arXiv subjects

Claudia Ratti

Publications and source records attributed to Claudia Ratti.

At least 19 recordsLinked to original sources

arXiv2026

Including Thermal Mesons and Meson Resonances in the Chiral Mean-Field Equation of State

The Chiral Mean-Field (CMF) model describes dense matter in terms of baryons and quarks interacting through scalar and vector meson mean fields. In the mean-field approximation, the meson fields are replaced by their expectation values. Their role in generating interactions and in-medium properties is retained, but explicit thermal mesonic excitations are absent. This becomes increasingly problematic at high temperature, where mesons contribute significantly to the thermodynamics of hadronic matter. Here, we keep the original CMF description of dense matter and add the thermal mesonic degrees of freedom using the mesonic sector of the Hadron Resonance Gas (HRG) module in the MUSES framework. Ground-state pseudoscalar and vector mesons account for the missing thermal excitations, while mesonic resonances provide, within the HRG picture, an effective description of mesonic interactions through resonance formation. We study how these contributions affect the pressure, entropy density, energy density, and baryon density, and compare the resulting equation of state with continuum-extrapolated lattice-QCD calculations.

nucl-th↗

arXiv2026

An Extended Chiral Mean-Field Model with Medium-Modified Thermal Mesons for Hot and Dense Hadronic Matter

In this conference proceeding we review an extension of the Chiral Mean Field (CMF) model that consistently incorporates interacting thermal mesons with self-consistent in-medium masses. In this approach, the in-medium masses of pseudoscalar and vector mesons are evaluated through the explicit chiral symmetry-breaking and vector-interaction terms in the Lagrangian respectively, before applying the mean-field approximation. These medium-modified meson properties introduce additional feedback into the CMF equations of motion, leading to a revised equation of state. The impact of this refinement is analyzed by comparing the hadronic model predictions with recent lattice QCD data and other hadronic descriptions, such as the hadron resonance gas model. The modified CMF framework, featuring an improved meson treatment (mCMF),demonstrates enhanced consistency with lattice-QCD results for thermodynamic observables across a broad range of temperatures and baryon chemical potentials.

nucl-th↗

arXiv2026

Updated Hadron List for Transport Simulations of Heavy-Ion Collisions

Hadronic transport approaches used in heavy-ion collision simulations rely on a consistent and accurate hadron list with decay channels. Hadron lists in common use are often experimentally outdated, or, as with the Particle Data Group (PDG) compilations, incompatible with transport codes without further adaptation. We construct PDG2021+, an updated hadron list including all states from the 2021 Particle Data Booklet, together with a binary-decay list designed for direct use in the SMASH transport framework. Using the hadron resonance gas model, we validate the PDG2021+ list against lattice quantum chromodynamics results and experimental yield data. We show that employing $1 \to 2$-body decay chains as a proxy for the full decay processes has a suppressing effect in the low-$p_T$ region of the pion spectrum and introduces a $\sim 3\%$ systematic uncertainty in the pion $\langle p_T \rangle$. Moreover, the inclusion of additional states in PDG2021+ further shifts the pion $\langle p_T \rangle$. These result establish PDG2021+ as a robust, transport-ready hadron list and quantify the systematic effects of decay modeling on key heavy-ion observables.

nucl-th↗

arXiv2026

Strongly coupled quark matter in neutron stars and their mergers

The discovery of the strongly-coupled quark-gluon plasma (sQGP) in high-energy heavy-ion collisions has revealed remarkable properties of matter at high temperature, with transport coefficients close to conjectured bounds from quantum field theory at strong coupling. The high sQGP collision rates imply very large energy uncertainties and the melting of quasiparticle structures. Deploying quantum many-body theory based on the self-consistent $T$-matrix approach for the sQGP at high temperature, we investigate its manifestation at high baryon density and low temperature, as present in neutron stars and their mergers. We constrain the chemical-potential dependence of the quark interaction kernel using first-principles information from Quantum Chromodynamics on baryon-number susceptibilities. Very large collisional widths persist at large density and are found to relegate superconducting phases to rather small temperatures. Instead, a strongly coupled diquark liquid prevails in the thermodynamics under the conditions relevant to neutron-star mergers. At lower densities, the diquarks take over from the single-quark contributions, suggesting a pathway toward hadronization. Our results are consistent with observational constraints on the equation of state of neutron stars, corroborating the presence of strongly coupled quark matter in the interior of these objects.

