Name: CSQCD2026
Start: 2026-05-18T09:00:00+02:00
End: 2026-05-23T20:00:00+02:00
Location: Venue

CSQCD2026

from Monday 18 May 2026 (09:00) to Saturday 23 May 2026 (20:00)

Monday 18 May 2026
09:00 Lecture — Introduction to neutron star physics - James Lattimer (Stony Brook University)
Lecture — Introduction to neutron star physics
- James Lattimer (Stony Brook University)
09:00 - 10:15
Neutron stars are the ultimate probe of dense matter physics under cold conditions not achievable in the laboratory. They represent extremes in terms of density, pressure, temperature, magnetic field and spin rate. The lecture will describe the interior structure of neutron stars and establish general limits to their properties from causality, general relativity and nuclear physics. It will also explore how observations of neutron stars in radio, optical, X-ray, gamma-rays and gravitational waves have set constraints that have dramatic implications for nuclear physics.
10:15 Coffee Break
Coffee Break
10:15 - 10:45
10:45 Lecture — Introduction to the Thermal Evolution of neutron stars: Theory and Simulation - Daniele Vigano
Lecture — Introduction to the Thermal Evolution of neutron stars: Theory and Simulation
- Daniele Vigano
10:45 - 12:00
The thermal evolution of neutron stars provides a uniquely sensitive probe of the microphysics of ultra‑dense matter, from nucleonic interactions and superfluidity to the possible emergence of exotic degrees of freedom such as hyperons, deconfined quarks, or dark-sector cooling channels. This lecture will survey the theoretical foundations of neutron‑star cooling, beginning with the structure of the stellar interior, the thermal conductivity and the dominant neutrino‑emission processes that regulate early-time evolution. I will discuss the role of superfluid and superconducting phases, the role of the crust. We will discuss the fundamental role of magnetic‑fields effects, which makes the conductivity anisotropic and enlarge the cooling timescales, making highly magnetised neutron stars X-ray bright and active for longer. I will also present some keynotes on recent state‑of‑the‑art numerical simulations, including modern microphysical inputs, envelope models and magnetic fields. By comparing simulated cooling curves with observations of isolated neutron stars, we will examine current constraints on the equation of state and the composition of dense matter.
12:00 Lecture — Superfluidity in neutron stars - Massimo Mannarelli
Lecture — Superfluidity in neutron stars
- Massimo Mannarelli
12:00 - 13:15
We discuss some properties of superfluids that could be relevant for the evolution of compact stars. Superfluids emerge in many different systems and can be produced and accurately studied in laboratory. We will discuss how some of the results recently obtained in laboratory could be employed to better understand the interior of compact stars. Of particular interest are inhomogeneous superfluid phases, which could emerge within the inner crust of neutron stars and could be emulated employing dipolar ultracold atoms.
13:15 Lunch Break
Lunch Break
13:15 - 15:00
15:00 Lecture — Introduction to thermal field theory - Saga Säppi (Institute of Space Sciences (ICE-CSIC))
Lecture — Introduction to thermal field theory
- Saga Säppi (Institute of Space Sciences (ICE-CSIC))
15:00 - 16:15
A one-hour crash course on QFT at finite density and temperature with the aim to help the students understand basic methods of computing quantities such as the pressure in the finite-density (and also finite-temperature) background necessary for understanding neutron stars (and their collisions), as well as the complications that arise due to the presence of soft scales. Focus on computational tools in the imaginary-time formalism.
16:15 Coffee Break
Coffee Break
16:15 - 16:45
16:45 Lecture --- Dense matter and a hands on section on the MUSES cyberinfrastructure - Mateus Pelicer
Lecture --- Dense matter and a hands on section on the MUSES cyberinfrastructure
- Mateus Pelicer
16:45 - 18:00
This lecture will introduce the basic physics of dense nuclear matter and its role in neutron stars. Emphasis will be placed on the equation of state, matter composition, and thermodynamic properties relevant for astrophysical applications. The lecture will also include a hands-on introduction to the MUSES cyberinfrastructure, where participants will learn how to generate and analyze equation-of-state tables and explore dense-matter models in practice.
Tuesday 19 May 2026
09:00 Neutron Stars as Continuous Gravitational Wave Sources: Status and Perspectives - Ornella Juliana Piccinni (University of the Balearic Islands)
Neutron Stars as Continuous Gravitational Wave Sources: Status and Perspectives
- Ornella Juliana Piccinni (University of the Balearic Islands)
09:00 - 09:50
The detection of gravitational waves has revolutionized astrophysics, offering a novel means to study phenomena that were previously beyond observational reach. This talk will provide a concise overview of current and future gravitational-wave sources, with a specific focus on individual compact remnants, in particular neutron stars formed in core-collapse supernovae and the remnants of binary mergers involving at least one neutron star. I will summarise the main models of gravitational-wave emission expected from these systems, including accreting neutron stars, describing both the standard continuous-wave scenario and the so-called long-transient regime. Recent results will be discussed, highlighting the potential of gravitational-wave measurements to probe the interior structure of these objects and to serve as laboratories for fundamental physics under extreme conditions.
09:50 Continuous gravitational waves from unknown neutron stars in binary systems - Pep Covas Vidal (University of the Balearic Islands)
Continuous gravitational waves from unknown neutron stars in binary systems
- Pep Covas Vidal (University of the Balearic Islands)
09:50 - 10:15
Unknown neutron stars in binary systems might be one of the best sources of continuous gravitational waves (yet to be detected), due to their millisecond rotation rates, the accretion from their companion which can source the required asymmetry, and the vast unexplored parameter space. In this talk we will present the latest search results and will explain which neutron star parameters might be constrained with a future detection.
10:15 The mode-sum approach to dynamical neutron-star tides: The multi-faceted impact of dissipation - SUPROVO GHOSH (University of Southampton)
The mode-sum approach to dynamical neutron-star tides: The multi-faceted impact of dissipation
- SUPROVO GHOSH (University of Southampton)
10:15 - 10:40
Next-generation gravitational-wave detectors are expected to constrain the unknown neutron star equation-of-state from static and dynamical tides in binary neutron star inspirals. Although, the impact of dissipation on the tides are generally considered negligible while modeling the inspiral of binary neutron stars, recent studies shows that fluid dissipation from bulk viscosity of exotic phases(e.g. hyperons and deconfined quark matter) can be significant enough to be detectable using the next generation gravitational wave detectors. As a step towards developing realistic waveform models, we incorporate dissipation from both gravitational radiation reaction and fluid viscosity in the tidal response of a neutron star as a sum of contributions associated with the star’s free oscillation modes. We compute the effective love number incorporating dissipation and the expected ‘tidal lag’ between the induced quadrupole and the external tidal field. We also determine the expected energy loss to heat from fluid dissipation and its impact on the orbital evolution. Finally, based on scaling relations of fluid viscosity with orbital frequency we argue whether fluid dissipation can dominate over gravitational radiation reaction and have detectable impact on the gravitational waveform.
10:40 Coffee Break
Coffee Break
10:40 - 11:10
11:10 Probing the Equation of State and Magnetization of Neutron Star Cores with Superluminous Supernovae - Rachid Ouyed (University of Calgary)
Probing the Equation of State and Magnetization of Neutron Star Cores with Superluminous Supernovae
- Rachid Ouyed (University of Calgary)
11:10 - 11:35
I show that the delayed formation of a hybrid star can account for the unique properties of double-peaked superluminous supernovae (SLSNe). The results indicate that SLSNe can serve as probes of neutron star core physics, offering complementary constraints on the dense-matter equation of state and core magnetization through their light curves and spectra. This framework opens a new avenue for using double-peaked SLSNe to investigate the internal properties of neutron stars.
11:35 Ab initio finite-temperature effects for neutron star binary simulations - Arnau Rios (ICC - UB)
Ab initio finite-temperature effects for neutron star binary simulations
- Arnau Rios (ICC - UB)
11:35 - 12:00
In this talk, I will discuss the predicition of finite temperature effects in dense matter from first principles. I will first discuss a simple, data-driven approach, the virial expansion, which allows for predictions of thermal properties across a wide range of densities and temperatures [1]. I will then discuss extensions to higher density with the Self-Consistent Green's Functions approach [2], possibly discussing superfluid extensions [3]. [1] G. Rivieccio, A. Nadal-Matosas, A. Rios and M. Ruiz,, ApJ 987, 67 (2025). [2] A. Rios, Front. Phys. 8 387 (2020). [3] M. Drissi, A. Rios and C. Barbieri, Ann. Phys. 469, 169730 (2024) & Ann. Phys. 469, 169729 (2024).
