified with pulsars with their mass being in the range from 0.7 - 3 solar
masses and a radius between 10-15 km. They are therefore one of the best
laboratories to test the theory of strong interaction at high-density low
temperature regimes. The information about the structure of an NS can be
given by their equation of states (EoSs). At high densities, the first
principle pQCD calculations are consistent and at lower densities field
theory calculations are consistent. The central density of the NS lies
somewhere between these two densities and in this regime the lattice QCD
calculations fail. Hence, we need to resort to model-based or agnostic
approaches to construct EoSs. In this talk, I will present how we can
effectively create several new EoSs from the information on the speed of
sound. Using the created EoSs, we create several datasets to train our
neural network. I will also talk about the neural network model using
which we can effectively predict a new EoS. Using these we study the
variation in the speed of sound inside the NS.

Speaker: Sagnik Chatterjee (Indian Institute of Science Education and Research Bhopal)

26 Volume dependence of the critical endpoint and the baryon number fluctuations

While in field theoretical calculations, being performed in the thermodynamic limit, the volume is infinite, the heavy-ion collisions always carry the effects of finite system size. It is expected that a sufficiently small volume can affect the thermodynamics and the phase diagram of the strongly interacting matter. These effects can be studied in effective models by taking into account the finite spatial extent of the system via the restriction of the momentum integrals with discretization or simpler using a low momentum cutoff. We investigated the finite-size effects in a vector meson extended Polyakov quark-meson model with both scenarios. It was found that the resulting modification of the phase diagram is highly influenced not just by the chosen momentum space constraint and the boundary condition but more importantly by the treatment of vacuum size. Our results also explain certain differences between previous calculations on finite-volume effects within different effective approaches. Moreover, we also studied the volume dependence of the baryon fluctuations both at vanishing baryochemical potential and in the neighborhood of the critical endpoint.

Speaker: Győző Kovács (Wigner Research Centre for Physics)

27 Baryonic screening masses at high temperatures from lattice QCD

We present the first non-perturbative calculation on the lattice of the baryonic screening masses in a wide range of temperature from $1$ GeV up to $T\sim 160$ GeV. The calculation has been carried out by Monte Carlo simulations and exploits a new strategy to simulate extremely high temperatures which was recently used to compute the non-singlet mesonic screening spectrum for the first time in the same range of temperatures. The baryonic screening masses have been computed with a few permille accuracy in the entire range of temperatures. On one hand the bulk of the masses is given by the free theory value $3\pi T$ plus a few percent contribution due to interactions which is still visible even at the highest temperature we simulated. On the other hand chiral symmetry restoration manifests itself through the degeneracy of the parity partners screening masses, as expected by Ward identities associated with the presence of chiral symmetry.

Speaker: Davide Laudicina (Università degli Studi di Milano-Bicocca & INFN)

28 Chiral magnetic waves in quark matter inside neutron stars and gravitational waves

It is important to unravel the internal structure of neutron stars in astrophysics. One effective way to study the interior of neutron stars is analyzing their seismic oscillations. Recently, the chiral magnetic wave (CMW), which is a density wave propagating along magnetic fields due to the chirality of fermions, has been studied in the context of the heavy ion collision experiments.
 In this talk, we show that the CMW can appear as a seismic oscillation in quark matter, such as the two-flavor color superconductivity, inside neutron stars. We also discuss the frequency and amplitude of a new type of gravitational wave radiated by the seismic oscillation. This gravitational wave could be a new probe of the magnetic field and quark matter in neutron stars.

Speaker: Sota Hanai (Keio University)

29 Deconfinement in pure gauge SU(3) Yang-Mills theory: the ghost propagator

The ghost propagator in Landau gauge is studied at finite temperature below and above Tc using lattice QCD simulations. For high temperatures, we find that the ghost propagator is enhanced, compared to the confined phase. The results suggest that the ghost propagator can be used to identify the phase transition, similarly to the gluon propagator case.

Speaker: Paulo Silva

poster_figlong.pdf

30 Determining the EoS of neutron stars using bayesian neural networks

Neutron stars are a remarkable object towards the study of nuclear matter properties under extreme conditions. To extract these properties, we employ Bayesian Neural Networks (BNN) that take Mass-Radius pairs observables as input. The BNN output the speed of sound squared for 15 distinct values of baryonic density energy. Our primary objective encompasses two aspects: obtaining the equation of state for neutron stars and achieving a reliable uncertainty quantification. This allows us to assess the level of confidence in our model predictions and determine if our data is free from noise. Through the implementation of BNNs, we can explore the intricate nature of nuclear matter and go further by extracting the uncertainties that come with it.

Speaker: Valéria Carvalho

31 Does pQCD constrain the neutron star equation?

Knowing the QCD phase diagram is one of the biggest physics challenges we have nowadays.
Neutron stars are true laboratories that test extreme conditions, essential to determine the QCD phase diagram.
In their core, the density can reach $n_B \approx 3 − 8 n_s$ (where $n_s = 0.16 fm^{-3}$ is the saturation density), a range of densities where QCD is unknown.
Ab-initio calculations determine the EoS for densities $n_B > 40 n_s$, where perturbative QCD (pQCD) is valid, and for $n_B < 1.1n_s$, where the EoS is determined using chiral effective field theory (cEFT).
Is it possible to restrict the region of $1.1n_s < n_B < 40n_s$ using the information we have about pQCD and cEFT?
In DOI: 10.1103/physrevlett.128.202701, Komoltsev & Kurkela restrict the unknown region of the QCD phase diagram using thermodynamic relations and the pQCD and cEFT EoS together with i) the causality condition; ii) the thermodynamic relation $n = dP/d\mu$.
We review this work and we apply the constraints to a Relativistic Mean Field (RMF) model.

Speaker: Milena Albino (Universidade de Coimbra)

32 Dynamic critical behavior of the O(4) chiral transition

Evidence suggest that in the chiral limit, the QCD phase transition becomes a second order phase-transition in the $O(4)$ universality class. Since real world QCD is not too far from the chiral limit, it is thus interesting to explore the consequences for static and dynamic correlation functions. Since, in the vicinity of the critical point, the physics is governed by universal scaling exponents and scaling functions, we can exploit this universality to address this question.
We employ classical-statistical real-time simulations to extract the dynamic critical behavior of an O(4) linear sigma model in the static and dynamic universality class of QCD in the chiral limit. By comparing results for the dynamics with and without a conversed energy and O(4) charges, we can realize the Model A and Model G dynamic universality classes in the classification scheme of Halperin and Hohenberg, for which we compute the dynamic critical exponent $z$ of and further extract the relevant dynamic scaling functions for the spectral function of the order parameter.

Speaker: Frederic Klette (Bielefeld University)

33 Dynamics of QCD chiral transition with real-time functional renormalization group

In the chiral limit the complicated many-body dynamics around the second-order chiral phase transition of two-flavour QCD can be understood by appealing to universality. We present a novel formulation of real-time functional renormalization group that describes the stochastic hydrodynamic equations of motion for systems in the same dynamic universality class, which correspond to Model G in the Halperin-Hohenberg classification, and preserves all the relevant symmetries of such systems with reversible mode couplings. We show that the calculations indeed produce the non-trivial value z=d/2 for the dynamic critical exponent, where d is the number of spatial dimensions. We also extract the critical momentum dependence of the charge diffusion coefficient. We keep the degrees of freedom of the order parameters general and show that for N=3 we recover standard Model G dynamics and for N=2 we recover Model E dynamics.

Speaker: Yunxin Ye (Fakultät für Physik, Universität Bielefeld)

34 Exploring the QCD Phase Transitions with Imaginary Rotation

In this talk, I will report our recent achievements based on refs. [1,2]. Below are highlights from our results.

Confinement under Imaginary Rotation
STAR Collaboration found nuclear matter rotating at $\omega \sim 10^{22}\ s^{-1}$ in heavy ion collisions. Neutron stars can also spin at $\omega \sim 10^3\ s^{-1}$. It is interesting but difficult to unravel mysteries in understanding how quarks and gluons behave in rapidly rotating matter. In our study, we considered the Polyakov loop potential at high $T$ with ``imaginary’’ angular velocity. Imaginary rotation provides a well-defined formulation for investigating the QCD phase transition.

Perturbative Realization of Confinement
In ref. [1], we perturbatively calculated the Polyakov loop potential for the imaginary rotating Yang-Mills system. With increasing angular velocity, we found a phase transition to confinement around $\omega/T\simeq i\pi/2$. Furthermore, we argued that this perturbative confined phase can be smoothly connected to the hadronic phase, i.e., the adiabatic continuity can be realized.