nucl-th↗

arXiv2026

Thermodynamically Consistent Merging of Multidimensional QCD Equations of State

We present a thermodynamically consistent framework for merging complementary models into a multidimensional QCD equation of state. An internal mixing variable is determined by minimizing a single grand potential at fixed temperature and baryon chemical potential, ensuring thermodynamic consistency and stability. Interactions between the components allow for a crossover, a critical endpoint, and a first-order transition. As a proof of principle, we merge a quantum van der Waals hadron-resonance-gas model with a holographic Einstein--Maxwell--Dilaton model. The resulting equation of state reproduces the appropriate description in each regime, agrees well with available lattice-QCD results, and is suitable for heavy-ion phenomenology over a broad range of temperature and baryon chemical potential.

nucl-th↗

arXiv2026

Deep-learning classification of physically admissible nuclear-matter equations of state

Thermodynamic stability and causality impose fundamental constraints on the equation of state (EoS) of nuclear matter. Verifying these constraints conventionally requires calculating quantities such as the specific heat, baryon-number susceptibility, and speed of sound, which can become computationally expensive when many candidate EoSs must be examined. We investigate whether the normalized pressure surface, $Q(T,μ_B)=P(T,μ_B)/T^4$, alone contains sufficient information to determine the physical admissibility of an EoS. We develop a supervised convolutional neural network (CNN) that uses only this pressure representation to classify EoSs as physically admissible or inadmissible. The network is provided with training labels obtained from direct thermodynmaic stability and causality check and its does not get any information about the parameters of the underlying EoS framework. For EoSs generated within an Ising-mapping framework, the model achieves $97.65%$ accuracy on unseen test data. Applied independently to EoSs from a distinct holographic framework, it achieves perfect classification of the test set. These results show that pressure surfaces contain geometric signatures of thermodynamic stability and causality violations that can be learned directly by a CNN. Because the classifier relies only on the pressure surface, it avoids evaluating higher-order thermodynamic observables during inference and is largely independent of the EoS-generation framework. When the pressure surface is supplied as a two-dimensional array, the machine-learning validation is approximately 20 times faster than direct validation. Our results establish a fast, framework-independent approach for identifying physically admissible EoSs directly from their pressure surfaces.

nucl-th↗

arXiv2026

Lattice-based equation of state with a critical point from constant entropy contours and its comparison to effective QCD approaches

In this work, we systematically assess the performance of a new method from [H. Shah et al., Phys. Rev. C 113, L012201] for locating the QCD critical point using constant-entropy contours by testing it against various effective QCD approaches. We demonstrate that, while the method yields spurious critical points in purely hadronic models (HRG) due to non-parabolic contour behavior at low temperatures ($T \lesssim 120$ MeV), it accurately reproduces the CP location in frameworks that feature a genuine phase transition and benchmarked against lattice QCD, such as Holographic Einstein-Maxwell-Dilaton, and Functional QCD approaches. Building on our previous determination of constant entropy contours using lattice data, we extend that analysis to construct a complete Lattice-based Equation of State (EoS) at finite density, which features a critical point at $(T, μ_B) \approx (114, 602)$ MeV. By integrating the extrapolated entropy density with respect to temperature, we reconstruct the pressure, baryon density, susceptibility, and speed of sound in the critical region, and analyze the focusing behavior of isentropic trajectories in the vicinity of the critical point.

hep-ph↗

arXiv2026

Quark and hybrid stars with renormalization group improvement of NNLO perturbative QCD