12:00 Quasi-Universal Relations for $f$-Mode Oscillations in Compact Stars - Ishfaq Ahmad Rather (ITP, Goethe University)
Quasi-Universal Relations for $f$-Mode Oscillations in Compact Stars
- Ishfaq Ahmad Rather (ITP, Goethe University)
12:00 - 12:25
Gravitational wave astronomy provides a vital tool for probing extreme matter. This study investigates $f$-mode oscillations of cold, catalyzed Neutron stars as well as protoneutron stars with different evolutionary phases. We analyze the collective impact of nucleons, hyperons, phase transition to the quark matter, and dark matter admixtures on these oscillations employing full General Relativistic formalism. The primary focus lies on the quasi-universal relations connecting $f$-modes to bulk stellar properties. Our results demonstrate that these relations remain robust across stars with hyperonic cores, quark matter, and dark matter, as well as in the specific conditions of proto-neutron stars. While the relations exhibit some model dependence, their stability across such diverse physical scenarios highlights their potential for constraining stellar properties from future gravitational wave detections. References: [1] I. A. Rather, K. D. Marquez, P. Thakur, and O. Lourenco, Phys. Rev. D 112, 023013 (2025). [2] P. Thakur, I. A. Rather, and Y. Lim, Phys. Rev. D 112, 043017 (2025). [3] P. Thakur, A. Issifu, I. A. Rather, Y. Lim, and T. Frederico, arXiv:2505.24104 (2025).
12:25 The role of isospin asymmetry in the onset of quark matter - Violetta Sagun (University of Southampton)
The role of isospin asymmetry in the onset of quark matter
- Violetta Sagun (University of Southampton)
12:25 - 12:50
In contrast to symmetric nuclear matter, which has been extensively studied in laboratory experiments, the matter inside neutron stars is highly isospin-asymmetric. We investigate the properties of strongly interacting matter under both symmetric and neutron star-like conditions to determine how electric charge neutrality and beta equilibrium influence the emergence of quark matter. In particular, we establish a relation between the quark onset density in electrically neutral, beta-equilibrated matter and that in symmetric matter. This relation is demonstrated across a broad class of hybrid equations of state and reveals a significant reduction in the quark onset density in highly asymmetric regimes. These findings are further tested through Bayesian analyses of astrophysical measurements, underscoring their relevance for dense matter. A direct consequence of our finding is that a lower-limit constraint on the deconfinement transition in symmetric nuclear matter may imply that this transition could occur in neutron stars at densities even below nuclear saturation density. This study is of significant importance to both the heavy-ion collision and neutron star communities.
12:50 Lunch Break
Lunch Break
12:50 - 14:30
14:30 Binary neutron Star Merger as a Probe of Hadron-Quark Transition - Yongjia Huang
Binary neutron Star Merger as a Probe of Hadron-Quark Transition
- Yongjia Huang
14:30 - 15:20
Multi-messenger observations—from NICER radius measurements and GW170817 tidal constraints to theoretical bounds from chiral EFT and perturbative QCD—have significantly narrowed the space of neutron star equation of state (EOS). These advances increasingly favor a non-monotonic sound speed, hinting at exotic phases like quark matter in massive neutron star cores. However, due to the "masquerade effect," static properties alone struggle to distinguish between a smooth crossover and a sharp phase transition. In this talk, I will discuss how binary neutron star mergers may serve as a dynamical probe of this transition. Using general-relativistic simulations with a quark-hadron crossover EOS, we find that the post-merger remnant is systematically less compact than in purely hadronic models, producing a lower peak gravitational-wave frequency, f2. This signature differs from that in strong first-order phase transitions. Our results suggest that post-merger gravitational-wave signals could help distinguish between different high-density transition scenarios, serving as a complement to static neutron star measurements.
15:20 Relativistic Navier-Stokes for the quark-gluon plasma and neutron star mergers - Yago Bea Besada (Universidad de Vigo)
Relativistic Navier-Stokes for the quark-gluon plasma and neutron star mergers
- Yago Bea Besada (Universidad de Vigo)
15:20 - 15:45
Relativistic theories of dissipative fluids have long been known to suffer from pathologies. In recent years, a novel consistent formulation has been proposed: a well-posed and causal version of the relativistic Navier-Stokes equations. This theory provides a promising alternative to existing approaches and represents a key development in the foundations of relativistic hydrodynamics. We will introduce this emergent framework, motivate its application in addressing state-of-the-art challenges, and present progress in numerical implementations. In particular, we will report on its success in describing experimental data from heavy-ion collisions at the LHC, providing a proof of principle that it offers a viable solution to the causality issues found in current models. We will also discuss ongoing work towards the simulations of viscous neutron star mergers.
15:45 Megahertz Gravitational Waves from Neutron Star Mergers - Jorge Casalderrey Solana
Megahertz Gravitational Waves from Neutron Star Mergers
- Jorge Casalderrey Solana
15:45 - 16:10
Neutron star mergers provide a unique laboratory for the study of strong-field gravity coupled to quantum chromodynamics in extreme conditions. The frequencies and amplitudes of the resulting gravitational waves encode invaluable information about the merger. Simulations to date have shown that these frequencies lie in the kilohertz range. They have also shown that, if quantum chromodynamics possesses a first-order phase transition at high baryon density, then this is likely to be accessed during the merger dynamics. Here, we show that this would result in the nucleation of superheated and/or supercompressed bubbles whose subsequent dynamics would produce gravitational waves in the megahertz range. We estimate the amplitude of this signal and compare it to the sensitivity of planned future detectors.
16:10 Probing the Finite-Temperature Neutron Star Equation of State with Post-Merger Gravitational Waves - Bhaskar Biswas (Hamburg University)
Probing the Finite-Temperature Neutron Star Equation of State with Post-Merger Gravitational Waves
- Bhaskar Biswas (Hamburg University)
16:10 - 16:35
The post-merger phase of binary neutron star (BNS) mergers provides a unique opportunity to probe the equation of state (EOS) of dense matter at finite temperatures and out-of-equilibrium conditions. While current EOS constraints are dominated by cold inspiral signals, the hot and turbulent post-merger remnant encodes additional microphysics that remains unexplored. In this talk, I will present results from full general-relativistic smoothed particle hydrodynamics simulations with SPHINCS_BSSN, implementing parametric models of the thermal EOS. I will show how variations in the thermal sector subtly but detectably alter the post-merger gravitational-wave spectrum and late-time thermal profiles. These effects, potentially observable with third-generation detectors such as Cosmic Explorer and Einstein Telescope, open a new window into constraining dense matter physics beyond the cold EOS.
16:35 Coffee Break
Coffee Break
16:35 - 17:05
17:05 Recurring regions for neutron-star observables - Alexander Clevinger (Kent State University)
Recurring regions for neutron-star observables
- Alexander Clevinger (Kent State University)
17:05 - 17:30
I will report on a novel, somewhat analytical way to produce equations of state (EOSs) that generate particular values of neutron star mass, radius, and tidal deformability. This is possible because our description for the EoS of dense matter can produce recurring regions, small areas where several EoSs cross in the mass-radius and mass-tidal deformability diagrams. We can place recurring regions in desired locations of these diagrams, corresponding e.g., to a given observation. Our prescription is versatile, in the sense that different microscopic models can be used for the low density hadronic phase and high density quark phase, as long as they are connected by a percolation, a description that mimics quark deconfinement and is motivated by QCD. The several EoSs that pass by a recurring region can present different thresholds for the boundaries of the percolation region (different beginning and ending for the quark deconfinement region), as well as different orders for the phase transition at the boundaries. When combining all these features, our prescription allows one not only to produce an EoS that matches an observation, but also one that matches specific chosen criteria for the EoS. The EoSs produced by this new method will be specially suitable for the study of dense-matter properties in future gravitational-wave observations, when both the inspiral and post-merger phase signals will become available. Our numerical code that calculates recurring regions using CompOSE microscopic EoSs is open source and publicly available
17:30 Measure the moment of inertia and ellipticity of neutron stars with gravitational waves - Zhiqiang Miao
Measure the moment of inertia and ellipticity of neutron stars with gravitational waves
