Phase-quenched lattice simulations combined with perturbation theory are an emerging precision approach to determining the thermodynamics of QCD across a wide arc of the phase diagram where the strong coupling constant $\alpha_s$ remains small. In this talk we will introduce this phase-quenched approach to determining QCD's Equation of State (EoS) and argue that at sufficiently high...
In this work, we investigate the combined effects of pressure anisotropy and the inclusion of $\Delta$ resonances on the structural properties of compact stars. The study is performed within a relativistic hadronic framework that incorporates $\Delta$ baryons, where the equation of state (EoS) is constructed under the conditions of charge neutrality and $\beta$-equilibrium.
Pressure...
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 $\rho$...
First-order phase transitions (1st-order PT) have been described in the magnetized Nambu--Jona-Lasinio (NJL) model when the anomalous magnetic moment (AMM) of quarks is included at zero temperature. The AMM quark effect is a consequence of the dynamical chiral symmetry breaking for massive quark in the nonperturbative Quantum Chromodynamics (QCD) regime. The Lattice QCD has described the...
Since Witten's proposal that symmetric deconfined u, d, and s quark matter might be the true absolute ground state, properties of quark stars have been extensively studied. By choosing an equation of state to describe the matter inside these stars, it is possible to solve the Tolman-Oppenheimer-Volkoff equations to obtain the mass and radius of the star. However, it has become clear that...
Dileptons are an important electromagnetic probe of hot and dense QCD matter and are widely regarded as an effective thermometer of heavy-ion collisions. In this work, we investigate dilepton production from an isospin-asymmetric hot and dense quark medium in order to explore the role of isospin imbalance on electromagnetic radiation. We focus in particular on modifications of the dilepton...
We construct an equation of state describing cold and dense matter in the core of neutron stars which includes an admixture of fermionic dark matter and incorporates nucleon effective masses derived from the relativistic Brueckner-Hartree-Fock (BHF) many-body approach within a relativistic mean-field model. Such a BHF-informed mixed-model approach increases stellar compactness, with...
The nuclear equation of state (EoS) of hot and dense matter plays a crucial role in understanding extreme astrophysical phenomena such as proto-neutron stars and binary neutron star (BNS) mergers. In BNS mergers that do not undergo prompt collapse, the post-merger remnant emits gravitational waves (GWs) with characteristic frequencies that encode valuable information about the underlying...
NICER has enabled mass–radius inferences for pulsars using pulse profile modeling (PPM), providing constraints on the equation of state (EOS) of cold, dense matter. To date, PPM and EOS inference have been carried out as two separate steps, with the former using EOS-agnostic priors. This approach has several drawbacks. Ideally, one would perform a fully hierarchical Bayesian inference where...
We investigate the impact of a stiff dark matter equation of state (EoS) on the structure and stability of neutron stars. For dark matter, we use bosonic, self-interacting scalar fields that generate ultra-compact boson stars with compactness exceeding 1/3. Varying the dark matter particle mass and stiffness shifts stellar configurations across distinct regions of the mass–radius diagram,...
The investigation of the composition and evolution of rotating protoneutron stars (PNSs) encodes crucial information about their observable signatures while providing knowledge to advance observational investigations. We study the microphysical and macroscopic evolution of rotating PNSs using a relativistic mean-field model with density-dependent couplings that include finite temperature and...
We develop a family of thermodynamic models for fluid systems based on a virial expansion of the internal energy in terms of the volume density. We prove that the models, formulated for systems with finite number of degrees of freedom $N$, are exactly solvable to any expansion order, as expectation values of physical observables are determined from solutions to nonlinear C-integrable PDEs of...
Isospin-equilibrating weak processes, called ``Urca" processes, are of fundamental importance in astrophysical environments like proto-neutron stars, neutron star mergers, and supernovae. In these environments, matter can reach high temperatures of in the MeV range and be subject to large magnetic fields. Previous studies on the effect of magnetic fields on isospin-equilibration processes...
We revisit the procedure to construct hybrid star EoS introduced in [1] in order to predict sequences of third families of compact stars, based on a non-local chiral quark model equation of state.
The goal of our study is to find a hybrid EoS which maximises the mass defect occurring in the accretion-induced transition from a hadronic star to its hybrid star twin configuration at 1.4...
We explore the changes in the masses of $D$ ($\bar D$) and $B$ ($\bar B$) mesons within isospin asymmetric $\Delta$ resonance matter, utilizing the chiral SU(3) hadronic model extended to the SU(4) and SU(5) sectors, respectively.
In addition to nucleons, the dispersion relations explicitly incorporate the interactions of $D$ and $B$ mesons with decuplet baryons ($\Delta^{++,+,0,-}$).
The...
I will present results from a recent model-agnostic analysis of the neutron-star-matter equation of state (EoS), informed by both ab-initio theoretical limits and astrophysical observations. Allowing for explicit first-order phase transitions, we systematically search for twin-star solutions, i.e. stars of equal mass but differing radii. We find that current constraints exclude all but two...
We constrain the equation of state (EoS) of dense nuclear matter using a relativistic mean-field (RMF) model within a Bayesian inference framework. Constraints from chiral effective field theory ($\chi$-EFT), the observed maximum neutron star mass ($\sim 2 M_\odot$), gravitational-wave data from GW170817, and NICER X-ray mass–radius measurements are combined to obtain posterior distributions...
