Searcharxiv⌕ Search

arXiv subjects

M. Centelles

Publications and source records attributed to M. Centelles.

At least 19 recordsLinked to original sources
arXiv2024

Equation of State of Hot Neutron Star Matter using Finite Range Simple Effective Interaction

The equation of state of hot neutron star matter of n+p+e+$\mu$ composition in $\beta$-equilibrium is studied for both neutrino-free isothermal and neutrino-trapped isentropic conditions, using the formalism where the thermal evolution is built upon its zero-temperature predictions in a self-consistent manner. The accuracy of the parabolic approximation, often used in the finite temperature calculation of hot neutron star matter, is verified by comparing with the results obtained from the exact evaluation in the neutrino-free neutron star matter. The equation of state of neutrino-trapped isentropic matter at low entropic condition, relevant to the core-collapsing supernovae, is formulated. In the isentropic matter, the particle fractions and equation of state have marginal variance as entropy per particle varies between 1 to 3 (in the unit of k$_B$), but the temperature profile shows marked variation. The isentropes are found to be much less sensitive to the nuclear matter incompressibility, but have a large dependence on the slope parameter L. The bulk properties of the neutron stars predicted by the isentropic equation of state for different entropy are calculated. A model calculation for the early stage evolution of the protoneutron star to neutron star configuration is also given.

nucl-th↗
arXiv2023

Correlations between charge radii differences of mirror nuclei and stellar observables

The correlation between the charge radii differences in mirror nuclei pairs and the neutron skin thickness has been studied with the so-called finite range simple effective interaction over a wide mass region. The so far precisely measured charge radii difference data within their experimental uncertainty ranges in the 34Ar-34S, 36Ca-36S, 38Ca-38Ar, and 54Ni-54Fe mirror pairs are used to ascertain an upper limit for the slope parameter of the nuclear symmetry energy L $\approx$ 100 MeV. This limiting value of L is found to be consistent with the upper bound of the NICER PSR J0740+6620 constraint at 1$σ$ level for the radius R$_{1.4}$ of 1.4 M$_\odot$ neutron stars. The lower bound of the NICER R$_{1.4}$ data constrains the lower limit of L to $\approx$ 70 MeV. Within the range for L = 70-100 MeV the tidal deformability $Λ^{1.4}$ constraint, which is extracted from the GW170817 event at 2$σ$ level, and the recent PREX-2 and CREX data on the neutron skin thickness are discussed.

nucl-th↗
arXiv2022

The finite range simple effective interaction including tensor terms

The prediction of single particle level crossing phenomenon between $2p_{3/2}$ and $1f_{5/2}$ orbitals in $Ni$- and $Cu$-isotopic chains by the finite range simple effective interaction without requiring the tensor part is discussed. In this case the experimentally observed crossing could be studied as a function of nuclear matter incompressibility, $K(ρ_0)$. The estimated crossing for the neutron number $N$=46 could be reproduced by the equation of state corresponding to $K(ρ_0)$=240 MeV. However, the observed proton gaps between the $1h_{11/2}$ and $1g_{7/2}$ shells in $Sn$ and $Sb$ isotopic chain, and the neutron gaps between the $1i_{13/2}$ and $1h_{9/2}$ shells in $N$=82 isotones, as well as the shell closure properties at $N$=28 require explicit consideration of a tensor part as the central contribution is not enough to initiate the required level splittings.

nucl-th↗
arXiv2021

The N=50 and Z=28 shell closure revisited

Recent experiments performed in neutron-rich copper isotopes have revealed a crossing in the nucleus $^{75}$Cu between the $3/2^-$ and $5/2^-$ levels, which correspond to the ground-state and the first excited state in isotopes with mass number below $A =75$. Due to the strong single-particle character of these states, this scenario can be investigated through the analysis of the proton spectrum provided by mean-field models in nickel isotopes with neutron numbers between $N$=40 and $N$=50. In this work we show that the aforementioned crossing is mainly driven by the mean-field provided by the effective nucleon-nucleon and spin-orbit interactions. We also analyze the impact of the tensor interaction, and find that in some mean-field models it is essential to reproduce the crossing of the 2$p_{3/2}$ and 1$f_{5/2}$ proton single-particle levels, as in the case of the SAMi-T Skyrme force and the D1M Gogny interaction, whereas in other cases, as for example the SLy5 Skyrme force, a reasonable tensor force appears to be unable to modify the mean-field enough to reproduce this level crossing. Finally, in the calculations performed with the so-called simple effective interaction (SEI), it is shown that the experimental data in nickel and copper isotopes considered in this work can be explained satisfactorily without any explicit consideration of the tensor interaction.