- Zhiqiang Miao
17:30 - 17:55
We identify a previously unrecognized spin–orbit resonance that can naturally arise in neutron star binaries. This resonance provides a new and direct probe of neutron star ellipticity, enabled by finite stellar quadrupole moments such as those produced by strong internal magnetic fields. We show that the resonance produces a distinctive and measurable gravitational-wave phase shift, allowing precise measurement of the neutron star’s ellipticity and moment of inertia. We further conduct the first ellipticity search across the entire gravitational-wave catalog up to O4a, finding no detections but establishing the framework for future constraints. We demonstrate that detecting this resonance would have significant implications for both astrophysics and fundamental physics, including the internal structure of neutron stars, the prevalence of magnetars in binaries, and tests of strong-field gravity.
17:55 Can all the observed neutron stars contain color-superconducting quark cores? - Oleksii Ivanytskyi (University of Wroclaw)
Can all the observed neutron stars contain color-superconducting quark cores?
- Oleksii Ivanytskyi (University of Wroclaw)
17:55 - 18:20
The possibility of quark deconfinement in the interiors of neutron stars is investigated within the physics-informed Bayesian analysis of the observational data on neutron stars, which allows for distinguishing between the scenarios with quark cores and without them [1]. For this the recently proposed three-flavor nonlocal NJL model of quark matter with the scalar attractive, vector repulsive and diquark pairing interaction channels is used to construct a large set of asymptotically conformal hybrid quark-hadron equations of state with CFL color superconductivity [2]. Independent of the analyzed set of observational data the most probable hybrid equations of state are statistically preferred over the purely hadronic baseline on the level of one-two orders of magnitude. This suggests that quark cores may exist in all observed neutron stars with the most probable onset density below 1.5 saturation densities and the onset mass well below one solar mass. Such small values are explained using a simple model of quark confinement, which shows that the onset density of deconfinement strongly depends on isospin asymmetry: in symmetric matter it is at least three times larger than in neutron stars [3]. This answers the question why in neutron stars deconfinement occurs at rather small densities, while under the conditions of heavy ion collisions its traces are not reliably detected up to the highest densities of the proton flow data of Denielewicz et al. [4]. [1] A. Ayriyan, O. Ivanytskyi, D. Blaschke, arXiv:2509.02554 [nucl-th] (2025). [2] O. Ivanytskyi, Phys.Rev.D 111, 3 (2025). [3] P. Panasiuk, O. Ivanytskyi, V. Sagun, D. Blaschke, A. Ayriyan, inpreparation (2026). [4] P. Danielewicz, R. Lacey and W. G. Lynch, Science 298, 1593 (2002).
Wednesday 20 May 2026
09:00 First-order phase transitions in neutron stars - Mark Alford (Washington University in St. Louis)
First-order phase transitions in neutron stars
- Mark Alford (Washington University in St. Louis)
09:00 - 09:50
It has long been hypothesized that above nucleaer density there might be a first-order transition from dense nuclear matter to quark matter, and hence that sufficiently heavy neutron stars might have quark matter cores. I will discuss some of the observable signatures of such a transition, including features of the mass radius relation and of the dynamics of neutron star mergers.
09:50 The case for very massive neutron stars - Jorge Ernesto Horvath (IAG-USP, Brazil)
The case for very massive neutron stars
- Jorge Ernesto Horvath (IAG-USP, Brazil)
09:50 - 10:15
The quest for the maximum mass possibly achieved by a neutron star (NS) is an old venerable subject. 50+ years ago very low values were considered, mainly put forward from a theoretical point of view. The discovery of the binary pulsar PSR 1913+16, and later on, similar systems, allowed the determination of the mass with two or more decimal places, leading to the (now proved wrong) idea of a “canonical” value of $1.4 M_{\odot}$. However, progressively higher values were reported and confirmed. Today the consensus is that at least $2 M_{\odot}$ neutron star exist. Higher values are not only possible, but actually published by many authors. We shall discuss in this presentation how the existing sample of 104 measured NS masses leads to infer a maximum mass of $\sim 2.5-2.6 M_{\odot}$, using Bayesian techniques with an without a cutoff (related to the very end of a theoretical sequence), and a few important individual cases which may indicate that the maximum mass may be well above the $2.2 M_{\odot}$ ballpark generally accepted. These cases include PSR J0952-0607, PSR J1748-2021B in NGC 6440, 4U 1820-30 and the GW events in which enigmatic low-mass members have been seen.
10:15 Bayesian Inference of Neutron Star EOS from Future High-Precision Measurements of Their Radii - Bao-An Li (East Texas A&M University)
Bayesian Inference of Neutron Star EOS from Future High-Precision Measurements of Their Radii
- Bao-An Li (East Texas A&M University)
10:15 - 10:40
To more precisely constrain the Equation of State (EOS) of supradense neutron-rich nuclear matter, future high-precision X-ray and gravitational wave observatories are proposed to measure the radii of neutron stars (NSs) with an accuracy better than about 0.1 km. However, it remains unclear which aspects of the EOS will be better constrained and by how much. In this talk, we address this issue based on our recent work [1,2,3] within a Bayesian framework using a meta-model EOS for NSs. In particular, we infer the posterior probability distributions (PDFs) of incompressibility and skewness of symmetric nuclear matter, as well as the slope, curvature, and skewness characterizing the density dependence of the nuclear symmetry energy, from high-precision mock radius data with accuracies ranging from about 1.0 km to 0.1 km. Effects of high-precision NS radius measurements on determining properties of the first-order hadron-quark phase transition and the formation of twin stars will also be discussed. References [1] Bayesian Inference of Hybrid Star Properties from Future High-Precision Measurements of Their Radii, Bao-An Li, Xavier Grundler, Wen-Jie Xie and Nai-Bo Zhang, ArXiV: 2505.00194, *The Astrophysical Journal (2026) in press.* [2] Bayesian quantification of observability and equation of state of twin stars, Xavier Grundler and Bao-An Li, *Phys. Rev. D 112 (2025) 10, 103012* [3] Bayesian inference of fine features of the nuclear equation of state from future neutron star radius measurements to 0.1 km accuracy, Bao-An Li, Xavier Grundler, Wen-Jie Xie and Nai-Bo Zhang, *Phys. Rev. D 110 (2024) 10, 103040*
10:40 Coffee Break
Coffee Break
10:40 - 11:10
11:10 Pion condensation in QCD. From chiral perturbation theory to weak coupling - Jens Oluf Andersen (NTNU)
Pion condensation in QCD. From chiral perturbation theory to weak coupling
- Jens Oluf Andersen (NTNU)
11:10 - 11:35
In QCD at nonzero isospin chemical potential and zero baryon chemical potential, the Dirac determinant is manifestly real and the system does not suffer from the sign problem. Consequently, one can perform lattice simulations and study pion condensation non-perturbatively. For this reason, pion condensation is an ideal test bed for low-energy models and theories. In this talk, I will discuss chiral perturbation theory and the quark-meson model at finite isospin and zero baryon number. I compute the pion condensate, the quark condensate, and the speed of sound. The results are compared with lattice simulation over a large range of values for mu_I as well as weak-coupling calculations at large density. Our results are generally in good agreement.
11:35 Rotational effects in quark stars: comparing different models - Adamu Issifu (Instituto Tecnologico de Aeronautica)
Rotational effects in quark stars: comparing different models
- Adamu Issifu (Instituto Tecnologico de Aeronautica)
11:35 - 12:00
This work presents the rotational properties of self-bound quark stars within general relativity using two representative quark matter equations of state: the vector MIT bag model and the density-dependent quark mass model. Uniformly rotating equilibrium sequences are constructed to explore their mass--radius relations, moments of inertia, quadrupole moments, surface redshifts, Keplerian frequencies, and rotational energy components. A key outcome of this work is a detailed decomposition of the stellar energy budget, explicitly separating gravitational, internal, rotational, and binding energy contributions in rotating quark stars. We find that rotation accentuates intrinsic differences between the equations of state: the MIT model supports more massive configurations ($M_{\max}\gtrsim 3.3\,M_\odot$) with larger moments of inertia and reduced deformability, whereas the DDQM model yields stars with larger radii that reach the mass-shedding limit at lower spin frequencies. We show that combined measurements of mass, radius, and spin frequency can break degeneracies between quark matter models, with massive, rapidly rotating pulsars favoring MIT-like equations of state, while larger radii in canonical-mass stars point to DDQM-like behavior. These rotational observables, increasingly accessible through \textit{NICER} observations and next-generation gravitational-wave detectors, provide a promising avenue to test the existence and properties of self-bound quark matter in compact stars.