Chiral Symmetry Breaking
In ref. [2], we introduce fermions at finite chemical potential and investigated the chiral phase transition. Our results show the spontaneous breaking of chiral symmetry in our previously found confined phase with imaginary angular velocity for any high $T$.

Toward Real Rotation
The physics goal is to analytically continue the results to real rotation, for which the system size must be finite due to the causality condition. In ref. [2], we discuss the boundary condition for the finite size system.

[1] S. Chen, K. Fukushima, and Y. Shimada, Perturbative Confinement in Thermal Yang-Mills Theories Induced by Imaginary Angular Velocity, Phys.Rev.Lett. 129 (2022) 24, 242002.
[2] S. Chen, K. Fukushima, and Y. Shimada, Chiral Symmetry Breaking with Perturbative Confinement at Finite Imaginary Angular Velocity, in completion.

Speaker: Yusuke Shimada (U Tokyo)

35 Extreme plasma physics with QED effects on a quantum computer

Quantum Electrodynamical effects are prevalent in the complex, nonlinear dynamics of plasmas in extreme astrophysical environments (neutron stars, pulsars, black-hole accretion disks) and intense laser interaction with matter. Understanding of these systems has advanced in parallel with the development of the particle-in-cell numerical framework, where the electromagnetic fields created by and interacting with the particles are mediated by a grid, thus reducing the computational complexity. This method shares some similarities with the lattice methods used in QCD/QED: both aim to achieve self-consistency in the simulations, they apply discretization/grid-based representation (either of the phase-space or of space-time), and have the ability to capture collective dynamics.

Despite the success of both numerical frameworks, it is believed that quantum computers can provide significant speedups and memory saving when simulating physical systems. However, these computers are naturally applicable only to a certain kind of problems, that can be expressed in a form equivalent to the linear Schrödinger equation. In the last few years many new algorithms have been designed to map problems that do not strictly satisfy this condition to a quantum circuit. Current general public-access quantum computers only allow for $\sim$20 qubits at a time and short circuit depths ($\sim$100 gates before results get corrupted by decoherence). This has restricted simulation capabilities on real quantum computers to testing toy models for most of the problems of interest. Variational algorithms are promising for the near term quantum computers as they present three main advantages: their circuits are shorter than in regular Hamiltonian simulation, they allow for reconstruction of the wavefunction at each timestep and they can be extended to nonlinear dynamics. While quantum algorithms have been successfully applied in areas such as quantum chemistry and quantum field theory, their study in plasma physics is still at its infancy.

In this work we apply quantum computing techniques to extreme plasma physics scenarios where QED phenomena are present and the dynamics is inherently nonlinear. By bridging the gap between traditional simulation methods and quantum frameworks, we aim to advance our understanding of plasma physics and its connection with quantum field theory.

This work was supported by the Portuguese Science Foundation (FCT) Grants PTDC/FIS-PLA/3800/2021, CEECIND/01906/2018 and UI/BD/153735/2022.

Speaker: Oscar Amaro (GoLP/Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal)

36 From fluid dynamics to RG flow studies of phase transitions

We employ a numerical method borrowed from fluid dynamics to solve functional renormalization group flow equations for systems with multiple competing order parameters. We demonstrate the application of our approach with the aid of zerodimensional quantum field theories which allow us to mimic specific situations also encountered in higher-dimensional theories. Our results suggest that this novel approach indeed represents a promising tool for investigations of spontaneous symmetry breaking and phase transitions in the theory of the strong interaction.

Speaker: Niklas Zorbach

37 Heavy Baryons in Warm Stellar Matter

Light nuclei can be found in core-collapse supernova matter and in binary star mergers. Their presence may impact the evolution of these systems. The presence of degrees of freedom such as hyperons, hyperclusters and Delta isobars may as well impact the composition of these systems at temperatures as high as T~50-100 MeV achieved in both supernova and binary systems.

Speaker: Tiago Custódio (Universidade de Coimbra)

38 Implicit Regularization in a QCD decay of the Higgs boson

Implicit Regularization (IReg) is a regularization scheme that works in the physical dimension of the theory and allows for the separation of the ultraviolet (UV) and infrared (IR) divergences of an amplitude. We compute the Higgs decay into gluons using an effective Higgs–Yang-Mills interaction in the limit of infinite top quark mass by using a dimension five operator. The decay rate for H→gg(g) is calculated in this strictly 4-dimensional set-up to α_s^3 order in the strong coupling. We use
spinor-helicity formalism to include the processes that contribute at the same perturbative order in the real emission channels consisting of 3 gluons and a gluon and quark-antiquark final states with light (zero mass) quarks. Unambiguous identification and separation of UV from IR divergences is achieved putting at work the renormalization group scale relation inherent to the method. UV singularities are removed by renormalization and the IR divergences are cancelled due to the method’s compliance with the Kinoshita-Lee-Nauenberg (KLN) theorem. The remaining finite integral contributions are evaluated using Package-X. We verify that no evanescent fields such as scalars need be introduced as required by some mixed regularizations that operate partially in the physical dimension.

Speaker: Ana Pereira (CFisUC - University of Coimbra)

39 Incorporating Mass Effects of Plasma Constituents in Heavy Fermion Energy Loss Calculations in hot QED and QCD

In this short talk, I will review the energy loss experienced by an energetic fermion with mass (M) traversing a hot QED/QGP plasma at finite temperature (T). These kind of computations were carried for the first time more than 30 years ago by Bjorken, were later reviewed by Braaten and Thoma and more recently by Peshier and Peigné. In those computations, the mentioned authors assumed that the fermionic constituents of the plasma are massless, as this is a reasonable approximation in the scenarios were those computations are relevant.

In our recent work, we generalize those energy loss computations including a perturbative small mass (m) for the plasma constituents, susch that m << T. We also give the necessary ingredients to carry out the computations for values of the mass close to the temperature.

Our findings reveal that for fermion masses around the soft scale eT, mass corrections are in line with pure perturbative corrections. However, as the fermion mass increases, the impact of mass corrections become dominant. Additionally, we assess the implications of these corrections on collisional energy loss in a QCD plasma.

Speaker: Marc Comadran Casas

40 Infrared Subtleties and Chiral Vertices at NLO: An Implicit Regularization Analysis

We employ implicit regularization (IReg) in quark-antiquark decays of the Z, or of a scalar (CP-even or odd) boson at NLO, and compare with dimensional schemes to reveal subtleties involving infrared divergence cancellation and $\gamma_5$-matrix issues. Besides the absence of evanescent fields in IReg, such as $\epsilon$-scalars required in certain schemes that operate partially in the physical dimension, we verify that our procedure preserves gauge invariance in the presence of the $\gamma_5$ matrix without requiring symmetry preserving counterterms while the amplitude is infrared finite as required by the KLN theorem.

Speaker: Ricardo Jorge Carvalho Rosado (CFisUC, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal)

41 Inhomogeneous phases and non-monotonic dispersion relations in strongly-interacting matter

In this talk, I discuss results about inhomogeneous chiral phases, where in addition to chiral symmetry also translational symmetry is broken, and the related moat regimes, where non-monotonic dispersion relations appear driven by a negative wave function renormalization. These phenomena may occur in strongly-interacting matter under extreme conditions such as finite baryon density and temperature. The possibility of inhomogeneous phases and moat regimes is studied in a variety of Four-Fermion and Yukawa theories, which are considered as low-energy effective models of QCD. Using the mean-field approximation, we analyze the stability of homogeneous condensates against inhomogeneous perturbations to draw conclusions about the phase diagrams of these theories. Also, we study the consequences of a negative wave function renormalization with respect to bosonic correlation functions in an effective O(N) model using lattice field theory.

Speaker: Marc Winstel (Goethe University, Frankfurt am Main)

42 Inhomogeneous phases in dense nuclear matter

Quantum Chromodynamics at high densities is likely to exhibit inhomogeneous phases. The chiral density wave is a simple ansatz for a class of such phases, and it has been extensively studied in models based on quark degrees of freedom. We are exploring the possibility of a chiral density wave in a nucleon-meson model, taking into account the contribution of the Dirac sea. We find that for small pion mass, even though in the homogeneous case the chiral transition is a crossover, the chiral density wave is energetically favored in a certain density regime. Our model allows us to link the existence of this regime to the properties of nuclear matter at saturation. For the physical pion mass, we find that the chiral density wave is disfavored and more complicated inhomogeneous configurations may appear.