nucl-th↗
arXiv2020

Microscopic-Macroscopic Approach for Ground-State Energies Based on the Gogny Force with the Wigner-Kirkwood Averaging Scheme

In the previous paper I \cite{bhagwat20} we have shown that self-consistent Extended Thomas-Fermi (ETF) potentials and densities associated with a given finite-range interaction can be parametrized by generalized Fermi distributions. As a next step, a comprehensive calculation of ground-state properties of a large number of spherical and deformed even-even nuclei is carried out in the present work using the Gogny D1S force within the ETF scheme. The parametrized ETF potentials and densities of paper I are used to calculate the smooth part of the energy and the shell corrections within the Wigner-Kirkwood semiclassical averaging scheme. It is shown that the shell corrections thus obtained, along with a simple liquid drop prescription, yield a good description of ground-state masses and potential energy surfaces for nuclei spanning the entire periodic table.

nucl-th↗
arXiv2020

Structure and composition of inner crust of neutron stars from Gogny interactions

The detailed knowledge of the inner crust properties of neutron stars might be important to explain different phenomena such as pulsar glitches or the possibility of an {\it r-process} site in neutron star mergers. It has been shown in the literature that quantal effects like shell correction or pairing may play a relevant role to determine the composition of the inner crust of the neutron star. In this paper we construct the equation of state of the inner crust using the finite-range Gogny interactions, where the mean field and the pairing field are calculated with same interaction. We have used the semiclassical Variational Wigner-Kirkwood method along with shell and pairing corrections calculated with the Strutinsky integral method and the BCS approximation, respectively. Our results are compared with those of some popular models from the literature. We report a unified equation of state of the inner crust and core computed with the D1M* Gogny force, which was specifically fabricated for astrophysical calculations.

nucl-th↗
arXiv2020

Comment on the paper Eur. Phys. J. A (2019) 55:150

The conclusions of the study published as Eur. Phys. J. A (2019) 55:150 questioning the adequacy of the recently proposed Gogny D1M* interaction for finite-nuclei calculations using harmonic oscillator (HO) basis are revised. The existence of an instability in finite nuclei for D1M* when coordinate-space methods are used to solve the HF equations (as shown in Eur. Phys. J. A(2019) 55:150) is independently confirmed using a computer code based on a quasi-local approximation (QLA) to the HF energy density with finite-range forces. We confirm that the most affected quantity in the coordinate-space calculation is the spatial density at the origin. Our study reveals that some findings concerning these instabilities are not easy to reconcile with the arguments used in Eur. Phys. J. A (2019) 55:150. For instance, some nuclei such as $^4$He and $^{40}$Ca, which diverge in HF mesh-point calculations performed with D1M*, become perfectly stable when Coulomb force is switched off. We have also found instabilities in some nuclei when the D1M interaction is used. Finally, a connection between the occupancy of $s$-orbitals near the Fermi level and the appearance of instabilities is observed. Several convergence and stability studies are performed with HO basis of different sizes and oscillator parameters to demonstrate the robustness of the D1M* results for finite nuclei when the HO basis is used.

nucl-th↗
arXiv2020

Constraints from GW170817 on the bulk viscosity of neutron star matter and the r-mode instability

We perform a systematic study of the dependence of the r-mode phenomenology in normal fluid pulsar neutron stars on the symmetry energy slope parameter $L$. An essential ingredient in this study is the bulk viscosity, which is evaluated consistently for several equations of state corresponding to different values of the slope parameter $L$. Direct Urca processes, which are allowed from a critical $L$-value onwards, enhance the bulk viscosity and have large influence on the $r$-mode features, such as the instability boundary and spin-down properties of newborn neutron stars. The magnitude of the changes in the $r$-mode properties induced by the direct Urca processes are driven by the $L$-value of the equation of state and the mass of the pulsar. The study has been done by using a family of equations of state of $β$-equilibrated neutron star matter obtained with the finite range simple effective interaction, which provides realistic results for nuclear matter and finite nuclei properties. These equations of state predict the same properties in symmetric nuclear matter and have the same value of the symmetry energy parameter, $E_s(ρ_0)$, but differ in the slope parameter $L$. The range chosen for the variation of $L$ is decided from the tidal deformability data extracted from the GW170817 event and the maximum mass constraint.