Recently, the NNLO perturbative QCD pressure of cold and dense symmetric matter, with arbitrary quark masses, has been resummed within the renormalization-group-optimized perturbation theory (RGOPT) framework. By being imbued with renormalization group properties, the resulting pressure is less sensitive to renormalization scale ($Λ\equiv X μ_B/3$) variations than the NNLO perturbative QCD pressure. Here, we extend this by considering $β$-equilibrium and charge neutrality to evaluate the corresponding equation of state (EoS). We provide a compact ``pocket" fitting formula for the EoS for $N_f=2+1$ massive quarks at different renormalization scale parameter ($X$) values. We describe pure quark stars as well as hybrid stars with quark-cores. Pure quark stars compatible with astrophysical observations were obtained with $X=3.08-3.58$, whereas a larger value (4.10) is needed if the low mass object of the observation GW190814 represents a neutron star. Hybrid stars were built considering three representative hadron models based on a relativistic mean-field description, and chosen to produce soft and stiff EoSs. Stable hybrid stars with masses compatible with the massive pulsar PSR J0740+6620 were obtained considering $X$ of the order of 2 to 2.60-2.98, the largest scale giving rise to hybrid stars with a large quark core with a radius of 5 to 8 km, and the smallest to a small quark core at the center of the star.

nucl-th↗

arXiv2026

QCD critical surface from constant entropy contours

We provide the first mapping of the critical surface in (2+1)-flavor QCD in the full $(T,μ_B,μ_Q,μ_S)$ space, anchored on lattice QCD results at vanishing chemical potentials and obtained within an expansion along contours of constant entropy density. In the pure $μ_B$ direction, this framework yields a critical point at $(T_c,μ_{B,c}) \simeq (114,\, 602)$ MeV. Here we extend the construction to arbitrary directions in the three-dimensional chemical-potential space, parametrized by spherical coordinates $(μ,θ,φ)$, with the radial expansion truncated at $\mathcal{O}(μ^2)$. The resulting two-dimensional surface carries a direction-dependent critical temperature $T_c(θ,φ)$ and baryochemical potential $μ_{B,c}(θ,φ)$, which quantify the shift of the critical point relative to the pure $μ_B$ direction. We find that $μ_{B,c}$ increases by 40-100 MeV along the approximately strangeness neutral direction [$μ_S \approx (0.15$--$0.33)\, μ_B$, $μ_Q \approx 0$] relevant for heavy-ion collisions, while the critical temperature stays essentially unchanged. In the charge-neutral, weak-equilibrium direction~[$μ_Q \approx -(0.05$--$0.1) \,μ_B$, $μ_S = 0$] relevant for neutron star mergers, the critical point, and the associated first-order phase transition, remain present at essentially the same location in the $(T,μ_B)$ plane. We find no evidence for a critical point at large isospin densities, $|μ_Q| / μ_B \gtrsim 1$, relevant for cosmic trajectories in the early Universe, nor along the pure electric-charge or strangeness directions, at least outside the regions where pion or kaon condensation may occur.

nucl-th↗

arXiv2026

Studying the QCD Matter produced in Heavy-Ion Collisions using the MUSES Calculation Engine

The equation of state of hot and dense matter is essential for describing heavy-ion collisions at all collision energies. Here, we explore the capabilities of the latest version of the MUSES Calculation Engine, $\textit{Calliope}$, focusing on software modules and workflows that compute the equation of state and observable properties of the matter produced in heavy-ion collisions. These include several equations of state, ranging from first-principles lattice QCD to phenomenological approaches, with or without a critical point, and with phase-space dimensionality ranging from two dimensions defined by temperature $T$ and baryon chemical potential $μ_B$, to four dimensions after the addition of strangeness and electric-charge chemical potentials $μ_S$ and $μ_Q$. We also discuss modules that provide additional thermodynamic quantities and observables relevant for heavy-ion modeling, including elements of the pressure Hessian matrix and transport coefficients. Workflow examples are constructed that merge two equations of state thermodynamically consistently to extend phase-diagram coverage, and feed the results into an equation of state inverter to produce inputs suitable for hydrodynamic simulations. Finally, we apply this framework to perform a relativistic viscous hydrodynamic simulation with equations of state with an extended $T$ and $μ_B$ coverage and a movable critical point, including effects from transport coefficients that phenomenologically encode critical scaling, at collision energies $\sqrt{s_{NN}}=7.7, 19.6$, and $39$ GeV.

