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Gianluca Colò

Publications and source records attributed to Gianluca Colò.

At least 19 recordsLinked to original sources
arXiv2026

Emulator-Assisted Nuclear DFT Inference and Its Consequences for the Structure of Neutron Stars

Nuclear density functional theory provides a unified description of finite nuclei and bulk nuclear matter, and is widely used to model the neutron star equation of state. However, extrapolations to supra-saturation densities require a quantified treatment of uncertainties arising from parameter estimation and functional choices. We present an updated Bayesian inference of a Skyrme energy density functional augmented by a flexible meta-model density dependence at high density. Nuclear observables are computed using a Gaussian emulator of the publicly available Milano HFBCS-QRPA code, enabling efficient exploration of a high-dimensional parameter space. Relative to previous analyses, we extend the calibration set with isospin-sensitive data, including masses and charge radii along selected Ca and Sn isotopic chains, and updated constraints from giant monopole resonances. The resulting posteriors are further constrained by \emph{ab initio} neutron-matter calculations and astrophysical observations, including recent NICER measurements, yielding consistent crust and core properties of catalyzed NS compatible with current constraints. Bulk nuclear-matter parameters are well approximated by a multivariate Gaussian with covariance matrix provided for direct reuse, while several finite-nucleus parameters exhibit pronounced non-Gaussianity.

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arXiv2026

Electron-capture rates in the medium-mass nuclei $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge within deformed quasiparticle random-phase approximation

Electron-capture (EC) rates in medium-mass nuclei are governed by Gamow--Teller (GT) strength distributions and provide important input for stellar weak-interaction processes. In this work, we investigate the deformation dependence of the GT strengths and stellar EC rates in selected medium-mass nuclei in and near the $pf$ shell, namely $^{48}$Ti, $^{56}$Ni, $^{60}$Zn, and $^{64}$Ge. The GT$^{(+/-)}$ strength distributions are calculated in the deformed quasiparticle random-phase approximation (DQRPA) on a single-particle basis obtained by the Skyrme SGII interaction, while the stellar EC rates are evaluated from the resulting $B(\mathrm{GT}^+)$ strengths using the standard phase-space formalism. The potential-energy curves are used to identify shape softness and possible shape coexistence in the nuclei under consideration. We find that deformation strongly modifies the GT strength distributions by changing the centroid energies, resonance splitting, and fragmentation patterns. In particular, a pronounced shape dependence of the GT$^{(+/-)}$ strengths is found for $^{56}$Ni and $^{64}$Ge, whereas $^{60}$Zn is characterized by a favoured prolate minimum and $^{48}$Ti exhibits a soft near-spherical/prolate landscape. By contrast, the corresponding EC rates are generally much less sensitive to deformation than the differential GT response itself, except at low temperatures and low densities where the low-lying GT$^+$ strength becomes decisive because of the negative EC $Q$-value in the electron phase space. Available charge-exchange data for $^{48}$Ti and $^{56}$Ni are used as benchmarks of the model predictions. The present results provide microscopic constraints on the role of deformation and shape coexistence in stellar weak rates for selected medium-mass nuclei, including proton-rich isotopes near the $N = Z$ line.

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arXiv2026

Microscopic mechanism of the Fayans pairing for the enhancement of charge radii

The Fayans energy density functional (EDF), and in particular its pairing sector, have been claimed to be able to reproduce the experimental data of charge radii in many instances. A particularly intriguing case is that of the $ \mathrm{Ca} $ isotopes between $ A = 40 $ and $ 48 $, where charge radii exhibit a "bell shape". In our work, we examine the microscopic origin of this behaviour. We prepare in total $ 25 $ paramerizations of the Fayans-like pairing interaction, that are equivalent in fulfilling the same criteria for the reproduction of empirical pairing gaps. We find that both the density and the density-gradient dependence of the pairing interaction are important to reproduce the well-known enhancement of charge radii in the open-shell nuclei, leading to the "bell shape" behaviour of $ \mathrm{Ca} $ isotopes. In particular, this originates from the repulsive nature of the rearrangement potential, and cannot simply be mocked up by a refit of the pairing strength. At the same time, we notice some drawbacks of the Fayans standard EDFs, that may call for investigating a more general form of it.

