arXiv subjects

Stefano Burrello

Publications and source records attributed to Stefano Burrello.

12 recordsLinked to original sources

arXiv2026

Light clusters in warm magnetized stellar matter: equation of state and thermodynamic response

Finite-temperature equations of state (EOSs) with a controlled treatment of composition-dependent effects are becoming increasingly important for modeling proto-neutron stars and binary neutron star merger remnants, where warm matter may coexist with strong magnetic fields. At sub-saturation densities, light nuclear clusters may also emerge with sizeable abundances. For beta-equilibrated matter, with or without neutrino trapping, an interplay between magnetic fields and light-cluster formation naturally arises in determining the matter composition: charge neutrality and weak equilibrium transmit the effects of Landau quantization to the baryonic sector, modifying the equilibrium charge content; at the same time, light-cluster formation also favors the increase of the proton fraction by binding protons into nuclear clusters. In this work, we investigate this interplay within a generalized relativistic mean-field framework, in which light clusters up to alpha particles are included as explicit degrees of freedom and their in-medium dissolution is described through phenomenological binding-energy shifts. We show that the formation and subsequent dissolution of light clusters, combined with magnetic-field effects, leave characteristic signatures in the matter pressure, the isothermal squared speed of sound, and the heat capacity, leading to significant modifications of the thermodynamic stiffness of the EOS and of the heat-storage properties of warm stellar matter. Furthermore, we investigate the impact of the isovector terms of the EOS, namely its symmetry energy, on these features. These results provide microscopic insights relevant to modeling the hydrodynamic and thermal evolution of proto-neutron stars and neutron star merger remnants, while establishing a baseline for the development of more comprehensive finite-temperature EOSs for compact-star applications.

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arXiv2026

Spinodal instability in nuclear matter with light cluster degrees of freedom

We investigate the thermodynamical stability of low-density isospin-symmetric nuclear matter at finite temperature, explicitly including light clusters as degrees of freedom. Within a generalized mean-field framework, we compute the curvature matrix of the free-energy density and determine the spinodal region, identifying the conditions under which mechanically unstable modes may develop in the presence of clustering. Particular attention is devoted to the formal consequences of introducing an infrared momentum cutoff in the density and current moments, which effectively accounts for Pauli-blocking effects and the associated reduction of low-momentum quasiparticle states in the medium. We show that when the cutoff is density dependent, thermodynamic consistency requires additional contributions to the chemical potentials and extra terms also appear in the first hydrodynamic moment, influencing both the stability analysis and the location of the spinodal boundary. We further examine the character of the unstable modes and find that a sufficiently stiff density dependence of the cutoff may drive clusters to fluctuate out of phase with nucleons, pushing them toward low-density regions while nucleonic instabilities grow, in contrast with the in-phase pattern obtained when in-medium effects are neglected. Our results shed new light on the role of light clusters in the phase dynamics of warm, dilute nuclear matter, with implications for heavy-ion collisions and for the physics of neutron-star crusts.

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arXiv2025

ESO Expanding Horizon White Paper: Revealing the properties of matter at supranuclear densities with gravitational waves

Understanding dense matter under extreme conditions is one of the most fundamental puzzles in modern physics. Complex interactions give rise to emergent, collective phenomena. While nuclear experiments and Earth - based colliders provide valuable insights, much of the quantum chromodynamics phase diagram at high density and low temperature remains accessible only through astrophysical observations of neutron stars, neutron star mergers, and stellar collapse. Astronomical observations thus offer a direct window to the physics on subatomic scales with gravitational waves presenting an especially clean channel. Next-generation gravitational - wave observatories, such as the Einstein Telescope, would serve as unparalleled instruments to transform our understanding of neutron star matter. They will enable the detection of up to tens of thousands of binary neutron star and neutron star - black hole mergers per year, a dramatic increase over the few events accessible with current detectors. They will provide an unprecedented precision in probing cold, dense matter during the binary inspiral, exceeding by at least an order of magnitude what current facilities can achieve. Moreover, these observatories will allow us to explore uncharted regimes of dense matter at finite temperatures produced in a subset of neutron star mergers, areas that remain entirely inaccessible to current instruments. Together with multimessenger observations, these measurements will significantly deepen our knowledge of dense nuclear matter.