nucl-th↗

arXiv2026

Electric charge fluctuations from lattice QCD in the continuum limit

Electric charge fluctuations $χ_n^Q$ allow comparisons between theory and experiment, but are elusive on the lattice due to severe cutoff effects. We use a 4HEX action to obtain $χ_2^Q$ and, for the first time ever, $χ_4^Q$ in the continuum limit. We find disagreement with the hadron resonance gas (HRG) model, which we cannot explain with finite volume effects. We include light meson interactions in the HRG model via the S-matrix, reducing the tension for $χ_4^Q$, but worsening the agreement for $χ_2^Q$. We propose measuring the ratio $χ_4^Q/χ_2^Q$ at the LHC to investigate this tension.

hep-lat↗

arXiv2026

Partial Pressure Contributions of Hadron Families to the QCD Equation of State

Lattice simulations provide the thermodynamics of quantum chromodynamics (QCD) as a function of the temperature, at zero-to-moderate values of the baryonic chemical potential. However, the contribution of single hadronic species cannot be directly isolated from lattice calculations. In this work, we find linear combinations of up to fourth order susceptibilities which isolate the contribution of hadrons to the QCD pressure according to their baryon number $B$, electric charge $Q$ and strangeness $S$ content. These combinations are valid, provided that the thermodynamics of a strongly-interacting gas in the low-temperature regime can be modeled as a gas of non-interacting hadrons and their resonances. Finally, we test the validity of these linear combinations in the Hadron Resonance Gas (HRG) model and compare them to available lattice QCD results, using continuum-estimated susceptibilities.

hep-ph↗

arXiv2026

Detecting the 3D Ising model phase transition with a ground-state-trained autoencoder

We develop a one-class, deep-learning framework to detect the phase transition and recover critical behavior of the 3D Ising model. A 3D convolutional neural network autoencoder (CAE) is trained on ground-state configurations only, without prior knowledge of the critical temperature, the Hamiltonian, or the order parameter. After training, the model is applied to Monte Carlo configurations across a wide temperature range and different lattice sizes. The mean-square reconstruction error is shown to be sensitive to the transition. Finite-size scaling of the peak location for the reconstruction error susceptibility yields the critical temperature $T_c=4.5128(58)$ and the correlation-length critical exponent $ν=0.63(27)$, consistent with results from the literature. Our results show that a one-class CAE, trained on zero-temperature configurations only, can recover nontrivial critical behavior of the 3D Ising model.

cond-mat.stat-mech↗

arXiv2026

S-wave kaon condensation in neutron-star matter within a chiral model framework with dynamical meson masses

We investigate s-wave kaon condensation in dense matter and neutron stars within the updated Chiral Mean Field model with an improved meson description (mCMF), which incorporates dynamically generated in-medium meson masses arising from explicit chiral symmetry breaking and vector-meson self-interactions. In contrast to conventional relativistic mean-field descriptions with constant meson masses, the mCMF framework introduces a self-consistent feedback between the meson sector and the dense-matter equations of motion. The kaon dispersion relation is derived from the nonlinear SU(3) Lagrangian, including the Weinberg-Tomozawa interaction and additional baryon-pseudoscalar couplings, and the onset of condensation is determined under conditions of charge neutrality and $β$ equilibrium. Our calculations include the full baryon octet together with electrons and muons at zero temperature. We analyze the impact of hyperons, muons, and kaon condensation on the equation of state, on neutron-star mass--radius relations, and neutron-star thermal evolution, and examine the sensitivity of the onset density and stellar properties to variations in the nucleon--kaon scattering length and to different model vector parameters and vector self-interactions. We find that $K^{-}$ condensation sets in between $n \sim (2-8)\, n_0$ (in units of nuclear saturation density) and leads to a moderate to strong softening (in one case, a slight stiffening of the equation of state), depending on the interplay of kaons and hyperons, while remaining compatible with current $2\,M_\odot$ and small-radius neutron-star observational constraints and producing distinguishable behavior in the neutron-star cooling. This work provides an improved and thermodynamically consistent framework for studying exotic degrees of freedom in neutron-star matter.