12:00 Speed of Sound in Neutron Stars: Thermodynamic Structure and Implications for Dense Matter - Gargi Chaudhuri (Physics Group, Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700064, India)
Speed of Sound in Neutron Stars: Thermodynamic Structure and Implications for Dense Matter
- Gargi Chaudhuri (Physics Group, Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700064, India)
12:00 - 12:25
Compact stars provide unique astrophysical laboratories for exploring the properties of dense nuclear matter. Observations of pulsars, together with recent gravitational-wave detections, have placed stringent constraints on the nuclear equation of state (EOS). Among various thermodynamic quantities, the speed of sound plays a central role in understanding the structure of neutron star and the behavior of matter at supranuclear densities. In this work, we present a detailed investigation of the thermodynamic structure of the speed of sound and its decomposition in dense matter. We demonstrate that the curvature term of the speed of sound undergoes a sign change in purely hadronic EOSs, even in the absence of a phase transition or the system reaching the conformal limit. This behavior is directly connected to the maximum of the first derivative of the energy per particle. We further analyze the behavior of the trace anomaly and the polytropic index within the relativistic mean-field (RMF) framework, showing that the sign of the trace anomaly at high densities is sensitive to whether the EOS is stiff or soft. We also investigate hadron–quark phase transitions using both Maxwell and Gibbs constructions and apply the speed-of-sound decomposition scheme to these scenarios. In particular, we explore the behavior of the average speed of sound in purely hadronic stars, quark stars, and hybrid stars, identifying characteristic signatures associated with the presence of a phase transition. Finally, we extend our analysis to finite-temperature phase transitions, highlighting their impact on the thermodynamic properties of dense matter.
12:25 Neutron Star Properties and Femtoscopic Constraints - Isaac Vidaña (INFN, Sezione di Catania)
Neutron Star Properties and Femtoscopic Constraints
- Isaac Vidaña (INFN, Sezione di Catania)
12:25 - 12:50
We construct the equation of state of hypernuclear matter and study the structure of neutron stars employing a chiral hyperon-nucleon interaction of the Julich–Bonn group tuned to femtoscopic ¨ Λp data of the ALICE Collaboration, and ΛΛ and ΞN interactions determined from lattice QCD calculations by the HAL QCD Collaboration that reproduce the femtoscopic ΛΛ and Ξ − p data. We employ the ab-initio microscopic Brueckner–Hartree–Fock theory extended to the strange baryon sector. A special focus is put on the uncertainties of the hyperon interactions and how they are effectively propagated to the composition, equation of state, mass-radius relation and tidal deformability of neutron stars. To such end, we consider the uncertainty due to the experimental error of the femtoscopic Λp data used to fix the chiral hyperon-nucleon interaction and the theoretical uncertainty, estimated from the residual cut-off dependence of this interaction. We find that the final maximum mass of a neutron star with hyperons is in the range 1.3 − 1.4 M⊙, in agreement with previous works. The hyperon puzzle, therefore, remains still an open issue if only two-body hyperon-nucleon and hyperon-hyperon interactions are considered. Predictions for the tidal deformability of neutron stars with hyperons are found to be in agreement with the observational constraints from the gravitational wave event GW170817 in the mass range 1.1 − 1.3 M⊙.
12:50 Lunch Break
Lunch Break
12:50 - 14:30
14:30 Problems with using linear sigma models in QCD - Robert Pisarski (brookhaven national laboratory)
Problems with using linear sigma models in QCD
- Robert Pisarski (brookhaven national laboratory)
14:30 - 15:20
Usually an effective model can be used at low energy, as long as it incorporates the relevant global symmetries, and the appropriate spectrum. Recently, however, it has been understood that the anomaly structure at large distance has to match that at short distances, known as the 't Hooft anomaly. I outline how for two flavors, a standard linear sigma model satisfies the 't Hooft anomaly, while that for three flavors does not.
15:20 QCD correction to the non-leptonic rate in dense Quark Matter - Hanna Lempiäinen (University of Helsinki)
QCD correction to the non-leptonic rate in dense Quark Matter
- Hanna Lempiäinen (University of Helsinki)
15:20 - 15:45
The bulk viscosity of dense quark matter (QM) plays a central role in the dynamics of neutron star mergers by controlling the dissipation of density oscillations. In the neutrino-transparent regime at low temperatures, this transport coefficient is governed by the non-leptonic weak process u + d ⇆ u + s, whose microscopic rate enters directly into the QM bulk-viscosity coefficient. Despite its importance, existing perturbative calculations of this rate are only known to leading order. In this talk, we present preliminary results for the leading O(α_s) QCD correction to the non-leptonic weak reaction rate, computed using real-time Kadanoff–Baym formalism in the low-temperature, high-density regime. The QCD correction is gauge invariant and fully ultraviolet- and infrared-finite, with all soft and collinear divergences cancelling between real and virtual contributions. Consequently, Kinoshita–Lee–Nauenberg–type infrared cancellations occur at this perturbative order for the weak flavour-changing process in dense QCD.
15:45 Compact stars with QCD phase transition: transport and oscillations - Armen Sedrakian (University of Wroclaw and FIAS)
Compact stars with QCD phase transition: transport and oscillations
- Armen Sedrakian (University of Wroclaw and FIAS)
15:45 - 16:10
I will discuss two aspects of compact stars with strong phase transitions. The first topic covers the structure and transport in the quark phases of compact stars, while the second deals with oscillation modes, boundary conditions at the interface between quark and hadronic phases, and the resulting oscillation modes.
16:10 Impossible Twin Stars - How can we see phase transitions? - Jan-Erik Christian
Impossible Twin Stars - How can we see phase transitions?
- Jan-Erik Christian
16:10 - 16:35
We discuss the possibility of a first-order phase transition from hadronic matter to deconfined quark matter under various circumstances. The hadronic part is described by a relativistic mean field equation of state, which enables us to span a wide net of scenarios while still employing a microphysically motivated setup. In order to examine the full parameter space, we use multiple approaches of increasing sophistication for the quark phase. We place a particular focus on the detectability of phase transitions through current and future observations, like mass, radius, and gravitational wave events. One of the clearest signals for a phase transition is twin stars, where two neutron stars with the same mass feature very different radii. However, recent data disfavors this scenario, increasing the difficulty of conclusively detecting the presence of quark matter in neutron stars. Despite this, radius constraints such as the NICER measurement of J0614 may point towards the existence of hybrid stars in a less definite fashion.
16:35 Finite Energy Sum Rules in Dense Nuclear Matter - Cristian Villavicencio (Universidad del Bio-Bio)
Finite Energy Sum Rules in Dense Nuclear Matter
- Cristian Villavicencio (Universidad del Bio-Bio)
16:35 - 17:00
We present an analysis based on Finite Energy Sum Rules (FESR) formulated in a general in-medium framework. This approach allows us to investigate the in-medium evolution of parameters in both the nonperturbative sector of QCD and the hadronic sector. We discuss the methodology, emphasizing its advantages as well as its main challenges and limitations. As specific high-density applications, we examine the density dependence of the nuclear decay constant and the QCD vacuum structure associated with the nuclear lasagna phase, whose description is based on skyrmionic models.
17:00 Cold quark matter from multi-loop techniques - Maximilian Delto (CERN)
Cold quark matter from multi-loop techniques
- Maximilian Delto (CERN)
17:00 - 17:25
An accurate theoretical description of pressure of cold and dense quark matter is a key ingredient for constraining models of the equation of state of neutron stars at large baryon density. While soft-gluon logarithmic corrections at third order in the strong coupling constant have been obtained recently, the corresponding hard contribution has so far only been evaluated partially. In this talk, we present a new approach to this outstanding challenge. Using well-established cutting rules, we relate vacuum Feynman integrals at finite baryon chemical potential to on-shell integrals over lower-loop amplitudes at zero chemical potential. In this formulation, the chemical potential solely acts as an upper cut-off on the energy of the on-shell phase space. We explain how the computation of constrained phase-space integrals can be streamlined using methods widely employed in the study of vacuum scattering amplitudes, such as integration-by-parts reduction and differential equations, and illustrate our setup with examples at different loop orders and for both massive and massless quarks.
17:25 Poster Session
Poster Session
17:25 - 19:25
Contributions