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arXiv2026

Improving the efficiency of Hartree--Fock--Bogoliubov solvers in 3D space

The solution of the three-dimensional Schrödinger-like single-particle equations that appear in Kohn Sham density functional theory, as well as in other contexts, for large systems and without any symmetry, requires efficient and robust numerical algorithms. Conventional methods suffer from slow convergence and require careful tuning, depending on the spatial discretization. Conjugate gradient methods combined with preconditioning have been proposed to accelerate the convergence of symmetry-unrestricted Skyrme energy density functionals; however, their effectiveness may depend on the design of a preconditioner. In this work, we introduce the generalized conjugate gradient method for the self-consistent solution of the Hartree--Fock--Bogoliubov equations, which eliminates the need for problem-dependent preconditioning and improves the convergence speed of currently available methods. The performance of the proposed algorithm is demonstrated on representative nuclear systems, showing improved convergence behavior compared to standard approaches. The proposed method ultimately provides a promising tool for systematic studies of superheavy, strongly deformed, and drip-line nuclei.

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arXiv2026

Bayesian Inference of the Landau Parameter $G'_0$ from Joint Gamow-Teller Measurements

The Landau-Migdal parameter $G'_0$ characterizes the main part of the spin-isospin dependent nucleon-nucleon interaction. Consequently, the $G'_0$ is closely related to the Gamow-Teller resonance (GTR), the beta and double-beta decay rates of finite nuclei, the response of hot and dense nucleonic matter that modifies the neutrino-nucleon absorption rates in core-collapse supernovae (CCSNe) and binary neutron star (BNS) mergers, and finally the critical density for pion condensation in neutron stars. In this letter, for the first time, we report the $G'_0$ with quantified uncertainty in the framework of Bayesian inference, using a self-consistent standard Skyrme Random Phase Approximation (RPA) model and joint constraints from experimental GTR measurements on $^{208}\mathrm{Pb}$, $^{132}\mathrm{Sn}$, $^{90}\mathrm{Zr}$. Our extracted $G_0'$ is $0.48\pm0.034$, which is close to the prediction of a few existing Skyrme models that consider spin-isospin observables but smaller than the traditional ones extracted from pion-exchange models. We hint to possible reasons for this deviation, like the value of the nucleon effective mass $\frac{m^*}{m}$. The $G_0'$ values extracted in this work may guide the construction of new energy density functionals that aims to self-consistently describe the dense matter properties in the spin-isospin channel.

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arXiv2026

Gorkov algebraic diagrammatic construction for infinite nuclear matter

We propose a novel many-body truncation for Gorkov self-consistent Green's function (SCGF) theory where pairing correlations are handled at first order, while dynamical correlations are described using the particle-number-conserving Dyson-SCGF scheme up to third order in the algebraic diagrammatic construction. The new method is enabled by the introduction of a scheme that allows to approximate the Gorkov propagator in terms of a particle-number-conserving optimized reference state. The approach provides state-of-the-art predictions of the equation of state and spectral properties of infinite nuclear matter at zero temperature and in the presence of pairing. We find satisfactory results using modern saturating Hamiltonians at next-to-next-to-leading order in chiral effective field theory.