nucl-th↗

arXiv2026

Uncertainty quantification of holographic transport and energy loss for the hot and baryon-dense QGP

We investigate several transport coefficients across the phase diagram of a holographic Einstein-Maxwell-Dilaton (EMD) model of hot and dense QCD with $N_f=2+1$ flavors. Our results are obtained from an open-source implementation of this model in C++, publicly available as a module within the MUSES Framework. This code includes a new numerical method to extract thermodynamic quantities from near-boundary asymptotics in holographic models, introduced here for the first time, which greatly improves numerical stability and performance in comparison to earlier implementations. Thanks to this improved technique, we are able to compute results for many realizations of our holographic model, sampled from a Bayesian posterior distribution constrained by lattice QCD results at zero chemical potential. This allows us to propagate lattice QCD error bars to predictions of transport coefficients in a wide window of temperature and baryon chemical potential, covering the crossover region, the neighborhood of the predicted critical point, and the line of first-order phase transition. The physical observables include baryon and thermal conductivities, baryon diffusion, shear and bulk viscosities, the jet-quenching parameter, the heavy-quark drag force, and Langevin diffusion coefficients. At vanishing baryon density, we compare our results to estimates extracted by the JETSCAPE Collaboration from heavy-ion data, with which we find good agreement.

nucl-th↗

arXiv2026

Locating the QCD critical point through contours of constant entropy density

We propose a new method to investigate the existence and location of the conjectured high-temperature critical point of strongly interacting matter via contours of constant entropy density. By approximating these lines as a power series in the baryon chemical potential $μ_B$, one can extrapolate them from first-principle results at zero net-baryon density, and use them to locate the QCD critical point, including the associated first-order and spinodal lines. As a proof of principle, we employ currently available continuum-extrapolated first-principle results from the Wuppertal--Budapest collaboration to find a critical point at a temperature and a baryon chemical potential of $T_c = 114.3 \pm 6.9$ MeV and $μ_{B,c} = 602.1 \pm 62.1$ MeV, respectively. We advocate for a more precise determination of the required expansion coefficients via lattice QCD simulations as a means of pinpointing the location of the critical endpoint in the phase diagram of strongly interacting matter.

hep-ph↗

arXiv2026

Chemical potential differentials in the QCD phase diagram from heavy-ion isobar collisions

Temperature and baryon, charge, and strangeness chemical potentials characterize QCD matter under extreme conditions. Differences between these chemical potentials and their ratios probe conserved-charge correlations and the system's response in the multidimensional QCD phase diagram. We extract these quantities from STAR Ru+Ru and Zr+Zr isobar collisions using a Bayesian thermal analysis of hadron yields, which substantially reduces systematic uncertainties, and compare them with Taylor-expanded lattice-QCD and Chiral Mean Field model predictions. Isobar collisions thus emerge as a precision probe of four-dimensional QCD thermodynamics.

nucl-th↗

arXiv2026

Merging multidimensional equations of state of strongly interacting matter via a statistical mixture

We introduce a general method to merge multidimensional equations of state (EoSs) by combining them in a two-fluid equilibrium statistical mixture in the grand canonical ensemble. The merged grand potential density $ω$ is built directly from the input EoSs and the fluid fractions are fixed by minimizing $ω$ at fixed temperature $T$ and baryon chemical potential $μ_B$. Thermodynamic consistency and stability are guaranteed as all thermodynamic quantities are consistently derived from a single merged grand potential $ω(T,μ_B)$ with the correct convexity properties. Our method can accommodate a first-order phase transition and a critical endpoint with mean-field critical exponents. We use this method to merge a van der Waals Hadron-Resonance-Gas EoS with a holographic Einstein-Maxwell-Dilaton EoS that has a critical point and a first-order line. The result is a single EoS, spanning hadronic and deconfined matter over a broad range in $(T,μ_B)$, which can be readily used in heavy-ion hydrodynamic simulations. Our merging method can be generalized to consider a higher dimensional phase diagram (e.g., by considering more chemical potentials) and more than two input EoSs.

nucl-th↗