nucl-th↗
arXiv2020

GW170817 constraints analyzed with Gogny forces and momentum-dependent interactions

A set of equations of state obtained from finite-range Gogny forces and momentum-dependent interactions is used to investigate the recent observation of gravitational waves from the binary neutron star merger GW170817 event. For this set of interactions, we have calculated the neutron star tidal deformabilities (related to the second Love number), the mass-radius diagram, and the moment of inertia~($I$). The $I$-Love relation has been verified. We also have found strong correlations among the tidal deformability of the canonical neutron star, its radius, and the derivatives of the nuclear symmetry energy at the saturation density. Most of the obtained results are located within the constraints of the tidal deformabilities extracted from the GW170817 detection.

nucl-th↗
arXiv2019

Study of the core-crust transition in neutron stars with finite-range interactions: the dynamical method

The properties of the core-crust transition in neutron stars are investigated using effective nuclear forces of finite-range. Special attention is paid to the so-called dynamical method for locating the transition point, which, apart from the stability of the uniform nuclear matter against clusterization, also considers contributions due to finite-size effects. In particular, contributions to the transition density and pressure from the direct and exchange energies are carefully analyzed. To this end, finite-range forces of Gogny, Modified Gogny Interaction (MDI) and Simple Effective Interaction (SEI) types are used in the numerical applications. The results from the dynamical approach are compared with those from the popular thermodynamical method that neglects the surface and Coulomb effects in the stability condition. The dependence of the core-crust transition on the stiffness of the symmetry energy of the finite-range models is also addressed. Finally, we analyze the impact of the transition point on the mass, thickness and fraction of the moment of inertia of the neutron star crust. Prominent differences in these crustal properties of the star are found between using the transition point obtained with the dynamical method or the thermodynamical method. It is concluded that the core-crust transition needs to be ascertained as precisely as possible in order to have realistic estimates of the observed phenomena where the crust plays a significant role.

nucl-th↗
arXiv2018

Gogny forces in the astrophysical context

The most successful Gogny interactions of the D1 family, namely D1S, D1N and D1M, suffer the common problem of a too soft neutron matter equation of state at high density, which prevents them from predicting a maximal mass of neutron stars of two solar masses, as required by recent astronomical observations. To cure this deficiency, we have proposed recently a reparametrization of the D1M force by fine tuning the slope of the symmetry energy in such a way that it preserves the ground-state properties of D1M in finite nuclei and also describes successfully the global properties of neutron stars, in particular its maximal mass, in consonance with the observational data. In this contribution we revisit this reparametrization by discussing two modified Gogny forces, dubbed D1M$^*$ and D1M$^{**}$.

nucl-th↗
arXiv2018

Comment on the manuscript 1806.02080v1 entitled "Spurious finite-size instabilities of a new Gogny interaction suitable for astrophysical applications"

The conclusions of the manuscript 1806.02080v1 questioning the adequacy of the recently proposed Gogny D1M* interaction for finite nuclei calculations using harmonic oscillator (HO) basis are revised. Several convergence and stability studies are performed with HO basis of different sizes and oscillator parameters and the results show the robustness of the D1M* results for finite nuclei. This analysis is also extended to beyond mean-field calculations of generator-coordinate-method type with D1M*. On the other hand, the existence of a finite-size instability in finite nuclei when coordinate space methods are used to solve the HF equations (as shown in 1806.02080v1) is independently confirmed for D1M* using an in-house computer code based on a quasilocal approximation to the HF exchange potential. We confirm that the most affected quantity in the coordinate space calculation is the spatial density at the origin, but integrated quantities like binding energies or radii show a plateau against the number of iterations, where they are consistent with the values from the HO basis calculation, before diverging for a larger number of iterations. A connection between the last occupied s-orbital in the nucleus and the appearance of instabilities in coordinate space is observed.