Speaker: Mr Savvas Pitsinigkos (University of Southampton)

43 Mean field approximation for effective theories of lattice QCD

For the exploration of the phase diagram of QCD, effective Polyakov loop theories derived from lattice QCD provide a valuable tool in the heavy quark mass regime. In practice, the evaluation of these theories is complicated by the appearance of long-range and multipoint interaction terms. On the other hand, it is well known that for theories with such kind of interactions mean field approximations can be expected to yield reliable results. Hence, the evaluation of the effective theories within the mean field framework is discussed.

Speaker: Christoph Konrad (Goethe U., Frankfurt)

44 Mean transverse momentum fluctuations with string percolation model at LHC energies

Initial state effects in Heavy Ion Collisions play an important role in the quark-gluon plasma formation. Moreover, recent experimental studies have shown that these initial state effects become more relevant in small collision systems where the characterization of medium formed is still an open question. We present predictions of the initial state effects on the small collision systems for the mean transverse momentum fluctuations in for pp, pA, OO and pO at LHC energies, as a function of the number of particles produced in the framework of the String Percolation Model Percolation Color Sources and PYTHIA. Where, similarly to nuclei collisions, signatures of a collective medium are observed and strongly suggest quark-gluon plasma formation at small collision systems by observing a change in slope in the region of high multiplicity events.

Speaker: Pablo Fierro Rojas (Autonomous University of Puebla (MX))

45 On gauge equivariant neural networks and global symmetries

Recently, efforts have been increased to incorporate various symmetries into the architectures of neural networks. Lattice gauge equivariant Convolutional Neural Networks (L-CNNs) [1] are designed to respect local gauge symmetry, an essential component in lattice gauge theories. This makes them a promising approximator of gauge covariant functions on a lattice. In addition to local symmetries, many observables exhibit global symmetries. This calls for an extension of the L-CNN beyond translational symmetry to a more general symmetry group, including e.g. rotations and reflections [2].

In this talk, I will review some essential layers of the L-CNN and discuss why they can be used to approximate any gauge equivariant function on the lattice. Then, I will examine how these layers can be generalized to respect not only global translations, but also rotations and reflections. Finally, I will discuss globally and locally equivariant activation functions and pooling layers.

[1] M. Favoni, A. Ipp, D. I. Müller, D. Schuh, Phys. Rev. Lett. 128 (2022), 032003, [arXiv:2012.12901]
[2] J. Aronsson, D. I. Müller, D. Schuh [arXiv:2303.11448]

Speaker: Daniel Schuh (TU Wien)

46 On the application of gauge equivariant neural networks to the generation of field configurations

A strategy that has been increasingly and successfully employed over the last few years in the design of neural network architectures is the implementation of layers that inherently respect a specific symmetry. In the context of lattice gauge theories, local symmetries are a crucial element. Lattice gauge equivariant neural networks (L-CNNs) [1] are designed to preserve such symmetries and have proven to be outperforming traditional convolutional neural networks in the prediction of physical observables. Here, we report our recent developments in the application of L-CNNs to the generation of gauge field configurations. Specifically, we use the framework of neural ordinary differential equations in combination with L-CNNs to modify configurations in a gauge equivariant way.

[1] M. Favoni, A. Ipp, D. I. Müller, D. Schuh, Phys.Rev.Lett. 128 (2022), 032003, [arXiv:2012.12901]

Speaker: Matteo Favoni (Institute for Theoretical Physics, TU Wien, Austria)

47 Pressure of cold quark matter: Next-to-leading logarithm

Accurately understanding the thermodynamics of cold and dense deconfined quark matter plays an essential role in constraining the behavior of QCD matter inside the ultra-dense cores of neutron stars. Indeed, the past few years have witnessed promising steps towards completing the N$^3$LO term in the weak-coupling expansion of the cold and dense QCD pressure. In this talk, I will present the state-of-the-art result for the said quantity up to and including a new $\alpha_s^3\ln\alpha_s$ term. This advancement has been made possible by the recently determined NLO hard-thermal-loop gluon self-energy, allowing the computation of the so-called mixed sector of the pressure arising from the interactions between long- and short-wavelength gluons. The new contribution decreases the uncertainty of the high-density pressure, and I will discuss its implications on the neutron-star equation of state.

Speaker: Kaapo Seppänen

48 Probing hybrid stars and the properties of the special points with radial oscillations

We study the properties of hybrid stars containing a color superconducting quark matter phasevin their cores, which is described by the chirally symmetric formulation of the confining relativistic density functional approach. It is shown that depending on the dimensionless vector and diquark couplings of quark matter, the characteristics of the deconfinement phase transition are varied, allowing us to study the relation between those characteristics and mass-radius relations of hybrid stars. Moreover, we show that the quark matter equation of state can be nicely fitted by the AlfordBraby-Paris-Reddy model that gives a simple functional dependence between the most important parameters of the EOS and microscopic parameters of the initial Lagrangian. Based on it, we analyze the special points of the mass-radius diagram in which several mass-radius curves intersect. To find a distinguishable observational characteristic of the stars with the same mass and radius in the special points and probe their interior composition we calculate the frequencies of the fundamental mode of radial oscillations.

Speaker: Christoph Gärtlein

49 Pseudogauge freedom and the SO(3) algebra of spin operators.

The energy-momentum and spin tensors for a given theory can be replaced by alternative expressions that obey the same conservation laws for the energy, linear momentum, as well as angular momentum but, however, differ by the local redistribution of such quantities (with global energy, linear momentum, and angular momentum remaining unchanged). This arbitrariness is described in recent literature as the pseudogauge freedom or symmetry. In this letter, we analyze several pseudogauges used to formulate the relativistic hydrodynamics of particles with spin 1/2 and conclude that the canonical version of the spin tensor has an advantage over other forms as only the canonical definition defines the spin operators that fulfil the SO(3) algebra of angular momentum. This result sheds new light on the results encountered in recent papers demonstrating pseudogauge dependence of various physical quantities. It indicates that for spin-polarization observables, the canonical version is fundamentally better suited for building a connection between theory and experiment.

Speaker: Sourav Dey (National Institute of Science Education and Research(INDIA))

50 QCD Anderson transition with overlap valence quarks on a twisted-mass sea

In this work we probe the QCD Anderson transition by studying spectral distributions of the massless overlap operator on gauge configurations created by the twisted mass at finite temperature collaboration (tmfT) with 2+1+1 flavors of dynamical quarks and the Iwasaki gauge action. We assess finite-size and discretization effects by considering two different lattice spacings and several physical volumes, and mimic the approach to the continuum limit through stereographic projection. Fitting the inflection points of the participation ratios of the overlap Dirac eigenmodes, we obtain estimates of the temperature dependence of the mobility edge, below which quark modes are localized. We observe that it is well-described by a quadradic polynomial and systematically vanishes at temperatures below the pseudo-critical one of the chiral transition. In fact, our best estimates within errors overlap with that of the chiral phase transition temperature of QCD in the chiral limit.

arXiv-Link to the paper

Speaker: Mr Robin Kehr (Justus Liebig University Giessen)

QCD_Anderson_Poster.pdf

51 Quantum chaos in a minimalistic supersymmetric Yang-Mills-like model: from graviton gas to black holes and black branes

We consider a minimalistic supersymmetric quantum mechanical model with two bosonic and one fermionic degree of freedom, and a Hamiltonian that resembles that of a dimensionally reduced super-Yang-Mills theory. Low dimensionality of the model allows for an exact diagonalization study, which reveals surprisingly rich dynamics. Studying the energy level statistics, we identify three distinct regimes which closely resemble the graviton gas, the Schwarzschild black hole, and the black D0-brane regimes of the holographic dual of compactified 10-dimensional N=1 Super-Yang-Mills theory (BFSS model). All three regimes feature growing Out of Time Order Correlators (OTOCs) and appear to be indistinguishable in thermodynamics observables but exhibit very different behaviors of entanglement entropy.
The model provides an interesting testbed for first-principle studies of quantum chaos in Yang-Mills-like models.

Speaker: Pavel Buividovich

52 Reanalysis of critical exponents for the O(N) model via a hydrodynamic approach to the Functional Renormalization Group

We compute the critical exponents of the O(N) model within the Functional Renormalization Group (FRG) approach. We use recent advances which are based on the observation that the FRG flow equation can be put into the form of an advection-diffusion equation. This allows to employ well-tested hydrodynamical algorithms for its solution. In this study we work in the local potential approximation (LPA) for the effective average action and put special emphasis on estimating the various sources of errors. Our results complement previous results for the critical exponents obtained within the FRG approach in LPA. Despite the limitations imposed by restricting the discussion to the LPA, the results compare favorably with those obtained via other methods.