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arXiv2026

Gamow-Teller strength of $^{12,14,16}$C within deformed quasiparticle random-phase approximation

We investigate the Gamow-Teller (GT) transition strength distributions in the light carbon isotopes $^{12,14,16}$C within the framework of the deformed quasiparticle random-phase approximation (DQRPA). Nuclear deformation is explicitly incorporated through Skyrme Hartree-Fock mean-field calculations combined with the QRPA formalism. The residual particle-hole $(p-h)$ and particle-particle $(p-p)$ interactions are derived from Brückner $G$-matrix calculations based on the CD-Bonn potential, and their impact on the low-lying GT strengths is systematically examined by varying the corresponding interaction strengths. We find that nuclear deformation, associated with a reduced spin-orbit strength, plays a significant role in interpreting the GT strength distribution of $^{12}$C. In contrast, the calculated GT$^{(-)}$ strength distribution of $^{14}$C in the spherical limit reproduces the essential features of the experimental $(p,n)$ charge-exchange data. The case of $^{16}$C reveals additional high-lying GT strength associated with deformation-induced configuration mixing.

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arXiv2026

Basis Representation for Nuclear Densities from Principal Component Analysis

We develop an efficient method to represent nuclear densities using basis functions extracted via Principal Component Analysis (PCA). Applying PCA to densities of 75 nuclei calculated with the relativistic continuum Hartree-Bogoliubov (RCHB) theory yields an orthogonal set of components that efficiently capture the dominant features of nuclear density distributions, which can be used as basis functions for nuclear density representation. The first five basis functions account for more than 99.999\% of the total variance, demonstrating the efficiency of these PCA basis functions. The PCA basis achieves significantly higher accuracy and faster convergence than the Fourier-Bessel and Sum-of-Gaussians methods for reconstructing both theoretical and experimental densities. This approach provides an efficient and robust representation of nuclear densities, offering a practical tool for experimental density representation and for theories where densities play a central role, such as the orbital-free density functional theory, or the double folding model for nuclear reactions.

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arXiv2026

Non-local orbital-free density functional theory incorporating nuclear shell effects

Incorporating nuclear shell effects within the framework of orbital-free density functional theory (DFT) has remained a longstanding challenge in nuclear physics. While the Hohenberg-Kohn theorem formally guarantees the existence of an orbital-free density functional that is capable of describing all many-body effects, including shell effects, practical attempts since the 1970s have consistently failed to capture such effects. This persistent difficulty has even led to the misconception that the orbital-free DFT is inherently unable to describe nuclear shell effects. Here we develop a {\it non-local} orbital-free DFT approach for atomic nuclei and demonstrate that nuclear shell effects can be successfully incorporated into the orbital-free DFT through the construction of a non-local kinetic energy density functional. In particular, we show that the non-local orbital-free functional yields a nucleon localization function that, as an established indicator of shell effects, exhibits consistent behavior with the exact Kohn-Sham solution.

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arXiv2025

Impact of ground-state properties and collective excitations on the Skyrme ansatz: a Bayesian study

State-of-the-art models based on nuclear Density Functional Theory are successful in the description of nuclei throughout the whole nuclear chart. Among them, some differences arise regarding their accuracy. For a given nuclear model, this depends on the procedure adopted to determine the parameters, and, at the same time, new experimental findings constantly challenge theory. In the present work, we present a Bayesian inference study aimed at assessing the performance of the Skyrme Energy Density Functional. For the sake of simplicity and clarity, we restrict to spherical, double-magic nuclei, giving equal emphasis to ground-state and dynamical properties. Our basic constraints are: i) masses and charge radii, which are known to be very sensitive to the saturation energy and density; ii) spin-orbit splittings, which are associated with the spin-orbit parameter(s); iii) the electric dipole polarizability and parity-violating asymmetry, which are associated with the density dependence of the symmetry energy; iv) the excitation energy of the Isoscalar Giant Monopole Resonance, to constrain the nuclear matter incompressibility; v) the energy-weighted sum rule of the Isovector Giant Dipole Resonance, to account for the isovector effective mass; and vi) the excitation energy of the Isoscalar Quadrupole Resonance, that is related to the isoscalar effective mass. In this way, we test the Skyrme ansatz in a statistically meaningful way, by determining the posterior distributions of the parameters as well as their correlation, and discussing a possible strategy for future developments.