nucl-th↗
arXiv2017

Influence of the nuclear matter equation of state on the r-mode instability using the finite-range simple effective interaction

The characteristic physical properties of rotating neutron stars under the r-mode oscillation are evaluated using the finite-range simple effective interaction. Emphasis is given on examining the influence of the stiffness of both the symmetric and asymmetric parts of the nuclear equation of state on these properties. The amplitude of the r-mode at saturation is calculated using the data of particular neutron stars from the considerations of "spin equilibrium" and "thermal equilibrium". The upper limit of the r-mode saturation amplitude is found to lie in the range 10^{-8}-10^{-6}, in agreement with the predictions of earlier work.

nucl-th↗
arXiv2017

New Gogny interaction suitable for astrophysical applications

The D1 family of parametrizations of the Gogny interaction commonly suffers from a rather soft neutron matter equation of state that leads to maximal masses of neutron stars well below the observational value of two solar masses. We propose a reparametrization scheme that preserves the good properties of the Gogny force but allows one to tune the density dependence of the symmetry energy, which, in turn, modifies the predictions for the maximum stellar mass. The scheme works well for D1M, and leads to a new parameter set, dubbed D1M*. In the neutron-star domain, D1M* predicts a maximal mass of two solar masses and global properties of the star in harmony with those obtained with the SLy4 Skyrme interaction. By means of a set of selected calculations in finite nuclei, we check that D1M* performs comparably well to D1M in several aspects of nuclear structure in nuclei.

nucl-th↗
arXiv2017

Higher-order symmetry energy and neutron star core-crust transition with Gogny forces

We study the symmetry energy and the core-crust transition in neutron stars using the finite-range Gogny nuclear interaction and examine the deduced crustal thickness and crustal moment of inertia. We start by analyzing the second-, fourth- and sixth-order coefficients of the Taylor expansion of the energy per particle in powers of the isospin asymmetry for Gogny forces. These coefficients provide information about the departure of the symmetry energy from the widely used parabolic law. The neutron star core-crust transition is evaluated by looking at the onset of thermodynamical instability of the liquid core. The calculation is performed with the exact (i.e., without Taylor expansion) Gogny EoS for the core, and also with its Taylor expansion in order to assess the influence of isospin expansions on locating the inner edge of neutron star crusts. It is found that the properties of the core-crust transition derived from the exact EoS differ from the predictions of the Taylor expansion even when the expansion is carried through sixth order in the isospin asymmetry. Gogny forces, using the exact EoS, predict the ranges $0.094 \text{ fm}^{-3} \lesssim ρ_t \lesssim 0.118\text{ fm}^{-3}$ for the transition density and $0.339 \text{ MeV fm}^{-3} \lesssim P_t \lesssim 0.665 \text{ MeV fm}^{-3}$ for the transition pressure. The transition densities show an anticorrelation with the slope parameter $L$ of the symmetry energy. The transition pressures are not found to correlate with $L$. Neutron stars obtained with Gogny forces have maximum masses below $1.74M_\odot$ and relatively small moments of inertia. The crustal mass and moment of inertia are evaluated and comparisons are made with the constraints from observed glitches in pulsars.

nucl-th↗
arXiv2017

Interdependence of different symmetry energy elements

Relations between the nuclear symmetry energy coefficient and its density derivatives are derived. The relations hold for a class of interactions with quadratic momentum dependence and a power-law density dependence. The structural connection between the different symmetry energy elements as obtained seems to be followed by almost all reasonable nuclear energy density functionals, both relativistic and non-relativistic, suggesting a universality in the correlation structure. This, coupled with known values of some well-accepted constants related to nuclear matter, helps in constraining values of different density derivatives of the nuclear symmetry energy shedding light on the isovector part of the nuclear interaction.

nucl-th↗
arXiv2017

Semiclassical approximation to the Hartree-Fock method in finite nuclei

In this paper we review the semiclassical extended Thomas-Fermi theory for describing the ground-state properties of nuclei. The binding energies calculated in this approach do not contain shell effects and, in this sense, they are analogous to those obtained from the mass formula. We discuss some techniques for incorporating the shell effects which are missing in the semiclassical calculation, such as the so-called expectation value method and the Kohn-Sham scheme. We present numerical applications for effective zero-range Skyrme forces and finite-range Gogny forces.

nucl-th↗