Speaker: Fabrizio Murgana (Università degli studi di Catania, Goethe Universitat Frankfurt)

53 Renormalization group consistent treatment of neutral color-superconducting matter

The phase diagram of dense matter relevant for neutron stars is typically studied with effective models. These models are nonrenormalizable and must be regularized in order to obtain finite results, leading to regularization artefacts near the cutoff. We study neutral dense matter in a three-flavour Nambu-Jona-Lasinio type model that includes a diquark interaction leading to the formation of color superconducting condensates at high densities. Regularizing the model, e.g. with a sharp three momentum cutoff, leads to a decrease of the color superconducting condensate at large baryon chemical potential. We show how this cutoff artefact can be cured in a renormalization group consistent way based on the scheme developed by Braun et al. We present the resulting phase diagram and give a short outlook on the implications for the neutron star equation of state.

Speaker: Marco Hofmann (Technical University of Darmstadt)

54 Schwinger model at finite temperature and density using quantum imaginary time evolution

We have studied the chiral and confinement-screening phase transitions in the Schwinger model at finite temperature and density using the quantum algorithm.
The theoretical exploration of the phase diagram for strongly interacting systems at finite temperature and density remains incomplete mainly due to the sign problem in the conventional Lattice Monte Carlo method.
However, quantum computation offers a promising solution to circumvent the sign problem as it deals with quantum field theories in the Hamiltonian formalism.
The preparation of thermal states on quantum circuits is a non-trivial challenge.
We have successfully implemented the thermal state preparation on quantum circuits using a theoretical framework known as Thermal Pure Quantum states (TPQs) and the Quantum Imaginary Time Evolution (QITE) algorithm.
The details of the algorithm, our improvements, and the results will be presented in the talk.

Speaker: Mr Juan William Pedersen (University of Tokyo)

55 Spectra and flow of magnetised lepton pairs

Recently, we have calculated the dilepton rate coming out of a hot and dense QCD medium under an arbitrary strength of magnetic field [1]. A considerable amount of enhancement in the rate has been observed in the presence of the magnetic field. We calculate the p_T spectra and the anisotropic flow of dileptons using a hydrodynamical model framework and the new rate [2]. Both spectra and anisotropic flow are found to be affected significantly due to the presence of the background field. We discuss the implications of our findings and the possibility of using magnetised dileptons as magnetometers for heavy-ion collisions.

1. Das et al [Phys. Rev. D 106, 056021 (2022)]
2. Das et al [In preparation]

Speaker: Chowdhury Aminul Islam

56 Speed of Sound of strong-interaction matter at supranuclear densities

Towards the equation of state of neutron stars, we present results for the zero-temperature thermodynamics of strong-interaction matter at high densities which have been obtained based on first-principles functional Renormalization Group studies. In particular, we discuss gluon vacuum polarization effects on the equation of state and the speed of sound in a (semi-)perturbative manner. Eventually, we present consistent constraints for the speed of sound at supranuclear densities by taking into account results from studies based the existence of a (color-) superconducting gap.

Speaker: Andreas Geissel (TU Darmstadt)

57 Study of initial state fluctuations in pp and pPb collisions

Heavy-ion collisions create an environment characterized by extremely high energy density and temperature, leading to the formation of a deconfined state of matter known as quark-gluon plasma (QGP), where quarks and gluons move freely. Recently, collective effects have also been observed in proton-proton (pp) collisions, specifically in events with a high particle production rate. To gain further insights into the origins of these collective effects, the thermal state generated by such collisions is investigated using soft probes.
This study focuses on analyzing the thermal fluctuations of the initial state in collisions involving proton-proton (pp), proton-lead ($pPb$), and lead-lead ($PbPb$) systems at the energies of the Large Hadron Collider (LHC). The aim is to examine the state formed during high multiplicity events in these systems and explore whether it corresponds to the quark-gluon plasma. The analysis includes studying fluctuations associated with the initial state, such as variations in the multiplicity spectrum. This investigation enables the examination of temperature, energy density, and species characterization, both locally and globally, for each collision event.
The analysis is conducted using the Color String Percolation Model (SPM), which proposes transverse momentum fluctuations. The results obtained are compared with the Tsallis distribution, known for its successful representation of transverse momentum spectra in both pp collisions and heavy-ion collisions.

Speaker: Fernando Enrique Neri Huerta (Autonomous University of Puebla (MX))

58 Study of the p$\Lambda$ interaction in small collision systems using a common emission source

In femtoscopy, the correlations between low relative momentum particles can be linked to their emission source function and final state interaction. In a recent precision measurement of the p$\Lambda$ correlation function at the LHC, a deviation was found from the state-of-the-art chiral effective field theory model. If this discrepancy is related to the p$\Lambda$ interaction, it would have important implications for the study of the nuclear equation of state and modeling of neutron stars.

This contribution introduces a new Monte Carlo model, called CECA, capable of evaluating the source function, by generating the spatial and momentum coordinates of single particles in small collision systems, at the time of hadronization. For this purpose, relativistic effects are taken into consideration, as well as the production of particles through intermediate short-lived resonances. Assuming a common emission source for all hadrons, measured proton-proton correlation functions by ALICE are used to constrain the source function. This allows the use of correlation techniques to access the p$\Lambda$ interaction in previously unexplored low-energy regions. The obtained scattering length is smaller than the currently accepted values, highlighting the importance of using femtoscopy data as a complementary way of constraining the theory.

Speaker: Mr Jaime Gonzalez Gonzalez (Technical University of Munich (TUM))

59 Superconducting baryon crystal induced via the chiral anomaly

Determining the phase structure of nuclear and quark matter in external magnetic fields is not only of theoretical interest but also experimentally motivated by the large magnetic fields found in heavy-ion collisions and compact star physics. By including the effects of the chiral anomaly within Chiral Perturbation theory at zero-temperature and non-zero baryon chemical potential, it can be shown that neutral pions form an inhomogeneous phase dubbed the "Chiral Soliton Lattice" (CSL) above a certain critical magnetic field. Above a second, even 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. By applying similar methods originally used by Abrikosov, I will construct an inhomogeneous, superconducting baryon crystal phase existing above this point which is preferred in the chiral limit. An update will be given on current progress of results outside the massless pion approximation.

Speaker: Geraint Evans (Goethe University Frankfurt/ University of Southampton)

60 The Phase Diagram of the Gross-Neveu-Yukawa Modell in (2+1) Space-Time Dimensions using Functional Renormalization Group

In this study, the phase structure of the Gross-Neveu-Yukawa model in (2 + 1) dimensions for $\mu$ and $T$ is explored. This work complements previous works in 1+1 dimensions for finite N and 2+1 mean field as well as finite $N_f$ results (at zero chemical potential). The Functional Renormalization Group is used to calculate the effective potential. With the use of the Local Potential Approximation (LPA), the computation of the effective action can be further simplified to a diffusion type equation with a sink/source. The resulting heat equation is then solved with existing hydrodynamic solving techniques. With this setup, the phase diagram in the $\mu$-$T$ plane is calculated.

Speaker: Keiwan Jamaly

61 The QCD chiral phase transition for various numbers of flavors at imaginary baryon chemical potential

In order to constrain the QCD phase diagram with physical quark masses, the QCD chiral phase transition in the massless limit is investigated, although this is a challenging problem for lattice QCD. In 1984, Pisarski and Wilczek predicted a first-order transition for $N_\text{f}\geq 3$, based on RG investigations of a linear sigma model in three dimensions, which was supported by lattice QCD simulations on coarse lattices. However, recent lattice QCD results from our group provide strong evidence for a second order chiral phase transition for $N_\text{f}=2-6$ massless quark flavors. It was demonstrated that the first-order chiral transitions, observed on coarse lattices, terminate at a tricritical lattice spacing, and are thus not connected to the continuum chiral limit. As a consequence, the chiral transition in the continuum is of second order, as it is always approached from a crossover region. Adopting the same strategy, we investigate the nature of the chiral phase transition as a function of the number of quark flavors and the lattice spacing for a fixed imaginary baryon chemical potential. We find that first-order transitions, observed on coarse lattices, disappear towards the continuum limit, which coincides with the situation at zero density.

Speaker: Reinhold Kaiser

62 Towards the equation of state of color-superconducting strong-interaction matter

We investigate the formation of a color superconductor in dense strong-
interaction matter as associated with the dynamical generation of a gap in
the quark excitation spectrum. To this end, we employ the Wetterich equa-
tion and solve it with numerical methods borrowed from fluid dynamics,
without making any further assumptions about the form of the effective
potential. We critically assess approximation artefacts by comparing qual-
itative and quantitative differences between mean field and local potential
approximation flows.