18:05 Equation of state of hot and dense matter and implication on Gravitational Wave from Binary Neutron Star post-merger - Nilaksha Barman (Inter-University Centre for Astronomy and Astrophysics)

18:25 Superconducting multi-vortices at finite isosption chemical potential in chiral perturbation theory - Marcela Lagos Flores (Universidad San Sebastián)

19:05 Probing Hybrid Stars with NICER and HESS J1731–347 Using the Speed of Sound Model - Suman Pal (Physics Group, Variable Energy Cyclotron Centre, 1/AF Bidhan Nagar, Kolkata 700064, India)

19:05 Integrable statistical models and QCD phase diagrams - Xin An (Ghent University)

19:05 Strong-field quantum electrodynamics in magnetar magnetospheres - Olavi Kiuru (University of Helsinki)

19:05 The Quark-Meson diquark model as an effective model for neutron stars equation of state. - Mathias Pavely Nødtvedt (Norwegian University of Science and Technology (NTNU))

19:05 Observable Signatures of a Quarkyonic Phase in Neutron Stars - Probit Jyoti Kalita (National Institute of Technology Rourkela, Rourkela, India)

19:05 Pairing-gap corrections to speed of sound and trace anomaly in 2SC matter and QCD-like superfluid matter - Shuhei MINATO (The University of Tokyo)

19:05 Dilepton Production as a Probe of Pion Condensation in Hot and Dense QCD Matter - Aritra Bandyopadhyay

19:05 Hybrid star with the NJL model using a density-dependent vector coupling - Rafael Cardoso (Federal University of Santa Catarina and University of Coimbra)

19:05 Medium modifications of heavy-light mesons in hot and dense resonance matter - Manpreet Kaur (Dr. B R Ambedkar National Institute of Technology Jalandhar (144008), Punjab, India)

19:05 Thermal Evolution of Isolated Neutron Stars: Constraints on the EoS and Pairing Gaps - Afonso Ávila (University of Coimbra)

19:05 Equation-of-state-informed pulse profile modeling - Mariska Hoogkamer (University of Amsterdam)

19:05 Nuclear chiral density wave in neutron stars? - Orestis Papadopoulos (University of Southampton)

19:05 Isospin equilibration and Bulk Viscous Dissipation in Neutron Star Megers: Effects of magnetic field - Pranjal Tambe (Inter-University Centre for Astronomy and Astrophysics)

19:05 Effects of a Brueckner-Hartree-Fock–corrected effective mass on speed of sound, conformality, and observables of dark matter–admixed neutron stars - Arijit Das (Indian Institute of Science Education and Research Thiruvananthapuram)

19:05 Mass Defect in Accretion Induced Phase Transitions to the Third Family of Compact Stars - Dhrubajyoti Rakshit (Faculty of Physics and Astronomy, University of Wrocław)

19:05 Parametrised phase transition to quark matter in binary neutron star merger - Giuseppe Rivieccio (Universitat de Valencia)

19:05 Quarkyonic Matter with Color Superconductivity: Implications for Compact Stars - Christoph Gärtlein

19:05 General-relativistic simulations of binary strange star mergers - Yong Gao (Gao)

19:05 A new approach to determine the thermodynamics of deconfined matter to high accuracy - Leon Sandbote (University of Helsinki)

19:05 Generating ultra-compact hybrid stars with bosonic dark matter - Sarah Louisa Pitz (Goethe University Frankfurt am Main)

19:05 Strange quark matter formation in compact stars: nucleation, metastability, and astrophysical implications - Mirco Guerrini (University of Ferrara and INFN Ferrara)

19:05 Hyperons and Δ's in rotating protoneutron stars: Local properties - Franciele Manoel da Silva (University of Tübingen and Universidade Federal de Santa Catarina)

19:05 Anisotropic Compact Stars in the Presence of $\Delta$ Resonances - Priyanshi . (Dr. B R Ambedkar National Institute of Technology, Jalandhar, Punjab, India)

19:05 Proto-Neutron Stars with Color Superconductivity - Selina Kunkel

19:05 Model-independent constraints for twin-star solutions - Sofia Blomqvist (University of Helsinki)

