Workshop on Holography and Dense Matter 2026

9 sept. 2026, 09:00 → 11 sept. 2026, 18:00 Europe/Paris

APC Laboratory (Paris)

The workshop will focus on applications of the gauge/gravity duality to compact objects and gravitational waves. The purpose is to bring together  researchers  from AdS/CFT, QCD and GR to have an open an informal discussion, point out the interesting open problems and discuss where holography can be useful and how it can interface with other techniques.

Workshop Organizers: Elias Kiritsis, Francesco Nitti, 

SPONSORS

 

mer. 9 septembre

09:00 Welcome Coffee and Registration

1 Quark flavors in holographic QCD and the critical point

give an overview of recent progress in implementing quark flavors and the strange quark mass in the holographic V-QCD model. The model, including its flavor dependence, is pinned down by a detailed comparison with (N_f=2+1) flavor lattice QCD results for the equation of state and quark number susceptibilities at small chemical potentials. Taking into account the flavor dependence and the strange quark mass significantly affects the results at finite density. I discuss implications for neutron star physics and the critical point in the QCD phase diagram as a function of temperature and baryon chemical potential. In beta equilibrium, the critical point is found at much smaller density than in earlier constructions. If one instead imposes constraints mimicking conditions relevant for heavy-ion collisions, the critical point disappears entirely.

Orateur: Matti Jarvinen

10:30 Coffee

2 Near-extremal holographic correlators

Near-extremal black holes with an AdS2 throat are of great interest in
string theory and in holography due to their ubiquity as classical
gravitational saddles. The emergent SL(2,R) symmetry associated to the
throat plays an important role in their low-temperature physics. In this
talk, I will describe recent progress on analytically computing
holographic correlators in black hole spacetimes with a near-extremal
AdS2xR2 near-horizon geometry, focusing on current-current and shear
correlators. By improving on previous matching calculations, I will show
how it is possible to obtain analytical approximations to the
correlators that interpolate between the hydrodynamic (frequencies small
compared to the temperature) and the non-hydrodynamic low-temperature
regimes. The expressions we obtain capture the hydrodynamic poles, the
gapped poles controlled by the SL(2,R) symmetry of the AdS2 throat and
the successive collisions with them. I will also comment on the
appearance of zero temperature gapless poles in the spectrum and their
relation to the SL(2,R) spectrum.

Orateur: Blaise Gouteraux

12:00 Lunch

Street Bida, 1 Rue Nicole-Reine Lepaute, 75013 Paris (arrive by 12.15)

3 Effective and holographic description of fluctuations in first order phase transitions

When fluctuations are suppressed in first order phase transitions, bubble nucleation may be too slow to complete the transition, and the system may explore configurations beyond stable and metastable states. The system can exhibit qualitative differences in thermodynamic and dynamic properties depending on the strength of the coupling, or more precisely, on the number of degrees of freedom involved in the transition. We propose an effective theory coupling a fluid to a scalar order parameter to account for the observed behaviour. The effective theory is a generalization of fluid-scalar models used to describe the dynamics of bubbles in cosmological phase transitions. We test the validity of the effective theory against microscopic results using holography.

Orateur: Carlos Hoyos Badajos

4 Flavor current correlators at finite isospin density: non-Abelian hydrodynamics and quasinormal modes

We study flavor current correlators in strongly coupled matter at finite quark and isospin chemical potentials using holography. Finite isospin density qualitatively modifies the low-energy dynamics of charged currents, combining diffusion with flavor precession. We analyze the corresponding quasinormal-mode spectrum and its interplay with the infrared modes associated with the emergent AdS_2 region of the near-extremal geometry. Finally, we discuss how this structure can be incorporated into an extended hydrodynamic description of the current correlators beyond the conventional hydrodynamic regime.

Orateur: Andrea Olzi

15:40 Coffee

16:10 Discussion

17:30 Wine and Cheese

jeu. 10 septembre

5 Self-sustained, out-of-equilibrium inflation

We use holography to study dS-invariant states of non-conformal, strongly coupled quantum field theories in four-dimensional de Sitter space. We show that out-of-equilibrium effects can sustain exponential inflation within the regime of validity of semiclassical gravity, $H \ll M \ll M_{\text{sp}}$, where $H$ is the Hubble parameter, $M$ is the QFT characteristic scale, $M_{\text{sp}} = M_p / N$ is the species scale, $M_p$ is the Planck scale, and $N^2$ is the number of matter fields. In the holographic description, the required fine-tuning scales only logarithmically with $M_{\text{sp}} / H$, and the resulting solutions feature apparent horizons whose growing area reflects a continuous increase in comoving entropy density. Extending this framework to dynamical gravity, we demonstrate that this inflationary state emerges as the late-time attractor of an initial Friedmann--Lema\^itre--Robertson--Walker universe. Finally, we present preliminary results on a mechanism that terminates this inflationary epoch after a large number of e-foldings.