Anisotropic phases are hypothesised to play a role in the small temperature and large chemical potential regime of the QCD phase diagram, making their existence in the core of neutron stars a concrete possibility. I will present the study of such a phase, the chiral density wave (CDW), defined as an anistropic chiral condensate that breaks spatial invariance. Within a mean-field nucleon-meson...
The microphysical composition of neutron star cores remains an unresolved problem, with current multimessenger data being insufficient to identify the correct description of dense nuclear matter. Quarkyonic matter, where baryons coexist with quarks deep in the Fermi sea, provides a framework which naturally reconciles the issue of massive neutron stars with relatively small radii, made...
Recent astronomical observations now tightly constrain the neutron-star EoS at intermediate densities, where matter may be neither purely hadronic nor weak-coupling quark matter. The favored “stiff” EoS can feature c_s^2 > 1/3 and even a negative (normalized) trace anomaly, challenging normal-phase NNLO pQCD predictions. Based on arXiv:2411.03781, I examine whether this tension can be...
The dynamics of binary neutron star (BNS) mergers are a unique environment to study the state of the matted at extreme conditions. In this context standard matter may undergo a phase transition to the state of deconfined quarks. It has been suggested that such a transition could leave observable imprints in the gravitational waves.
Nevertheless a similar behaviour is also reproduced by...
Neutron stars provide a high-density laboratory to test dark matter (DM) through its gravitational imprint on stellar structure and early evolution. In this talk, I present a unified set of results based on two-fluid modeling of cold neutron stars and evolving proto-neutron stars (PNSs), together with Bayesian model selection, multi-messenger constraints, and inverse parameter inference. For...
We present a unified overview of our recent studies on hybrid neutron stars constrained by NICER observations of PSR J0740+6620 and PSR J0030+0451, and by the low-mass compact object in HESS J1731–347. The hadronic phase is modeled using relativistic mean-field (RMF) equations of state: multiple RMF parameterizations with different interaction schemes are employed for the NICER analysis to...
In this work, we study the effects of ΛΛ-hyperons on neutron star properties employing a metamodel framework for the equation of state (EoS). Different choices for defining the hyperonic couplings with different levels of parametric freedom are discussed. In all models, the predicted NS maximum masses are reduced compared with the purely nucleonic composition as expected. In the case of...
We explore the role of color superconductivity in quarkyonic matter under the conditions of color and electric neutrality at β- and strong equilibrium, as relevant for neutron stars. By explicitly incorporating the color-superconducting pairing gap into the phenomenological model of a smooth transition from hadron to quark matter, we extend the known quarkyonic framework to include this...
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...
The behavior of strongly interacting matter at supranuclear densities and the nature of the associated deconfinement phase transition remain central open problems in nuclear physics and astrophysics. Such extreme conditions are realized in compact stars and related phenomena.
A key uncertainty concerns the energy per baryon of strange quark matter (SQM) relative to that of iron at zero...
The Bodmer-Witten hypothesis proposes that the presence of strange quarks decreases the binding energy of deconfined quark matter, allowing it to stabilize at high densities and favoring its appearance in the cores of compact objects. From this perspective, we investigate the conditions for stellar matter to be composed of strange quark matter. To do so, we employ the equiparticle model [1,...
In the magnetospheres of magnetars, strongly magnetized neutron stars, the magnetic field can be tens of times the critical Schwinger field $B_Q = m^2/e \approx 4.41\cdot 10^{13}$ G. In this strong field regime quantum electrodynamics (QED) becomes nonlinear, which has profound effects on the plasma dynamics of the magnetosphere. Most notably the energies of electrons and positrons become...
We derive a novel BPS bound from chiral perturbation theory minimally coupled to electrodynamics at finite isospin chemical potential. The BPS configurations represent magnetic multi-vortices with quantized flux supported by a superconducting current. The corresponding topological charge density is related to the magnetic flux density, but is screened by the hadronic profile. Such a screening...
Quantum chromodynamics (QCD) at finite baryon chemical potential remains hard to access by first-principles methods, making effective models an essential tool for exploring this region of the phase diagram. The quark–meson (QM) model provides a viable alternative to more established approaches such as the Nambu–Jona-Lasinio model, with the advantage that it can be matched to physical...
We present a comprehensive study of the thermal evolution of isolated neutron stars (NSs) based on a statistical analysis of cooling curves for five purely nucleonic equations of state (EoS). Cooling curves are computed using the publicly available NScool code and statistically compared with X-ray measurements of NS surface luminosities. The predicted luminosity for each source depends on its...
There exist multiple possible phases and microscopic structures of strongly interacting matter at extreme densities. Due to the the non-perturbative nature of QCD and lack of experimental data, there is significant uncertainty in our understanding of dense matter. By combining ground experiments and astronomical observations, we aim to construct a unified theoretical description starting from...
Astrophysical observations, such as neutron star mass–radius measurements inferred from Shapiro delay and X-ray observation of NICER, provide stringent constraints on the electrically neutral equation of state of strongly interacting matter relevant for compact stars. Incorporating heavy-ion collision data, in particular collective flow measurements from the STAR experiment, into the Bayesian...