19:05 Probing Dark Matter from Cold Neutron Stars to Proto-Neutron Stars Using Two-Fluid Modeling, Bayesian Evidence, and Machine-Learning Inference - Prashant Thakur (Yonsei University)

19:05 Uniting STAR Flow Inference with Astrophysical Data - Pavlo Panasiuk (University of Coimbra)

19:05 How many states of matter are we missing? Ask neutron stars. - Eva Lope Oter (Universidad Complutense de Madrid)

19:24 The impact of the Si/O interface on core-collapse supernova explosions - Nicolas Houry (CEA)
Thursday 21 May 2026
09:00 QCD phase structure at high baryon density - Mei Huang
QCD phase structure at high baryon density
- Mei Huang
09:00 - 09:50
I will give a brief introduction on QCD phase structure at high baryon density,including the status of the critical end point (CEP), the existence of long-lived false vacuum in dynamical first-order phase transition and its contribution to compact stars, as well as dense matter under magnetic filed and rotation.
09:50 Masquerading Hybrid Stars with Dark Matter: Early Quark Matter Onset and Exotic Configurations - Carline Biesdorf (Instituto Tecnológico de Aeronáutica (ITA))
Masquerading Hybrid Stars with Dark Matter: Early Quark Matter Onset and Exotic Configurations
- Carline Biesdorf (Instituto Tecnológico de Aeronáutica (ITA))
09:50 - 10:15
Dark matter can strongly influence the internal structure of compact stars, reshaping the conditions for quark matter formation. In this work, we investigate its role in hybrid stars - objects that contain both hadronic and quark matter phases. Using a two-fluid approach, where normal matter and dark matter interact only through gravity, we demonstrate that dark matter raises the central pressure of neutron stars and triggers the onset of quark matter at unexpectedly low stellar masses. This effect gives rise to *masquerading hybrid stars*, whose mass-radius relations closely resemble those of purely hadronic stars, complicating observational identification. We also describe a new class of objects, *dark oysters*, with extended dark matter halos and compact cores. These findings highlight the diverse structural possibilities of compact stars influenced by dark matter and emphasize the need to account for dark matter effects in astrophysical observations. Our results open new avenues for constraining dark matter properties through neutron star phenomenology and gravitational-wave astronomy.
10:15 Dark matter effects on the properties of hybrid and twin stars - Harish Chandra Das
Dark matter effects on the properties of hybrid and twin stars
- Harish Chandra Das
10:15 - 10:40
We investigate the influence of dark matter (DM) on the structure and stability of hybrid and twin stars within a two-fluid framework in which DM interacts with baryonic matter purely through gravity. The baryonic sector is described using relativistic mean-field theory for nucleonic matter and a constant sound-speed parametrization for quark matter, while the DM component is modeled as self-interacting fermions. We find that the presence of DM suppresses the emergence of hybrid and twin star branches compared with DM-free configurations. The degree of suppression depends sensitively on the phase-transition pressure and the energy-density discontinuity for fixed sound speed, as well as on the DM particle mass and fractional abundance. Stars featuring DM-dominated cores or halos are governed primarily by DM properties, whereas the emergence of twin or hybrid configurations re- mains controlled by the quark-matter equation of state. Incorporating current observational constraints further narrows the allowed parameter space for twin stars in both scenarios.
10:40 Coffee Break
Coffee Break
10:40 - 11:10
11:10 Dark Matter and Neutron Stars - Michel HG Tytgat (Université Libre de Bruxelles)
Dark Matter and Neutron Stars
- Michel HG Tytgat (Université Libre de Bruxelles)
11:10 - 11:35
Neutron stars provide unique laboratories for probing the physics of dark matter. I begin by reviewing the scenario proposed by Goldman and Nussinov, in which dark matter accumulates inside neutron stars and can trigger their collapse into solar-mass black holes. In this picture, dark matter cores form seed black holes that consume their host stars, producing solar-mass black holes beyond the expectations of standard stellar evolution. Such events may generate distinctive gravitational-wave signals, offering a probe of dark matter and a possible alternative to primordial black holes. I then focus on asymmetric fermionic dark matter. After outlining model-building challenges, I show how self-interactions can reduce the Chandrasekhar mass required for collapse. I briefly discuss the phase structure of interacting fermionic dark matter at finite density and its implications for the equation of state. Finally, I consider scenarios with extra spatial dimensions, which enhance this instability and strengthen constraints on dark matter properties, particularly their mass.
11:35 Dual Approach to Quarkyonic Matter at Finite Temperature - Dyana Duarte (Universidade Federal de Santa Maria)
Dual Approach to Quarkyonic Matter at Finite Temperature
- Dyana Duarte (Universidade Federal de Santa Maria)
11:35 - 12:00
We present a field-theoretical description of quarkyonic matter in which quark–nucleon duality is implemented through ghost fields that compensate the extra nucleonic degrees of freedom. The framework reduces to a nucleon effective field theory at low density and describes the dynamical formation of a nucleon shell near the Fermi surface as baryon density increases. A phenomenological equation of state for the high-density matter is proposed, and a first extension of the model to finite temperature is outlined.
12:00 Color superconductivity, proto-neutron stars and dark matter in compact stars - Jürgen Schaffner-Bielich (Goethe University Frankfurt)
Color superconductivity, proto-neutron stars and dark matter in compact stars
- Jürgen Schaffner-Bielich (Goethe University Frankfurt)
12:00 - 12:50
The physics and astrophysics of compact stars experiences major advancements in quite diverse research areas opening up new directions for future investigations. Here, we report on recent extensions of compact star physics as the inclusion of color superconducting phases in neutron stars, the implications for proto-neutron star evolution, and the properties of compact stars with self-interacting dark matter. The results will be confronted with modern constraints on the mass and radius of neutron stars from the NICER X-ray mission, and recent claims for extremely compact neutron star configurations.
12:50 Excursion & Conference Dinner
Excursion & Conference Dinner
12:50 - 22:00
Friday 22 May 2026
09:00 From pQCD to neutron-star cores: recent advances in equation-of-state inference - Aleksi Vuorinen (University of Helsinki)
From pQCD to neutron-star cores: recent advances in equation-of-state inference
- Aleksi Vuorinen (University of Helsinki)
09:00 - 09:50
I will discuss recent developments in perturbative QCD at high baryon density, focusing on work towards completing the next-to-next-to-next-to-leading order pressure of cold quark matter. This 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. In parallel, I will present recent results on the impact of first-order phase transitions on EoS inference, demonstrating that so-called twin-star solutions are currently on the verge of being ruled out.
09:50 A More Natural Method to Infer the EOS from Neutron Star Observations - James Lattimer (Stony Brook University)
A More Natural Method to Infer the EOS from Neutron Star Observations
- James Lattimer (Stony Brook University)
09:50 - 10:15
Traditional Bayesian methods for inferring neutron star properties from observations begin by parameterizing equation of state (pressure-energy density) space in order to generate mass-radius information. These methods contain uncertainties from their arbitrary choices of equation of state models and their parameters. Those uncertainties are at least as large as the observational uncertainties. We develop an alternative strategy by directly parameterizing mass-radius space instead of pressure-energy density space, and then using a precision analytical method for inverting mass-radius relations into their underlying equations of state.
10:15 Nonequilibrium dynamics in the inner crust of a neutron star - Daniel Pęcak (Institute of Physics of the Polish Academy of Sciences)
Nonequilibrium dynamics in the inner crust of a neutron star
- Daniel Pęcak (Institute of Physics of the Polish Academy of Sciences)
10:15 - 10:40