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arXiv2025

Mirror-skin thickness: a possible observable sensitive to the charge symmetry breaking energy density functional

We propose a new observable, named the mirror-skin thickness, in order to extract the strength of the charge symmetry breaking (CSB) term in an energy density functional (EDF). The mirror-skin thickness of $ N = 20 $ isotones and $ Z = 20 $ isotopes is studied by using Hartree-Fock-Bogoliubov (HFB) calculations with various Skyrme EDFs and adding CSB and charge independence breaking (CIB) terms. It is shown that the mirror-skin thickness is sensitive only to the CSB EDF, but hardly depends on either the isospin symmetric part of the nuclear EDF or the CIB term. Therefore, this observable can be used to extract the magnitude of the CSB term in the EDF quantitatively, either from experimental data or ab initio calculations. We have studied the accuracy in the mirror-skin thickness that is needed to extract sensible information. Our study may also help to understand the inconsistency between the strength of the phenomenological CSB and that extracted from ab initio calculations [Naito et al. Nuovo. Cim. C 47, 52 (2024)]. Among possible mirror pairs for experimental study, we propose the mirror-skin thickness between $ {}^{42} \mathrm{Ca} $ and $ {}^{42} \mathrm{Ti} $, which could be accessed in future experiments in RIBF and/or FRIB.

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arXiv2025

Direct proton transfer on $^{46}$Ar supports the presence of a charge density bubble linked to a novel nuclear structure below $^{48}$Ca

The $^{46}$Ar($^3$He,d)$^{47}$K reaction was performed in inverse kinematics using a radioactive $^{46}$Ar beam produced by the SPIRAL1 facility at GANIL and a cryogenic $^{3}$He target. The AGATA-MUGAST-VAMOS setup allowed the coincident measurement of the $γ$ rays, deuterons and recoiling $^{47}$K isotopes produced by the reaction. The relative cross sections towards the proton-addition states in $^{47}$K point towards a depletion of the $πs_{1/2}$ shell. The experimental findings are in good agreement with ab initio calculations, which predict that $^{46}$Ar exhibits a charge density bubble associated with a pronounced proton closed-shell character.

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arXiv2025

Synthesis of superheavy elements in the outer crust of a magnetar

A theoretical understanding of a possible mechanism for synthesizing superheavy elements in the outer crust of magnetars is presented. We demonstrate that such a mechanism can be present whenever the baryon density in the outer crust of a neutron star reaches values around $10^{-2}$ fm$^{-3}$. This scenario could be realized in magnetars with hypothetical large magnetic fields, $B \geq 10^{18}$ G. Under such conditions, the Coulomb lattice, formed by ionized nuclei, enables a mechanism that synthesizes superheavy elements.

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arXiv2024

Nuclear Pairing Energy vs Mean Field Energy: Do They Talk To Each Other For Searching The Energy Minimum?

We study the evolution of the total binding energy (TBE) and pairing energy of Pb, Hg and Ar isotopes, as a function of the nuclear deformation. As for the nuclear model, we exploit a deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc), and a deformed Skyrme Hartree-Fock plus BCS model. It is found that the dependence of pairing energy on the deformation is strongly correlated to that of the mean field energy, which is obtained by subtracting the pairing energy from the TBE; in other words, the energy minimum characterized by a large negative mean field energy has a smaller negative pairing energy or, equivalently, a smaller positive pairing gap, while a stronger pairing energy is found in the region away from the minimum of the total energy. Consequently, the two energies show an anti-symmetric feature in their deformation dependence, although the energy scales are very different. Moreover, since the pairing energy has a negative sign with respect to to the pairing gap, the evolution of mean field energy follows closely that of the pairing gap. This implies that the pairing energy (or pairing gap) and the mean field energy talk to each other and work together along the potential energy curve to determine the energy minimum and/or the local minimum.