Speaker: Jonas Stoll (TU Darmstadt)

63 Universality of jet energy loss in the quark-gluon plasma using Bayesian inference

Experimental data on a wide range of jet observables measured in heavy ion collisions provide a rich picture of the modification of jets as perturbative probes and of the properties of the quark-gluon plasma that is formed in these collisions. However, their interpretation is often limited by the assumptions of specific quenching models, and it remains a challenge to establish model-independent statements about the universality of different jet quenching observables.

In this work, we address this issue by proposing a treatment that is agnostic to the details of the jet-medium interactions and relies only on the universality of quark and gluon quenching in different jet observables. We use Bayesian inference to constrain the parameterisation of the energy loss of quark- and gluon-initiated jets in a data-driven manner. This constraint is primarily performed using the inclusive jet pT spectrum, for which the quark/gluon fraction varies across rapidity. We then predict the observed jet asymmetry in di-jet and boson-jet measurements, providing evidence for the universality of quenching effects.

Furthermore, we examine the extracted Casimir scaling of jet quenching and the role of resolution effects in constraining the early, perturbative jet evolution using these data-driven methods. This study provides a new perspective on the universality of jet quenching in heavy ion collisions, free from the assumptions of specific models.

Speaker: Alexandre Falcão (University of Bergen)

64 Unmasking strange dwarfs with gravitational-wave observations

The advent of space-based gravitational-wave detectors like the Laser Interferometer Space Antenna will allow to observe signals most of which are expected to be emitted by white-dwarf binaries. Among these systems could be hidden another kind of compact objects, postulated by Glendenning, Kettner and Weber in 1995, containing a small core made of strange quark matter surrounded by layers of hadronic matter reaching densities much higher than in white dwarfs. These so called strange dwarfs cannot be easily distinguished from white dwarfs through electromagnetic observations alone: their outermost envelopes are expected to have the same composition and their radii are quite similar (except for low masses). However, future measurements of the tidal deformability through gravitational-wave observations could provide a new way to reveal their existence.

Speaker: Loïc Perot

65 Unveiling the shear viscosity to entropy density ratio with gravity analogs

One of the most intriguing aspects of strongly coupled quark gluon plasma is near perfect fluidity observed
in relativistic heavy-ion collisions. One way of quantifying this property is by means of the shear viscosity
to entropy density ratio $\eta/s$. Within the AdS/CFT correspondence, it has been conjectured by Kovtun, Son
and Starinets that a universal lower bound $1/4\pi$ exists. We present a new perspective on this matter in the
framework of analogue gravity models, focusing on relativistic fluids with transonic flow. Quantum fluctuations
at the acoustic horizon, the fluid analog of the event horizon of a black hole, result in a thermal radiation of
phonons, the sonic analog of the Hawking radiation. Adopting a covariant relativistic kinetic theory, we describe
the Hawking emission as a dissipative process. Neglecting phonon’s self interactions, we find the saturation
of $\eta/s$. We connect the KSS bound to the absence of a gap in the low energy spectrum of long-wavelength
excitations.

Speaker: Silvia Trabucco

Thursday, 27 July

Invited Speaker Session: 2, Chair: Lorenz von Smekal

66 Bose condensation in dense QCD

In this talk, I will discuss recent progress in our understanding of pion and kaon condensation in dense QCD. Using chiral perturbation theory at finite isospin and strangeness density, we map out the phase diagram. We also include electromagnetic interactions. The equation of state, speed of sound, chiral and pion condensates are calculated to next-to-leading order in the low-energy expansion. The results are compared to recent high-precision lattice simulations and the results are generally in very good agreement.
We discuss the effective field theory that describes the Goldstone bosons arising from the spontaneous breakdown of U(1)-symmetry.
In the nonrelativistic limit, we recover the classic results for the dilute Bose gas. These include leading corrections to the mean-field result for the energy density as well as the damping rate of phonons.

Speaker: Prof. Jens Oluf Andersen

andersenxqcd23.pdf

67 A novel technique to access the residual strong interaction among hadrons at the LHC

The ALICE collaboration has delivered in recent years unprecedented precision information on the residual strong interaction for several hadron pairs in the strange quark sector. These results have been obtained by analyzing the momentum correlation of particle pairs produced in pp and p-Pb collisions at the LHC. In such colliding systems hadrons are emitted at relative distances of the order of 1 fm, therefore, the effect of the short range strong interaction is reflected in the measured correlation function. This observable has been employed to test for the first time lattice QCD calculations and also to challenge the effective field theory results. In this contribution, the first measurement of the p-ϕ and Λ–K± correlations in high-multiplicity pp collisions at √s = 13 TeV will be shown. The extracted scattering parameters will be presented and the implications for the corresponding theoretical models will be discussed. In particular, evidence of a spin-½ p-ϕ bound state has been recently found by interpreting the measured p-ϕ correlation function with the help of Lattice calculation for the spin 3/2 component. For Λ–K− system, the first experimental evidence of the Ξ(1620) decaying into Λ–K− pairs has been observed, with strong implications on the existing Λ-K̄ interaction models. In the last part of the talk, the extension of such correlation studies by ALICE to the three-body sector will be discussed. It will be demonstrated that three-baryon systems can be precisely measured at the LHC and that light nuclei can be exploited for such studies as well, offering a new opportunity to investigate many-body nuclear forces with innovative methods.

Speaker: Raffaele Del Grande (Technische Universitaet Muenchen (DE))

Talk_Coimbra2023_DelGrande_v5.pdf

10:00 Coffee break

Plenary session: 2, Chair: Efrain Ferrer

68 Magnetic enhancement of baryon confinement modeled via a deformed Skyrmion

The gigantic magnetic field, $B$, is expected in the heavy-ion collision and in the neutron star cores. The phase structure under $B$ has been well investigated, but the hadron properties are not fully understood. Recently, the lattice QCD found that even neutral meson masses are significantly affected by the $B$ effects. Then, what about baryons?

In this talk, I would like to emphasize that the $B$-modified baryon properties are far more nontrivial than naively thought. In particular, I propose a new approach to think about the baryon confinement based on our paper, e-Print:2303.04692 [hep-th].

-- Confinement from the Pressure Balance --

The pressure distribution inside the proton is measurable by the deeply virtual Compton scattering, and the confinement means that the inner positive pressure is balanced by the outer confining negative pressure, i.e.,
$\displaystyle \int d^3 x\,p(x) = 0$,
which can be confirmed in concrete calculations, e.g., in the Skyrme model. This pressure balance is guaranteed by the virial theorem.

-- Magnetic Enhancement of Confinement --

The above sum rule is changed by $B$, in an intriguing way as
$\displaystyle \int d^3 x\,p(x) = -\frac{2}{3}\boldsymbol{\mu}\cdot\boldsymbol{B}$,
where $\mu$ is the magnetic moment. Using the deformed Skyrmion under $B$, we found that $\boldsymbol{\mu}\cdot\boldsymbol{B}<0$, which means that confinement is assisted by an extra pressure from the magnetic field!

In this talk, I will report this novel view of confinement as well as exciting results for the quantization (protons and neutrons), the mass changes, and the magnetic moments as functions of $B$.

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

fukushima.pdf

69 Hydrodynamics of fluctuations and maximum entropy freeze-out

Fluctuations play crucial role in determining properties of the QCD equation of state and transport in heavy-ion collision experiments. Recent progress in understanding evolution of fluctuations in relativistic hydrodynamics aims at providing predictive description of the fluctuations, including their non-gaussianity. The problem of connecting the predictions of hydrodynamics with experimental measurements of fluctuations requires a description of freeze-out which, similar to hydrodynamics itself, fulfills conservation laws on event-by-event basis. The maximum entropy approach elegantly solves this long-standing problem.
[1] An, Basar, Stephanov, and Yee, Phys.Rev.Lett. 127 (2021) 7, 072301 [arxiv:2009.10742]; arxiv/221213029
[2] Pradeep, Stephanov, Phys.Rev.Lett. 130 (2023) 16, 162301 [arxiv:2211.09142]

Speaker: Misha Stephanov (UIC)

xqcd-2023-slides.pdf

70 Jet quenching in glasma

We discuss the transverse momentum broadening of hard probes traversing an evolving glasma, which is the earliest phase of the matter produced in relativistic heavy-ion collisions. The coefficient $\hat q$ is calculated using the Fokker-Planck equation, and an expansion in the proper time $\tau$ which is applied to describe the temporal evolution of the glasma. The correlators of the chromodynamic fields that determine the Fokker-Planck collision terms, which in turn provide $\hat q$, are computed to fifth order in $\tau$. The momentum broadening is shown to rapidly grow in time and reach a magnitude of several ${\rm GeV^2/fm}$. We show that the transient pre-equilibrium phase provides a contribution to the energy loss of hard probes which is comparable to that of the long lasting, hydrodynamically evolving, equilibrium phase.