Astronomical observations of neutron stars provide data on the kilometer scale, while the nuclear interaction, fundamental for neutron stars, operates on the femtometer scale. To describe physical processes across so many orders of magnitude, one needs effective models. The inner crust of a neutron star is a complex system, where a lattice of nuclei strongly interacts with superfluid neutrons. One can neglect neutron and proton degrees of freedom and capture the essential physical phenomena by parametrizing nuclei with their effective mass, which emerges from the interaction with the background neutrons. We developed the WBSk Toolkit [1], a general-purpose tool that uses time-dependent density functional theory to perform simulations of the inner crust without geometric constraints. We use generalized Skyrme nuclear energy-density functionals of the Brussels-Montreal family. We study the nonequilibrium dynamics of a nucleus in different layers of the neutron star, which allows us to calculate the effective mass. Moreover, we identify, above a threshold velocity, three distinct mechanisms of energy dissipation: phonon emission, Cooper pair breaking, and vortex ring creation. The last mechanism is particularly interesting in the context of a microscopic source of glitches. [1] D. Pęcak, A. Zdanowicz, N. Chamel, P. Magierski, G. Wlazłowski Physical Review X 14, 041054 (2024)
10:40 Coffee Break
Coffee Break
10:40 - 11:10
11:10 Application to neutron stars of Relativistic Mean-Field predictions and QCD Equation of State from effective Lagrangians - Luca Passarella (Politecnico di Torino and INFN)
Application to neutron stars of Relativistic Mean-Field predictions and QCD Equation of State from effective Lagrangians
- Luca Passarella (Politecnico di Torino and INFN)
11:10 - 11:35
We aim to construct a unified Equation of State (EOS) capable of describing strongly interacting matter over a wide range of densities and temperatures. As a first step, we validate a Bayesian framework to rigorously incorporate astrophysical constraints into the cold, dense matter sector by considering Relativistic Mean-Field (RMF) models based on the exchange of $\sigma, \omega$, and $\rho$ mesons, including nonlinear nucleon-$\sigma$ couplings and density-dependent $\rho$ coupling. A large set of models is generated using a Markov chain Monte Carlo approach within a Bayesian framework to reproduce nuclear physics knowledge encoded in terms of the nuclear empirical parameters and $\chi$EFT predictions for low-density neutron matter. These models are then filtered, using astrophysical constraints, such as the tidal deformability obtained from GW170817 parameter estimation and the observational masses deduced from radioastronomy. We obtain a set of selected RMF models compatible with present nuclear and astrophysical constraints, finding that RMF models can produce EOS soft enough to predict low values for neutron star radii compatible with GW170817, and can be made stiff enough at larger densities to be compatible with NICER analyses of massive neutron stars, reaching maximum mass values of up to $2.6M_\odot$. To extend this description to finite temperatures and deconfinement, we develop a theoretical framework based on an effective Lagrangian where a dilaton field encodes the breaking of scale symmetry in QCD. Starting from the pure gauge $SU(3)_c$ sector, the low-temperature gluon condensate is dominated by the dilaton, evaporating into quasi-free gluons above the critical temperature. To address thermal effects, we study the role of dilaton fluctuations, finding a first-order phase transition, as expected from the results of lattice QCD. We extend this framework by including mesons ($\sigma$, $\pi$, $\omega$, $\rho$) and nucleons along with their thermal fluctuations, at finite temperature and chemical potential. This effective Lagrangian, incorporating both broken-scale symmetry and explicit chiral symmetry breaking, allows us to explore the QCD phase diagram over a wide range of temperatures and densities using a single EOS.
11:35 Hyperons and neutron star mergers - Hristijan Kochankovski (University of Barcelona)
Hyperons and neutron star mergers
- Hristijan Kochankovski (University of Barcelona)
11:35 - 12:00
This study investigates how hyperons influence neutron star mergers using a large sample of equations of state. Our systematic analysis reveals that the presence of thermal hyperons induces a characteristic increase (several percent) in the dominant post-merger gravitational wave frequency. Additionally, the presence of hypernuclear matter leads to lower average temperatures and higher maximum densities during the post-merger phase. We also quantify the impact of strangeness on the threshold mass for collapse and ejected mass. These findings provide benchmarks for identifying strangeness in ultra-dense, hot matter through future multi-messenger observations.
12:00 Color superconductivity under neutron-star conditions at next-to-leading order - Tyler Gorda (The Ohio State University)
Color superconductivity under neutron-star conditions at next-to-leading order
- Tyler Gorda (The Ohio State University)
12:00 - 12:25
The equation of state of deconfined strongly interacting matter at high densities remains an open question, with effects from quark pairing in the preferred color-flavor-locked (CFL) ground state possibly playing an important role. Recent studies suggest that at least large pairing gaps in the CFL phase are incompatible with current astrophysical observations of neutron stars. At the same time, it has recently been shown that in two-flavor quark matter, subleading corrections from pairing effects can be much larger than would be naively expected, even for comparatively small gaps. Here, I present next-to-leading-order corrections to the pressure of quark matter in the CFL phase arising from the gap and the strong coupling constant, incorporating neutron-star equilibrium conditions and current state-of-the-art perturbative QCD results. The corrections are again quite sizable, and they allow one to constrain the CFL gap in the quark energy spectrum to $\Delta_{\rm CFL} \lesssim 140~{\rm MeV}$ at a baryon chemical potential $\mu_{\rm B} = 2.6~{\rm GeV}$, even when allowing for a wide range of possible behaviors for the dependence of the gap on the chemical potential.
12:25 Peaks of the Speed of Sound in Dense QCD Matter - Ricardo Luciano Sonego Farias (Federal University of Santa Maria)
Peaks of the Speed of Sound in Dense QCD Matter
- Ricardo Luciano Sonego Farias (Federal University of Santa Maria)
12:25 - 12:50
The violation of the conformal limit for the speed of sound, $c_s^2=1/3$, has emerged as a critical feature of dense strongly interacting matter. Astrophysical observations — including gravitational-wave data from LIGO/Virgo and precise neutron-star radius measurements from NICER — indicate that the equation of state must undergo a rapid stiffening at intermediate baryon densities. This behavior is commonly associated with the emergence of a peak in the speed of sound and may signal the onset of a phase transition in the dense QCD regime. Direct lattice QCD simulations at finite baryon density are severely hindered by the sign problem. Nevertheless, effective QCD models, as well as lattice-accessible theories such as two-color QCD and QCD at finite isospin chemical potential, provide valuable insight into the nonperturbative dynamics of dense quark matter. These approaches consistently support the existence of a peak in $c_s^2$, in qualitative agreement with astrophysical expectations. We present and analyze recent analytical and numerical results obtained within effective models of QCD, with particular emphasis on the behavior of the equation of state and its stiffening at intermediate densities. These results help establish a concrete connection between effective theoretical descriptions of dense QCD matter and phenomenological constraints derived from astrophysical observations.
12:50 Lunch Break
Lunch Break
12:50 - 14:30
14:30 Describing baryonic matter with relativistic mean field models constrained by Bayesian inference - Constança Providência (University of Coimbra)
Describing baryonic matter with relativistic mean field models constrained by Bayesian inference
- Constança Providência (University of Coimbra)
14:30 - 15:20
The composition of the core of neutron stars is still under debate. Agnostic descriptions of the equation of state are a powerful tool to determine the allowed region in the pressure-energy density or mass-radius space defined by observations and theoretical ab-initio calculations. These methods, however, cannot really give information on the neutron star composition. Understanding the microphysics that spans the regions determined by agnostic descriptions is, therefore, necessary. In particular, we are interested in identifying signatures of the onset of exotic degrees of freedom or quark matter. It is expected that the next generation of gravitational wave and electromagnetic detectors will allow the determination of the neutron star radius and mass with a small uncertainty, which will have an important impact on the information that can be extracted about the high density equation of state of baryonic matter. Microscopic models are used to describe the different phases of matter, including relativistic mean field models, chiral symmetric models, and quark models. Given a set of constraints, Bayesian inference will be used to determine the model parameters. As constraints , we consider nuclear matter properties, neutron star observations and theoretical ab-initio calculations at low and high density. The dependence on the priors, on the constraints and on the choice of the likelihoods will be discussed. Within these microscopic models, the properties of neutron stars and nuclear matter are discussed taking into account the constraints that have been imposed. The effect of considering different compositions of matter will also be discussed.