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arXiv2024

Ab initio Green's functions approach for homogeneous nuclear matter

Homogeneous nuclear matter is investigated using the \textit{ab initio} Self-consistent Green's function (SCGF) approach with nuclear interactions based on chiral effective field theory. The employed method, which combines the state-of-the-art algebraic diagrammatic construction approximation at third order with Gorkov correlations, is capable of computing both the equation of state (EOS) and single-particle properties of nuclear matter. The EOS calculated with our approach and coupled-cluster theory are shown to agree very well. The one-nucleon spectral functions and the momentum distributions are discussed to gain insights into the dynamics of the interacting nuclear matter.

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arXiv2024

Symmetry Energy from Two-Nucleon Separation Energies of Pb and Ca Isotopes

We investigate the symmetry energy in relation with the two-proton and two-neutron separation energies using different nuclear mass data. For this aim, we exploit the deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc), FRDM2012 and AME2020 data. First, we study the two-proton and two-neutron separation energies in Pb and Ca isotopes by subtracting the contribution of Coulomb energy. They show a strong correlation with neutron number as well as with the neutron skin thickness. By taking the relative difference of both separation energies, we derive the symmetry energy from Ca and Pb isotopes. Since the nuclear surface contributes to the symmetry energy, we deduce the volume symmetry energy by subtracting the surface contribution using several mass models. The obtained symmetry energy coefficient, $a_{sym}$, is 20.0 $\sim $ 22.7 MeV for Pb isotopes and 18.7 $\sim$ 19.3 MeV for Ca isotopes from the DRHBc mass table data, while the results from other mass tables are 19.6 $\sim$ 22.1 (20.7 $\sim$ 22.3) MeV for Pb isotopes and 18.9 $\sim$ 19.0 (19.6 $\sim$ 19.7) MeV for Ca isotopes from AME2020 (FRDM2012) data. The volume contribution to the asymmetry coefficient, $a_{sym}^v$, which depends on the ratio of the surface to the volume energy coefficients, $a_s / a_v$, is also provided for each mass model. Since the ratio $a_s / a_v$ is neither determined by nuclear theory, nor by experimental data, we have investigated $a_{sym}^v$ by using the ratio $a_s / a_v$ as a free parameter, and have obtained $a_{sym}^v = $ 27.0 MeV, almost irrespective of nuclear model and isotopic chain, with the ratio $a_s / a_v$ constrained as $a_s / a_v = 1.10 \sim 1.13$.

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arXiv2023

Microscopic study of $M$1 resonances in Sn isotopes

The magnetic dipole ($M$1) resonances of even-even $^{112-120, 124}$Sn isotopes are investigated in the framework of the self-consistent Skyrme Hartree-Fock (HF) + BCS and Quasiparticle Random Phase Approximation (QRPA). The Skyrme energy density functionals SLy5 and T11 with and without tensor terms are adopted in our calculations. The mixed type pairing interaction is used to take care of the pairing effect for open-shell nuclei both in the ground and excited states calculations. The calculated magnetic dipole strengths are compared with available experimental data. The QRPA results calculated by SLy5 and T11 with tensor force show a better agreement with the experimental data than those without the tensor force. By analyzing the HF and QRPA strength distributions of $^{112}$Sn and $^{124}$Sn, we discuss the effect of tensor force on the $M$1 resonances in detail. It is found that the $M$1 resonance is sensitive to the tensor interaction, and favors especially a negative triplet-odd tensor one. Depending on the nucleus, a quenching factor of the $M$1 operator of about 0.71-0.95 is needed to reproduce the total observed transition strength. In our calculations, we also find some low-lying, pygmy-type magnetic dipole states distributed below 6.0 MeV, and they are formed mainly from the neutron configuration $ν$2$d_{5/2}$$\rightarrow$$ν$2$d_{3/2}$.

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