Orateur: Jorge Casalderrey Solana

09:50 Coffee

6 Gravitational Duals from Equations of State

Orateur: Pau Sole Villaro

7 Non-conformal obstructions to bubble expansion

The hydrodynamics of expanding bubbles plays an important role in the study of gravitational wave emission from first-order phase transitions. It determines the possible expansion types and provides an estimate of the energy available for gravitational wave emission. By interpolating between electroweak- and QCD-like transitions, I will investigate the hydrodynamics of expanding bubbles in transitions with non-conformal thermodynamics. In doing so, I will uncover a new set of obstructions to bubble expansion and a new class of bubble solutions, both of which are absent in electroweak-like transitions, and I will discuss their impact on the space of solutions and the kinetic energy fraction.

Orateur: Mikel Sanchez Garitaonandia

12:00 Lunch

Street Bida, 1 Rue Nicole-Reine Lepaute, 75013 Paris (arrive by 12.15)

8 Dense QCD in Neutron Stars: Twin Stars, Maximum Compactness, and Curvature

I will discuss three recent model-agnostic studies of dense QCD in neutron stars, combining constraints from nuclear theory, perturbative QCD, and multimessenger observations.
First, I will show that twin-star solutions are strongly disfavored by current data. The few surviving cases require highly fine-tuned EOS behavior and do not support the standard interpretation of twin stars as a robust signature of deconfinement. I will then ask how compact a neutron star can be, showing that the maximum-mass star is also the most compact one and that realistic neutron stars satisfy an approximate upper bound of 1/3, determined by perturbative-QCD constraints.
Finally, I will discuss how dense-matter properties are reflected directly in spacetime geometry, including the appearance of negative Ricci curvature and its relation to the trace anomaly.

Orateur: Christian Ecker

9 From pQCD to neutron-star cores: recent advances in equation-of-state inference

I will discuss recent developments in high-order
perturbative QCD calculations at high baryon density. These efforts have
now reached the full next-to-next-to-next-to-leading order (N3LO) for
the pressure of cold and dense QED matter and are approaching the same
order for cold quark matter. The latter result is expected to
substantially improve theoretical control over the high-density regime
of the neutron-star-matter equation of state (EoS), with direct
implications for model-agnostic EoS inference and for the fate of
quark-matter cores inside massive neutron stars.

Orateur: Aleksi Vuorinen

15:40 Coffee

10 Tour de Holography: From c-theorems to spacetime reconstruction

Orateur: Niko Jokela

17:00 Discussion

19:30 Dinner at Auberge Aveyronnaise

ven. 11 septembre

11 Nuclear chiral density wave from field theory and holography

Cold and dense QCD matter may break rotational invariance spontaneously. One anisotropic candidate phase is the chiral density wave, where the chiral condensate oscillates between scalar and pseudoscalar sectors. I will present results from a nucleon-meson model that allows for a chiral phase transition. Taking into account the conditions in the interior of neutron stars and constraints from astrophysical data this model predicts the chiral density wave to be absent from neutron star cores. I will compare these results to a calculation within holography, where the nuclear chiral density wave has been constructed recently for the first time.

Orateur: Andreas Schmitt

09:50 Coffee

12 Bubble Dynamics in Superheated Transitions

First order phase transitions in superheated systems could be
relevant in cosmological contexts and in neutron star mergers. I will
discuss the bubble dynamics in a chiral symmetry restoring superheated
transition in the Witten-Sakai-Sugimoto holographic model. I will show
how to estimate the bubble nucleation rate and the bubble terminal
velocity at zero chemical potential, and conclude with some results
about the finite chemical potential case.

Orateur: Aldo Lorenzo Cotrone

13 Learning quark-gluon plasma properties holographically with neural ODEs

We use neural ODEs and state-of-the-art lattice QCD thermodynamics to calibrate a holographic Einstein-Maxwell-Dilaton model with Gauss-Bonnet corrections. The model quantitatively reproduces the equation of state at zero and finite baryon chemical potential and predicts the phase structure in the T-\mu_B plane, a temperature-dependent, and a peaked, while remaining consistent with thermodynamic constraints.

Orateur: Song He

12:00 Lunch

Street Bida, 1 Rue Nicole-Reine Lepaute, 75013 Paris (arrive by 12.15)

14 Holographic baryons in V-QCD and Tachyon-Chern-Simons action

Chern-Simons terms are necessary to reproduce global flavor anomalies in holographic models of QCD. They are also required to model holographic baryons. We will present how the Chern-Simons action must be generalized in the presence of a bulk tachyon field (dual to the quark bilinear), extending earlier work restricted to flavor-independent quark masses. We will then extend recent work about massless-quarks V-QCD baryons and show that a single baryon compatible with generic quark masses is represented in the gravity dual by a point-like defect. The Tachyon-Chern-Simons action allows us to identify the baryon number with the generalized bulk instanton number. If time permits, we will show that this action produces a Wess-Zumino-Witten term in the boundary effective field theory for the pions and that the baryon current is identified to the boundary Skyrme current.

Orateur: Jean-Loup Raymond

15 Beyond Quasinormal Modes: A Nonlinear Late‑Time Attractor for Black Branes and Viscous Fluids

Orateur: HaoTian Sun

15:40 Coffee

16:10 Discussion

17:00 End