15:20 First-principles motivated priors for neutron-star equation-of-state inference via constrained Brownain bridges - Oleg Komoltsev (Goethe-Universität Frankfurt am Main)
First-principles motivated priors for neutron-star equation-of-state inference via constrained Brownain bridges
- Oleg Komoltsev (Goethe-Universität Frankfurt am Main)
15:20 - 15:45
As our understanding of cold, extremely dense matter grows, a multidisciplinary approach that combines recent progress in multimessenger neutron-star observations with theoretical knowledge of the equation of state (EoS) becomes increasingly essential. In this talk, I present a new physically motivated framework for encoding prior knowledge about dense matter arising from chiral effective field theory and perturbative quantum chromodynamics. The new method generates model-agnostic, nonparametric priors for neutron-star EoS inference that are stable, causal, and thermodynamically consistent by construction. It generalizes Gaussian processes and is based on constructing constrained Brownian bridges, whose correlation properties can be tuned at will, allowing flexibility between conservative priors and theory-informed priors. Unlike existing nonparametric approaches, it does not rely on shooting procedures, intermediate likelihoods, or ad hoc switching between EoS representations.
15:45 Equation of State at finite temperature in the era of new nuclear physics and multimessenger constraints - Chiranjib Mondal (Universite Libre de Bruxelles)
Equation of State at finite temperature in the era of new nuclear physics and multimessenger constraints
- Chiranjib Mondal (Universite Libre de Bruxelles)
15:45 - 16:10
In this contribution, I will start with an overview of different types of equation of state modelling in the Bayesian formalism, to demonstrate the িmpact of different experimental and observational constraints. Further, I will present equations of state at finite temperature obtained with Brussels-Skyrme-on-a-Grid (BSkG) energy density functionals developed at Brussels, which are unified across the crust and core of the neutron star environment. These models have demonstrated remarkable accuracy over the whole nuclear chart on the masses, and fission barriers of nuclei, but at the same time they also satisfy recent astrophysical constraints. I will also outline the impact of our calculations at finite temperatures on the composition of the crust in the neutron stars. Our next goal is to apply these equations of state in the end-to-end simulation of binary neutron star mergers.
16:10 Neutrino dynamics in neutron star mergers - Liam Brodie (Washington University in St. Louis)
Neutrino dynamics in neutron star mergers
- Liam Brodie (Washington University in St. Louis)
16:10 - 16:35
Neutron star mergers create environments of hot, ultra-dense matter where the strong interaction governs the behavior but cannot be solved exactly or perturbatively using current methods. These collisions throw matter out of equilibrium and provide a unique laboratory to explore the phases and properties of dense matter. Simulations of neutron star mergers let us follow this matter in detail and link it to signals we can actually observe, like gravitational waves. Capturing the relevant physics in merger simulations is key to reducing uncertainties in what we infer from these signals. I will focus on the role of neutrinos in merger environments. I will show how assumptions about the local neutrino population influence weak interactions and thereby impact the equation of state and the gravitational wave signal. I will also present first results on a comparison of neutrino distributions from a Monte Carlo neutrino scheme, which are not necessarily in thermal equilibrium, with Fermi-Dirac (thermally equilibrated) distributions. I will show the impact on the average energy, average absorption opacity, and net rate of neutrino/antineutrino absorption.
16:35 Coffee Break
Coffee Break
16:35 - 17:05
17:05 Spin-polarized quark matter and its phase diagram - William Tavares (Rio de Janeiro State University)
Spin-polarized quark matter and its phase diagram
- William Tavares (Rio de Janeiro State University)
17:05 - 17:30
Spin polarization in nuclear matter has been recognized as a key ingredient in the description of highly vortical systems formed in heavy-ion collisions, motivating detailed studies of the associated phase structure under extreme conditions. Recently, a spin potential, $\mu_{\Sigma}$, has been proposed in the context of lattice quantum chromodynamics (LQCD) as a quantity that measures the tendency of quark spins to align along a preferred direction. Within LQCD, this concept has been explored in setups without gluonic degrees of freedom and is interpreted as a new thermodynamic quantity, allowing its straightforward implementation in effective quark models and facilitating direct comparisons with lattice results. In this work, we study the effects of spin polarization within the two-flavor entangled Polyakov--Nambu--Jona-Lasinio (EPNJL) model at finite temperature, using the mean-field approximation. We find that the effective quark masses decrease as a function of the spin potential, an effect that is further enhanced by increasing temperature. The resulting phase diagram in the $T \times \mu_{\Sigma}$ plane exhibits a crossover at sufficiently low spin potential and high temperatures, which is separated from first-order phase transition lines at higher spin potentials by a critical endpoint. Our results are in qualitative agreement with recent LQCD findings and predictions from renormalizable models.
17:30 RG resummed equation of state for quark matter: applications to compact stars. - Jean-Loic Kneur (Lab Charles Coulomb, Montpellier, France)
RG resummed equation of state for quark matter: applications to compact stars.
- Jean-Loic Kneur (Lab Charles Coulomb, Montpellier, France)
17:30 - 17:55
We consider the renormalization group optimized perturbation theory (RGOPT) at next-to-next-to-leading order (NNLO) to evaluate the equation of state (EoS) for cold quark matter, incorporating full strange quark mass dependence. RGOPT entails an all-order RG resummation that generically reduces the renormalization scale uncertainties as compared to perturbative QCD (pQCD). We obtain mass-radius relations for pure quark stars and compare results with pQCD predictions. We also consider more general EoS for hybrid stars, with our approach implemented for the quark matter contribution.
17:55 Constraining nonperturbative gluon mass by the neutron star observations - David Alvarez Castillo (Institute of Nuclear Physics PAS)
Constraining nonperturbative gluon mass by the neutron star observations
- David Alvarez Castillo (Institute of Nuclear Physics PAS)
17:55 - 18:20
In this work we present hybrid stars with a superconducting quark matter core covered by a hyperonic nuclear matter. The deconfined phase is modelled within a chirally symmetric density functional approach and follows a first order phase transition via a Maxwell construction from a hyperonic DD2 equation of state. While the hadronic phase is fixed, the range of properties of the quark matter phase as well as the position of quark onset is the result of the variation of three physical parameters of the microscopic quark Lagrangian, the vector and diquark couplings as well as the non-perturbative gluon mass. The latter represents the scale at which quark interactions cease and quark matter becomes asymptotically conformal. An earlier proposed fit formula for the quark equation is generalized to the case of arbitrary nonperturbative gluon mass and is used to produce a large set of hybrid equations of state applied for Bayesian analysis of the observational data on neutron stars supplemented by the experimental data on the vector meson mass. The analysis allows us not only to obtain the most probable values of the quark Lagrangian, but also suggest a constraint on the nonperturbative gluon mass. ‎
18:20 Closing Remarks
Closing Remarks
18:20 - 18:30
Saturday 23 May 2026

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