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arXiv2025

Phase-space excluded-volume approach for light clusters in nuclear medium

A phase-space excluded-volume approach is developed to investigate the in-medium properties of light clusters in nuclear matter. In this approach, light clusters can exist only if the total nucleon phase-space occupation of the surrounding nuclear medium -- including explicit contributions from light clusters -- is sufficiently low. The distribution functions of nucleons and light clusters are determined self-consistently by accounting for the interplay between in-medium effects and thermodynamic properties. By employing standard Skyrme energy-density functionals to model the nuclear mean-field potential, the approach enables the evaluation of the Mott momentum and the fraction of light clusters in nuclear matter. Furthermore, it can be readily integrated into dynamical models, to study in-medium effects on light clusters, based on measured yields in heavy-ion collisions.

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arXiv2024

Probing nuclear structure and the equation of state through pre-equilibrium dipole emission in charge-asymmetric reactions

We investigate the pre-equilibrium dipole response in the charge-asymmetric reaction $^{40}$Ca+$^{152}$Sm, of recent experimental interest, at several beam energies within the range $[5, 11]$ AMeV and different collision centralities. By employing Skyrme-like effective interactions for the nuclear mean field, we probe the role of the different ingredients performing theoretical calculations based on the time-dependent Hartree-Fock approach or a semi-classical transport model that also includes two-body correlations. A comparative analysis between these approaches allowed us to disentangle the role of deformation effects in the entrance channel from the ones associated with structure details of genuine quantal nature on the dipole emission. Moreover, we also investigate the impact of the occurrence of residual two-body collisions on the reaction dynamics. This study contributes to the understanding of the microscopic processes that determine the complex dynamics of low-energy heavy-ion collisions along the fusion-fission path, which is relevant to super-heavy element synthesis, unraveling interesting connections with the characteristics of the nuclear effective interaction and the associated equation of state.

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arXiv2024

Dynamics of dilute nuclear matter with light clusters and in-medium effects

We investigate the dynamics of dilute systems composed of nucleons and light clusters within a linear response approach, taking into account the in-medium Mott effects on cluster appearance, through a density-dependent momentum cut-off. We find that spinodal instabilities and associated growth rates are severely affected by the presence of light clusters and, in particular, by the treatment of in-medium effects, foreshadowing intriguing consequences for fragment formation in heavy-ion collisions and in the broader astrophysical context.

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arXiv2022

Finite-temperature infinite matter with effective-field-theory-inspired energy-density functionals

Finite-temperature infinite matter is analyzed with the recently introduced effective-fieldtheory(EFT)-inspired YGLO (Yang-Grasso-Lacroix-Orsay) and ELYO (extended Lee-Yang, Orsay) functionals, which are designed to describe very low-density regimes in symmetric (YGLO) and in pure neutron (YGLO and ELYO) matter. The article deals with neutron matter and aims to verify whether the use of these functionals allows us to correctly incorporate finite-temperature effects. We compare our results for some relevant thermodynamical quantities with the corresponding ones computed with a chosen reference ab-initio model, namely the many-body-perturbation-theory scheme. We validate the reliability of both EFT-inspired functionals at least at rather low densities and not too high temperatures and we discuss the effects related to the effective mass. We conclude that, at the present stage, the ELYO functional, having a higher neutron effective mass around saturation (closer to ab-initio values), allows us to describe finite-temperature properties more satisfactorily, in better agreement with ab-initio predictions up to higher densities and temperatures, compared to YGLO.

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arXiv2021

Application of an ab-initio-inspired energy density functional to nuclei: impact of the effective mass and the slope of the symmetry energy on bulk and surface properties