Speaker: Stanislaw Mrowczynski (National Centre for Nuclear Research, Warsaw, Poland)

XQCD-2023.pdf

71 Helicity conservation in relativistic perfect fluids

We show that in isentropic relativistic fluids the total helicity of a perfect electromagnetic fluid is conserved. The helicity conservation law can be reshaped in the form of a chiral anomaly equation.
For systems made up by massless fermions, we study how the helicity conservation law is modified in the presence of a chiral misbalance, when one has also to consider the effects of the chiral anomaly equation. We discuss on possible consequences of our findings in several systems.

Speaker: Cristina Manuel (Instituto de Ciencias del Espacio (CSIC-IEEC))

XQCD23-good.pdf

12:10 Lunch

13:50 Group Photo

14:00 Visit Old Library

Parallel session A: 3, Chair: Waseem Kamleh

72 Nontrivial topology in QCD, the Vacuum Energy and Large scale magnetic field of the Universe

We discuss the dynamics of the topologically nontrivial sectors with non-trivial holonomy in strongly coupled QCD in the background of the expanding universe characterized by the Hubble scale $H\ll \Lambda_{QCD}$. We argue that the vacuum energy and the de Sitter phase emerge dynamically with the scale $\rho_{DE}\approx H\Lambda_{QCD}^3 \approx (10^{-3} eV)^4$, which is amazingly close to the observed value. We argue that the key element for this idea to work is the presence of nontrivial holonomy in strongly coupled gauge theories. The effect is global in nature and cannot be formulated in terms of a gradient expansion in an effective local field theory. We also argue that anomalous coupling of the dark energy with electromagnetism generates the large cosmological magnetic field correlated on the scale of the visible Universe as observed. We test these ideas with solvable models for QCD being formulated on Hyperbolic space. We also comment on some lattice QCD results when the system is formulated on a curved background modelling the expanding Universe with nonzero $H$.

The talk is based on several recent papers:
1.Ariel Zhitnitsky, "Cosmological Magnetic Field and Dark Energy", Phys. Rev. D 99 (2019) 103518 , e-Print: 1902.07737
2.Ariel Zhitnitsky,``Dynamical de Sitter phase and nontrivial holonomy in strongly coupled gauge theories in an expanding universe,''
Phys. Rev. D 92, 043512 (2015), e-Print: 1505.05151

Speaker: Ariel Zhitnitsky

Zhitnitsky-Coimbra.pdf

73 Kinetic/chemical Equilibration of Heavy DM Particles in Expanding Universe via Langevin equation simulation

Recently, a question about how far chemical freeze-out of heavy Dark
Matter (DM) particles can be pushed down in temperature has been
raised. In this case, kinetic equilibration of heavy DM through
elastic collisions with strongly interacting Standard Model particles
such as quarks and gluons at the temperature of a few GeV could
potentially complicate the consideration. Thus, we study kinetic
equilibration of heavy dark matter particles in non-perturbative
regime using Langevin equation simulation. We note that the kinetic
equilibration of slowly moving DM particle in the thermal bath of SM
particles is analogous to kinetic equilibration of heavy quarks in
Quark-Gluon Plasma and that Langevin equation method is superior
to a standard formulation based on Boltzmann equation because Langevin
simulation allows systematic study even in non-perturbative
regime. As a concrete numerical example, we consider a scalar singlet
DM particle interacting with quarks and gluons and find that the
momentum distribution of DM particle retains the Gaussian form
although the spectrum becomes red-tilted and its overall effect on the
chemical equilibration of DM particles to be {\cal O} (20) %.

Speaker: Prof. Seyong Kim (Sejong University)

skim_xqcd2023.pdf

Parallel session B: 3, Chair: Vivian Incera

74 Color-superconductivity of asymptotically conformal quark matter as a portal between astrophysics and heavy ions collisions

I present a relativistic density functional approach to color superconducting quark matter that mimics quark confinement by a fast growth of the quasiparticle self-energy in the confining region [1]. The approach is shown to be equivalent to a chiral model of quark matter with medium dependent couplings. The approach to the conformal limit at asymptotically high densities is provided by a medium dependence of the vector-isoscalar, vector-isovector and diquark couplings motivated by non-perturbative gluon exchange [2]. While the (pseudo)scalar, vector-isoscalar and vector-isovector sectors of the model are fitted to the mesonic mass spectrum and vacuum phenomenology of QCD, the strength of interaction in the diquark channel is varied in order to obtain the best agreement with the observational constraints from measurements of mass, radius and tidal deformability of neutron stars. These constraints favor an early onset of deconfinement and color superconductivity in neutron stars with masses below one solar mass. I also discuss a new two-zone interpolation scheme for the construction of the hadron-to-quark matter transition [3] that allows to test different structures of the QCD phase diagram with one, two or no critical endpoints in simulations of supernova explosions, neutron star mergers and heavy-ion collisions. I argue that the formation of color-superconducting quark matter drives the trajectories of its evolution in supernovae and neutron star mergers towards the regimes reached in terrestrial experiments with relativistic heavy ion collisions.

[1] O. Ivanytskyi and D. Blaschke, Phys. Rev. D 105, 114042 (2022)
[2] O. Ivanytskyi and D. Blaschke, Particles 5, 514 (2022)
[3] O. Ivanytskyi and D. Blaschke, Eur. Phys. J A. 58, 152 (2022)

Speaker: Oleksii Ivanytskyi (University of Wroclaw, Poland)

XQCD 2023 Ivanytskyi.pdf

75 How baryons appear in low-energy QCD: Domain-wall Skyrmion phase in strong magnetic fields

Low-energy dynamics of QCD can be described by pion degrees of freedom in terms of the chiral perturbation theory (ChPT). A chiral soliton lattice (CSL), an array of solitons, is the ground state due to the chiral anomaly in the presence of a magnetic field larger than a certain critical value at finite density. Here, we show in a model-independent and fully analytic manner (at the leading order of ChPT) that the CSL phase transits to a domain-wall Skyrmion phase when the chemical potential is larger than the critical value $\mu_{\textrm{c}}=16\pi f_{\pi}^2/(3m_{\pi}) \sim 1.03\, \textrm{GeV}$ with the pion’s decay constant $f_{\pi}$ and mass $m_{\pi}$, which can be regarded as the nuclear saturation density. There spontaneously appear stable two-dimensional Skyrmions or lumps on a soliton surface, which can be viewed as three-dimensional Skyrmions carrying even baryon numbers from the bulk despite no Skyrme term. They behave as superconducting rings with persistent currents due to a charged pion condensation, and areas of the rings' interiors are quantized. This phase is in scope of future heavy-ion collider experiments.
This talk is based on arXiv:2304.02940 [hep-ph].

Speaker: Kentaro Nishimura (KEK)

XQCD2023_KentaroNishimura.pdf

Parallel session C: 3, Chair: Wojciech Florkowski

76 Propagation of gauge fields in hot and dense plasmas at higher orders

Thermal field theory is indispensable for describing hot and dense systems. Yet perturbative calculations are often stymied by a host of energy scales, and tend to converge slowly. This means that precise results require the apt use of effective field theories. In this talk I describe how the effective description of slowly varying gauge fields, known as hard thermal loops, can be extended to higher orders. I also discuss how to consistently define asymptotic masses at higher orders; and how to treat spectral functions close to the lightcone.

Speaker: Andreas Ekstedt

HardThermalLoops.pdf

77 Resummation of the soft and hard logarithms in Cold and Dense QCD

We will discuss the recent developments in perturbative QCD at zero temperature and high barionic densities notably how can we effectively resum the so-called soft, hybrid, and hard leading logarithms. We pave the way to the resummation of the next-to-leading logarithms by identifying the anomalous dimensions of the mixed sector in QCD.

By identifying {\em massive} renormalization group (RG) properties within the hard thermal loop (HTL)
formalism, we resum to all orders αpS,p≥3 the leading and next-to-leading logarithmic soft mode contributions to the cold and dense QCD pressure
at high baryon chemical potential μB.
We obtain noticeably reduced residual scale dependence with respect to the state-of-the art results. Extension to the resummation of the so-called hybrid logarithms and hard logarithms is discussed. We finish by paving the way to the evaluation of the anomalous dimensions of the mixed sector, required for the full resummation of the next-to-leading logarithms in QCD.

