A correction to this paper has been published: https://doi.org/10.1007/JHEP11(2024)051

Mexico

Domingo Gallegos

South Korea

Matti Järvinen

France

Eamonn Weitz

Erratum to: Chiral separation effect from holographic QCD

We analyze the dynamics of a first order confinement-deconfinement phase transition in an expanding medium using an effective boundary description fitted to the holographic Witten model. We observe and analyze hot plasma remnants, which do not cool down or nucleate bubbles despite the expansion of the system. The appearance of the hot remnants, the dynamics of their shrinking, and subsequent dissolution and further heating up is very robust and persists in such diverse scenarios as boost-invariant expansion with a flat Minkowski metric and cosmological expansion in a Friedmann-Robertson-Walker spacetime.

Poland

Romuald A. Janik

Israel

Jacob Sonnenschein

Phase Transitions in an Expanding Medium: Hot Remnants

We carry out a detailed analysis of the region slightly outside the conformal window of a non-trivial infrared fixed point in a generic bottom-up holographic setup. We focus on models, which study the dynamics of a scalar field, dual to quark degrees of freedom, in a (nearly) AdS geometry. Such models realize the picture expected for vector-like near-conformal theories from Dyson-Schwinger analysis. The analysis covers a toy model, which allows for analytic solutions, and a more general setup as well, which encompasses a complete model for the ultraviolet physics. We analyze the conditions for the appearance of a parametrically light scalar state in the spectrum, which can act as a candidate for the Pseudo-Nambu-Goldstone boson arising from the breaking of the approximate conformal symmetry. We also present detailed results for the vacuum structure, correlators, and Ward identities in the near-conformal regime.

Jesús Rojas

Deog Hong

Sang Im

Holographic analysis of near-conformal dynamics and light dilaton

Isospin asymmetric nuclear matter is introduced to V-QCD, a bottom-up holographic QCD model. Using a small isospin chemical potential, we extract the symmetry energy in the model, finding excellent agreement with experimental results for some of the potentials. Extending the calculation for finite- and arbitrary-sized isospin chemical potentials, we construct <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>β</mi></mrow></math>-equilibrated neutron stars via the usual Tolman-Oppenheimer-Volkov equations. We find, pleasingly, that the neutron stars passing the mass-radius and tidal deformability constraints are those with the potentials that also lead to excellent symmetry energies.

China

Lorenzo Bartolini

Sven Bjarke Gudnason

Isospin asymmetry and neutron stars in holographic QCD in the Veneziano limit

We investigate fluctuations of hot and dense QCD plasma by using the gauge/gravity duality. To this end, we carry out a comprehensive classification and analysis of quasinormal modes of charged black holes in the holographic V-QCD model. It turns out that the Chern-Simons term determined by the flavor anomalies of QCD is strong enough to drive a modulated instability. While such an instability is expected at high densities, we find that the unstable phase extends to surprisingly low densities and high temperatures, close to the region where data from lattice simulations are available. We also analyze the limit of small temperature which is controlled by a quantum critical <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>AdS</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> point. We study in detail the signatures of the critical point in the quasinormal mode spectrum, focusing on the interplay between the hydrodynamic modes and other modes.

Jesús Cruz Rojas

Tuna Demircik

Modulated instabilities and the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>AdS</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math> point in dense holographic matter

We establish a new tool for studying strongly coupled matter: an effective theory of black holes in gravity, which maps to a hydrodynamic description of field theories via the gauge-gravity duality. Our approach is inspired by previously known effective theories found in the limit of a high number of dimensions. We argue that the new approach can accurately describe phase transitions in a wide class of theories, such as the Yang-Mills and other nearly critical field theories. As an application to a previously unsolved problem, we analyze the interface between confining and deconfining phases in holographic Yang-Mills theory.

Dorin Weissman

Black hole effective theory for strongly interacting matter

We investigate quark-gluon plasma at nonzero density by using two holographic models for QCD based on either brane or Einstein-Maxwell-dilaton actions. We determine the parameters of these models through a systematic statistical fitting procedure to lattice QCD data, which encompasses the equation of state (through the entropy density) and the two lowest baryon number susceptibilities. The predictions from the two models for the higher-order susceptibilities and the equation of state at nonzero density are strikingly similar. In particular, both models suggest the presence of a critical point on the <math><mrow><mo>(</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>,</mo><mi>T</mi><mo>)</mo></mrow></math>-phase diagram near <math><msub><mi>μ</mi><mi>B</mi></msub><mo>/</mo><mi>T</mi><mo>≈</mo><mn>6</mn></math>. The results for the equation of state are in agreement with lattice data for higher-order susceptibilities and experimental data for the cumulants of the net-proton number from the beam energy scan program at the Relativistic Heavy-Ion Collider.

Finland

Niko Jokela

Aleksi Piispa

Refining holographic models of the quark-gluon plasma

We analyze the chiral separation effect (CSE) in QCD by using the gauge/gravity duality. In QCD, this effect arises from a combination of chiral anomalies and the axial U(1) anomaly. Due to the axial gluon anomaly, the value of the CSE conductivity is not determined by the anomalies of QCD but receives radiative corrections, which leads to nontrivial dependence on temperature and density. To analyze this dependence, we use different variants of the V-QCD, a complex holographic model, carefully fitted to QCD data. We find our results for the anomalous CSE conductivity at small chemical potential and nonzero temperature to be in good qualitative agreement with recent results from lattice QCD simulations. We furthermore give predictions for the behavior of the conductivity at finite (vectorial and axial) chemical potentials.

Chiral separation effect from holographic QCD

We study energy-momentum and charge transport in strongly interacting holographic quantum field theories in an anisotropic thermal state by contrasting three different holographic methods to compute transport coefficients: standard holographic calculation of retarded Green’s functions, a method based on the null-focusing equation near horizon and the novel method based on background variations. Employing these methods we compute anisotropic shear and bulk viscosities and conductivities with anisotropy induced externally, for example by an external magnetic field. We show that all three methods yield consistent results. The novel method allows us to read off the transport coefficients from the horizon data and express them in analytic form from which we derive universal relations among them. Furthermore we extend the method based on the null-focusing equation to Gauss-Bonnet theory to compute higher derivative corrections to the aforementioned transport coefficients.

Netherlands

Umut Gürsoy

Ruben Lier

Holographic transport in anisotropic plasmas

Modern hydrodynamic simulations of core-collapse supernovae and neutron-star mergers require knowledge not only of the equilibrium properties of strongly interacting matter, but also of the system’s response to perturbations, encoded in various transport coefficients. Using perturbative and holographic tools, we derive here an improved weak-coupling and a new strong-coupling result for the most important transport coefficient of unpaired quark matter, its bulk viscosity. These results are combined in a simple analytic pocket formula for the quantity that is rooted in perturbative quantum chromodynamics at high densities but takes into account nonperturbative holographic input at neutron-star densities, where the system is strongly coupled. This expression can be used in the modeling of unpaired quark matter at astrophysically relevant temperatures and densities.

Germany

Tyler Gorda

Spain

Carlos Hoyos

Norway

Aleksi Kurkela

Risto Paatelainen

Saga Säppi

Aleksi Vuorinen

Estimate for the Bulk Viscosity of Strongly Coupled Quark Matter Using Perturbative QCD and Holography