The YGLO (Yang-Grasso-Lacroix-Orsay) functional is applied for the first time to investigate ground-state properties of different isotopic chains, from Oxygen to Lead. Mean-field Hartree-Fock calculations are carried out to analyze global trends for separation energies, binding energies, radii, neutron skins, and density profiles. We have three objectives: i) we study whether this functional leads to a reasonable description of ground-state properties (despite the fact that it was not adjusted on nuclei) and we discuss the associated limitations; ii) we investigate whether the correct description of the low-density nuclear gas, which is the peculiarity of this functional, has any relevant impact on predictions for nuclei; iii) we connect nuclear energies, radii and density profiles with properties of the corresponding equations of state of infinite matter. In particular, we identify a link existing between the isoscalar effective mass and spatial properties in neutron-deficient nuclei, namely proton radii and tails of proton densities. On the other side, we show that the slope of the symmetry energy is connected with spatial properties in neutron-rich nuclei: the slope computed at saturation density is related to neutron skin thicknesses, as already well known, whereas the slope calculated at lower densities is linked to the tails of neutron densities. The YGLO effective mass turns out to be quite low. Directions to improve this aspect are explored and suggested at the end of the manuscript.

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arXiv2020

Towards a power counting in nuclear energy-density-functional theories through a perturbative analysis

We illustrate a step towards the construction of a power counting in energy-density-functional (EDF) theories, by analyzing the equations of state (EOSs) of both symmetric and neutron matter. Within the adopted strategy, next-to-leading order (NLO) EOSs are introduced which contain renormalized first-order-type terms and an explicit second-order finite part. Employing as a guide the asymptotic behavior of the introduced renormalized parameters, we focus our analysis on two aspects: (i) With a minimum number of counterterms introduced at NLO, we show that each energy contribution entering in the EOS has a regular evolution with respect to the momentum cutoff (introduced in the adopted regularization procedure) and is found to converge to a cutoff-independent curve. The convergence features of each term are related to its Fermi-momentum dependence. (ii) We find that the asymptotic evolution of the second-order finite-part coefficients is a strong indication of a perturbative behavior, which in turns confirms that the adopted strategy is coherent with a possible underlying power counting in the chosen Skyrme-inspired EDF framework.

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arXiv2019

Sequential Heavy Ion Double Charge Exchange Reactions and the Link to Double $β$-decay

Heavy ion double charge exchange reactions are described by sequential meson-exchange, corresponding to a double single charge exchange (DSCE) reaction mechanism. The theoretical formulation is discussed. The fully quantum mechanical distorted wave 2-step calculations are shown to be reproduced very well by approximating the intermediate propagator by its pole part. The role of ion-ion elastic interactions is discussed. As a first application, calculations are performed for the reaction $^{40}$Ca $(^{18}$O $,^{18}$Ne $)^{40}$Ar at 15 AMeV. Results are compared to the data measured at LNS by the NUMEN Collaboration. The common aspects of DSCE reactions and double $β$- decay are discussed by a detailed comparison of the respective nuclear matrix elements (NME).

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arXiv2019

The symmetry energy of the nuclear EoS: a study of collective motion and low-energy reaction dynamics in semiclassical approaches

In the framework of mean-field based transport approaches, we discuss recent results concerning collective motion and low-energy heavy ion reactions involving neutron-rich systems. We focus on aspects which are particularly sensitive to the isovector terms of the nuclear effective interaction and the corresponding symmetry energy. As far as collective excitations are concerned, we discuss the mixed nature of dipole oscillations in neutron-rich systems. On the other hand, for reactions close to the Coulomb barrier, we investigate the structure of pre-equilibrium collective dipole oscillations, focusing on their sensitivity to the symmetry energy behavior below normal density. Nucleon emission is also considered within the same context. The possible impact of other relevant terms of the nuclear effective interaction on these mechanisms is also examined. From this analysis we expect to put further constraints on the nuclear Equation of State, of crucial importance also in the astrophysical context.

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arXiv2013

Pairing effects on spinodal decomposition of asymmetric nuclear matter

We investigate the impact of pairing correlations on the behavior of unstable asymmetric nuclear matter at low temperature. We focus on the relative role of the pairing interaction, coupling nucleons of the same type (neutrons or protons), with respect to the symmetry potential, which enhances the neutron-proton attraction, along the clusterization process driven by spinodal instabilities. It is found that, especially at the transition temperature from the normal to the superfluid phase, pairing effects may induce significant variations in the isotopic content of the clusterized matter. This analysis is potentially useful to gather information on the temperature dependence of nuclear pairing and, in general, on the properties of clusterized low-density matter, of interest also in the astrophysical context.

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