Mostly based on L. Fernandez and J.-L. Kneur, arXiv:2109.02410 and more recent work in progress with Risto Paatelainen, Saga Säppi, Kaapo Seppänen and Aleksi Vuorinen.

Speaker: Loïc Fernandez (Helsinki Institute of Physics, University of Helsinki)

FernandezXQCD.pdf

16:50 Coffee break

Parallel session A: 4, Chair: Waseem Kamleh

78 Three-gluon vertex in Landau gauge from lattice QCD: planar degeneracy and beyond.

We present an extensive study of the three-gluon vertex in Landau-gauge using quenched lattice-QCD calculations. The main goal of this work is exploring the features of the vertex beyond the well-known symmetric and soft-gluon kinematical configurations, and extend the results for those two kinematics to the general case of three different momenta $q$, $r$ and $p$ are only restricted by the condition $q+r+p=0$ imposed by momentum conservation. We will show how a rational use of Bose symmetry in the choice of the tensors used to develop the transversely projected vertex allows to unveil a quite simple description of the vertex form-factors in the non-perturbative regime of QCD in terms of a single momentum scale formed by the sum of the squares of the three incoming four-momenta $s^2=(q^2+r^2+p^2)/2$. We will evidence as well a clear dominance of the tree-level form factor for any kinematical configuration, something that allows a quite simple description of the vertex in terms of this contribution. The phenomenological implications of these findings will as well be discussed.

Speaker: Dr Feliciano De Soto (Universidad Pablo de Olavide)

deSoto_XQCD19.pdf

79 Higgs-confinement continuity in light of particle-vortex statistics

In gauge theories with fundamental matters, the Higgs and confining regimes are believed to be smoothly connected. This Higgs-confinement continuity forms the foundation of the quark-hadron continuity conjecture, which is a crossover scenario from the nuclear superfluidity phase to the color superconducting phase in dense QCD. Certain superfluid gauge theories, including dense QCD, exhibit nontrivial Aharonov-Bohm (AB) phases around vortices in the Higgs regime. Recently, there has been a growing interest in the question of whether this nontrivial AB phase necessitates a Higgs-confinement transition. In this presentation, I will address this question in favor of Higgs-confinement continuity in relevant gauge-Higgs models. By explicit calculations in lattice models, we demonstrate that the AB phase remains continuous (or even constant when some symmetry constrains the AB phase) across a region bridging Higgs and confining regimes. This finding, in particular, supports the possibility of the quark-hadron continuity. This talk is based on arXiv:2303.02129.

Speaker: Yui Hayashi (YITP, Kyoto University)

xqcd_hayashi.pdf

Parallel session B: 4, Chair: Vivian Incera

80 The sharpness of the quark-hadron transition and the properties of hybrid stars

In this work we propose a new type of hybrid star and study its properties. The quark phase is described by the MIT bag model with repulsive vector interactions and the hadron phase is described by the HLPS model, which is consistent with chiral effective field theory. In the junction of the two phases there can be a discontinuity (a ``jump'') in the energy density, which is related to the latent heat of the strongly interacting matter. We use a prescription to match the two phases, in which we can control the sharpness of the transition. We study how changes in the sharpness affect the mass, radius, tidal deformability and the speed of sound in the star.

Speaker: Dr Fernando Navarra (University of São Paulo, Brazil)

xqcd-navarra.pdf

81 Do hadronic stars and strange quark stars coexist?

In the last years new and exciting data on neutron stars have been obtained by the observations of gravitational waves in merger processes, by the recent X-ray observations of NICER of the closest pulsars, by the multiple band observations of new kind of explosive events, namely the kilonova discovered in 2017. All these data show a (mild) tension among themselves: GW170817 requires a soft equation of state for dense matter, GW190814 might instead indicate that masses up to 2.6M_sun could exist, thus favoring a stiff equation of state. I will discuss a possible scenario that aims to provide a consistent picture of all the experimental and observational information, namely the two-families scenario. This scenario is based on the hypothesis that strange quark matter is absolutely stable. The consequences of this scenario are far reaching: the possible existence of strangelets would provide a significant component of dark matter in the universe.

Speaker: Francesco Di Clemente (University of Ferrara)

hs_qs_coexistence.pdf

Parallel session C: 4, Chair: Wojciech Florkowski

82 Massive thermal loop integrals and bulk viscosity in quark matter

Observations of neutron stars and their mergers have opened a new avenue and motivation for studying QCD matter at very high densities. When studying neutron star mergers in particular, it is vital to understand effects of both the temperature and, for transport quantities such as the bulk viscosity, the quark masses.

Unfortunately, in loop calculations at finite density and/or temperature, taking into account the masses of constituent particles generally leads to analytically intractable and often numerically cumbersome expressions.

By introducing an approximation scheme valid in regions of the phase diagram where a mass $m$ scales numerically with a power of the coupling, $m\propto g^r T$ or $m\propto g^r \mu$, such integrals can be expanded to what is often a much more efficient form, while sacrificing little accuracy.

The approximation has been applied to the thermodynamics of dense pQCD at finite density and temperature with a finite strange quark mass to NNLO, showing excellent agreement with full mass effects.

Moreover, in an ongoing work the scheme is used to study the bulk viscosity, with applications to neutron star mergers in mind. The perturbative values will be combined with results from holographic models, extendable to lower baryon densities, in order to find a prediction for the bulk viscosity valid at densities down to those of realistic merger scenarios

Speaker: Saga Säppi (Technical University of Munich (TUM))

xqcd-masses.pdf

83 Estimating transport coefficients of strongly interacting matter with an extended NJL model

We present some results for transport coefficients in strongly interacting mattter in the light quark sector (up, down and strange) obtained with a novel regularization of the quark polarization functions using an extended version Nambu--Jona-Lasinio model which includes a 't Hooft determinant and eight quark interactions at finite temperature and chemical potential. This new regularization solves some inconsistencies in previously used techniques and has a significant impact in some of the cross-sections which enter into the evaluation of the quarks and antiquarks relaxation times and, as a consequence, in the evaluation of transport coefficients.

Speaker: João Moreira (UBI, CFisUC)

JMoreira_XQCD_2023_v2.pdf

20:00 Conference Dinner

Friday, 28 July

Invited Speaker Session: 3, Chair: Jens Andersen

84 Recent progress in lattice QCD at non-zero temperature and density

I will review the progress in lattice QCD at non-zero temperature and
density, including the calculations
of the equation of state at non-zero baryon density, the nature of the
chiral transition as function of
the quark mass and quantitates related to heavy flavor probes of hot
matter. The latter includes, the
lattice calculation of the heavy quark diffusion constant, heavy quark
potential and quarkonium properties
at high temperatures.

Speaker: Peter Petreczky

xqcd23.pdf

09:45 Coffee break

Plenary session: 3, Chair: Misha Stephanov

85 Quarks in a finite volume and deconfinement as percolation of center-electric fluxes in QCD

In order to understand the puzzle of the free energy of an individual quark in QCD, we explicitly construct ensembles with quark numbers 𝑁𝑉≠0mod3, corresponding to non-zero triality in a finite subvolume 𝑉 on the lattice. We first illustrate the basic idea in an effective Polyakov-loop theory for the heavy-dense limit of QCD, and then extend the construction to full Lattice QCD, where the electric center flux through the surface of 𝑉 has to be fixed at all times to account for Gauss's law. This requires introducing discrete Fourier transfroms over closed center-vortex sheets around the spatial volume 𝑉 between all subsequent time slices, and generalizes the construction of 't Hooft's electric fluxes in the purge gauge theory. Moreover, clusters of the same center-electric fluxes are shown to undergo a percolation phase transition in the effective theory in which we can follow the corresponding Kertesz line through the Z3-crossover region, from the endpoint of the first-order line all the way to the massless limit. The best we can offer to study the same deconfinement phase transition in full QCD, at the moment, is the gauge-invariant definition of clusters of electric flux and their spanning probabilities which appear prohibitively expensive to measure, however.

Speaker: Prof. Lorenz von Smekal (Justus-Liebig University Giessen)

LvS_July2023.pdf

86 Topological structure of the QCD vacuum at finite temperature

The structure of the gluonic vacuum is examined at finite temperature in lattice QCD. The topological charge density on individual Monte Carlo gauge field configurations is calculated, and an algorithm is applied to detect topological objects associated with local extrema. These objects are found to have a distribution of fractional topological charge, and the nature of this distribution changes with the crossing of the critical temperature. Comparisons are made with model predictions, including an instanton-dyon model. The vortex content of these configurations is also studied after fixing to Maximal Centre Gauge. The dominant vortex cluster is observed to "melt" as the temperature crosses into the deconfined phase, causing a collapse in geometry such that centre vortices no longer percolate in all four dimensions.

Speaker: Dr Waseem Kamleh (University of Adelaide)

Kamleh_xqcd2023.pdf

87 Anomalous Electromagnetism in QCD at intermediate baryonic densities

In this talk, the anomalous transport properties of the spatially inhomogeneous phase of dense quark matter known as the Magnetic Dual Chiral Density Wave (MDCDW) phase will be reviewed. I will discuss several anomalous electromagnetic effects that can take place in this phase at low temperatures and intermediate baryonic densities. I will present the axion electrodynamics characterizing this phase. Then, going beyond mean-field approximation, I will show how linearly polarized electromagnetic waves that penetrate the MDCDW medium mix with the phonon fluctuations to give rise to two hybridized modes of propagation called axion polaritons. I will discuss how the formation of axion polaritons in the MDCDW core of a neutron star can add mass to the star via the Primakoff effect, which eventually can trigger the star collapse under the bombardment of gamma-ray bursts. This mechanism can provide a possible solution to the missing pulsar problem in the galactic center.

Speaker: Efrain J Ferrer (The University of Texas at Rio Grande Valley)

XQCD-E J Ferrer.pdf

88 Inhomogeneous meson condensation

The meson condensed phase is an interesting portal on the properties of QCD in a regime in which various methods, including lattice QCD, are reliable.
We discuss inhomogeneous topologically nontrivial configurations of the pion fields
in the framework of chiral perturbation theory.
Solitons characterized by a nonvanishing topological charge naturally emerge. These states that can be identified with baryons surrounded by a bath of pions, meaning that the system has an effective nonvanishing baryonic density.

Speaker: Massimo Mannarelli

massimo_coimbra.pdf

11:55 Best Poster Award

12:05 Lunch

Parallel session A: 5, Chair: Joseph Kapusta

89 Speed of Sound beyond the High-Density Relativistic Limit in Dense Two-Color QCD: Lattice Simulation Results

We obtain the equation of state (EoS) for two-color QCD at low temperature and high density from the lattice Monte Carlo simulation. Two-color QCD is a good toy model of real three-color QCD. The advantage to study this model is that the sign problem is absent even in finite density regime because of the pseudo-reality of quark field. We find that the speed of sound exceeds the relativistic limit (c_s^2/c^2=1/3) after BEC-BCS crossover in the superfluid phase. Such an excess of the sound velocity is previously unknown from any lattice calculations for QCD-like theories. This finding might have a possible relevance to the EoS of neutron star matter revealed by recent measurements of neutron star masses and radii. This talk is based on PTEP 2022 (2022) 11, 111B01 (e-Print: 2207.01253) and its further updates.

Speaker: Etsuko Itou

2023-07-xQCD.pdf

90 QCD thermodynamics with dynamical chiral fermions

We discuss the properties of Quantum Chromodynamics at finite temperature obtained by means of lattice simulations with the overlap fermion discretization. This fermion discretization preserves chiral symmetry even at finite lattice spacing. We present the details of the formulation and discuss the properties of the chiral thermal phase transition. We compare the results obtained with the chiral fermions with predictions by other fermion discretizations.

Speaker: Andrey Kotov

video1.mov

XQCD2023_kotov.pdf

91 Hadron scatterings in small chemical potential

We discuss hadron scatterings in zero temperature and small chemical potential ($\mu$). First, we derive the dispersion relation of a single hadron from the Euclidean-time dependence of the 2-point correlation function. It is found that the energy has linear behavior with respect to $\mu$. We then formulate the HAL QCD method in small $\mu$, where we extract scattering amplitudes via the interaction potentials. It indicates that the amplitude is independent of $\mu$ for any scattering unless the spontaneous breaking occurs. Furthermore, we demonstrate this conclusion by analyzing S-wave scatterings of two pions with isospin $I=2$ and two scalar diquarks in two-color QCD using lattice simulation. The results of the scattering amplitudes in different chemical potentials agree with each other, which is consistent with our conclusion.

Speaker: Kotaro Murakami

MK_HAL_finitemu_final.pdf

92 Exploring external field related phenomena in full lattice QCD

I will summarize the effort of our group to explore new phenomena showing up in external electromagnetic fields in full QCD on the lattice. In particular, I will discuss our effort of studying anomalous transport phenomena such as the chiral separation effect (CSE) as well as the modification of the topological susceptibility in external electromagnetic fields. The latter can be used to extract the contribution of the strong interactions to the axion-photon coupling from first principles. Furthermore, as a proxy for more realistic settings with respect to off-central heavy-ion collisions, we investigate the effects of spatially varying external magnetic fields on the chiral condensate and the Polyakov loop.

Speaker: Bastian Brandt (University of Bielefeld)

talk.pdf

Parallel session B: 5, Chair: Maja Katarzyna Mackowiak-Pawlowska

93 Universal properties of ideal hydrodynamic evolution near the QCD critical point

The hydrodynamic evolution of the quark-gluon plasma (QGP) created in the initial stage of heavy-ion collisions can be approximated by tracking the lines on the QCD phase diagram where the entropy per baryon, s/n, are fixed and conserved at the initial values. The universality of critical phenomena enables us to describe the thermodynamic properties near the QCD critical point using the critical exponents and mapping parameters to the 3D Ising universality class. Our study aims to investigate the universal properties of isentropes near the QCD critical point, specifically focusing on the universal ridge topography of s/n on the phase diagram and its resulting hill shape (local maximum) along the first-order phase transition line on either side of the QGP or hadron phases. We examine the applicability of our model-independent formula to specific examples of the equation of state, including those studied by the Beam-Energy-Scan-Theory (BEST) collaboration.

Speaker: Noriyuki Sogabe

XQCD.pdf

94 Does quark-gluon plasma feature an extended hydrodynamic regime?

In the view that the short wavelength response can be important in small colliding systems and at early-times of a heavy-ion collision, we investigate the response of the near-equilibrium quark-gluon plasma (QGP) to perturbation at non-hydrodynamic gradients. We propose a conceivable scenario under which sound mode continues to dominate the medium response in this regime. Such a scenario has been observed experimentally for various liquids and liquid metals. We further show this extended hydrodynamic regime (EHR) indeed exists for both the weakly-coupled kinetic equation in the relaxation time approximation (RTA) and the strongly-coupled N=4 supersymmetric Yang-Mills (SYM) theory. We construct a simple but nontrivial extension of Müeller-Isareal-Stewart (MIS) theory, namely MIS*, and demonstrate that it describes EHR response for both RTA and SYM theory. Finally, we discuss the possible connection between the extended hydrodynamic regime and observed collectivity in small colliding systems.

Ref: Weiyao Ke and Yi Yin, ArXiv: 2208.01046, Phys.Rev.Lett in press

Speaker: Dr Yi Yin (Institute of modern physics, Chinese Academy of Sciencessti)

EHR_XQCD_YiYin_vFinal.pdf

95 Causality and stability in first-order conformal anisotropic hydrodynamics

My talk focuses on the first-order dissipative anisotropic hydrodynamic theory of a relativistic conformal uncharged fluid, which generalizes Bemfica-Disconzi-Noronha-Kovtun's (BDNK) first-order viscous fluid framework. I explain how the well-known causality problem of Navier-Stokes hydrodynamics of Landau-Lifshitz and Eckart is remedied in the BDNK approach such that the theory also maintains causality in the nonlinear regime with or without general relativity coupling. As a result of outlining the approach, I discuss how causality and stability impose constraints on the behavior of the early-time attractor by applying our newly developed first-order anisotropic theory to the Bjorken flow.

Speaker: Masoud Shokri (Goethe University, ITP)

bdnk_ahydro_talk-2.pdf

96 Centrality Dependence of Multistrange and Strange Antibaryon Production in Heavy-Ion Collisions at High Energies

We consider the experimental data on yields of protons, strange Λ’s, and multistrange baryons (Ξ, Ω), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, and compare them to the results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the Ξ+/Λ, and, in particular, of the Ω+/Λ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.

Speaker: Prof. CARLOS MERINO (Departamento de Física de Partículas, Facultade de Física Instituto Galego de Física de Altas Enerxías (IGFAE) Universidade de Santiago de Compostela - USC)

XQCD2023_CarlosMerino_ParallelSession_B5.pdf

15:40 Coffee break

Plenary session: Closing remarks