arXiv subjects

S. K. Samaddar

Publications and source records attributed to S. K. Samaddar.

At least 19 recordsLinked to original sources

arXiv2020

Constraining nuclear matter parameters from correlation systematics:a mean-field perspective

The nuclear matter parameters define the nuclear equation of state (EoS), they appear as coefficients of expansion around the saturation density of symmetric and asymmetric nuclear matter. We review their correlations with several properties of finite nuclei and of neutron stars within mean-field frameworks. The lower order nuclear matter parameters such as the binding energy per nucleon, incompressibility and the symmetry energy coefficients are found to be constrained in narrow limits through their strong ties with selective properties of finite nuclei. From the correlations of nuclear matter parameters with neutron star observables, we further review how precision knowledge of the radii and tidal deformability of neutron stars in the mass range $1 - 2 M_\odot$ may help cast them in narrower bounds. The higher order parameters such as the density slope and the curvature of the symmetry energy or the skewness of the symmetric nuclear matter EoS are, however, plagued with larger uncertainty. From inter-correlation of these higher order nuclear matter parameters with lower order ones, we explore how they can be brought to more harmonious bounds.

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arXiv2019

Tides in merging neutron stars: Consistency of the GW170817 event with experimental data on finite nuclei

The agreement of the nuclear equation of state (EoS) deduced from the GW170817 based tidal deformability with the one obtained from empirical data on microscopic nuclei is examined. It is found that suitably chosen experimental data on isoscalar and isovector modes of nuclear excitations together with the observed maximum neutron star mass constrain the EoS which displays a very good congruence with the GW170817 inspired one. The giant resonances in nuclei are found to be instrumental in limiting the tidal deformability parameter and the radius of neutron star in somewhat narrower bounds. At the 1$σ$ level, the values of the canonical tidal deformability $Λ_{1.4}$ and the neutron star radius $R_{1.4}$ come out to be $267\pm144$ and $11.6\pm1.0$ km, respectively.

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arXiv2018

The nucleon effective mass and its isovector splitting

Using an energy density functional (EDF) based on the thermodynamic Gibbs-Duhem relation, found equivalent to the standard Skyrme EDF for infinite nuclear matter, it is demonstrated that the parameters of this EDF are not uniquely determined from the fit of the empirical and theoretical data related to nuclear matter. This prevents an unambiguous determination of the nucleon effective mass ($\frac{m_0^*}{m}$) and its isovector splitting ($Δm_0^*$). Complementary information from dipole polarizability of atomic nuclei helps in removing this ambiguity and plausible values of $\frac{m_0^*}{m}$ and $Δm_0^*$ can be arrived at. Presently considered fit data on infinite nuclear matter and dipole polarizability of finite nuclei yield $\frac{m_0^*}{m} =0.68 \pm 0.04 $ and $Δm_0^* =(-0.20 \pm 0.09)δ$. This EDF is consistent with the constraint on the maximum mass of the neutron star.

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arXiv2018

Correlations among symmetry energy elements in Skyrme models

Motivated by the interrelationships found between the various symmetry energy elements of the energy density functionals (EDF) based on the Skyrme forces, possible correlations among them are explored. A total of 237 Skyrme EDFs are used for this purpose. As some of these EDFs yield values of a few nuclear observables far off from the present acceptable range, studies are done also with a subset of 162 EDFs that comply with a conservative set of constraints on the values of nuclear matter incompressibility coefficient, effective mass of the nucleon and the isovector splitting of effective nucleon masses to see the enhancement of the correlation strength, if any. The curvature parameter $K^0_{sym}$ and the skewness parameter $Q^0_{sym}$ of the symmetry energy are found to be very well correlated with the linear combination of the symmetry energy coefficient and its density derivative $L_0$ . The isovector splitting of the effective nucleon mass, however, displays a somewhat meaningful correlation with a linear combination of the symmetry energy, its slope and its curvature parameter.

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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.

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arXiv2017

Limiting symmetry energy elements from empirical evidence

In the framework of an equation of state (EoS) constructed from a momentum and density-dependent finite-range two-body effective interaction, the quantitative magnitudes of the different symmetry elements of infinite nuclear matter are explored. The parameters of this interaction are determined from well-accepted characteristic constants associated with homogeneous nuclear matter. The symmetry energy coefficient $a_2$, its density slope $L_0$, the symmetry incompressibility $K_δ$ as well as the density dependent incompressibility $K(ρ)$ evaluated with this EoS are seen to be in good harmony with those obtained from other diverse perspectives. The higher order symmetry energy coefficients $a_4,~a_6$ etc are seen to be not very significant in the domain of densities relevant to finite nuclei, but gradually build up at supra-normal densities. The analysis carried with a Skyrme-inspired energy density functional obtained with the same input values for the empirical bulk data associated with nuclear matter yields nearly the same results.

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arXiv2016

Sensitivity of elements of the symmetry energy of nuclear matter to the properties of neutron-rich systems

The sensitivity of nuclear symmetry energy elements at the saturation density to the binding energies of ultra neutron-rich nuclei (neutron to proton ratio $\sim$ 2) and the maximum mass of neutron star is explored within a relativistic mean field model. Values of the interaction parameters governing the isovector strengths and the symmetry elements are determined in tighter bounds. Assessments based on the sensitivity matrix reveal that the properties of extreme neutron-rich systems play a predominant role in narrowing down the uncertainties in the various symmetry energy parameters. The calculations are extended over a wide range of nuclear matter density and the results are discussed.

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arXiv2015

Reassessing nuclear matter incompressibility and its density dependence

Experimental giant monopole resonance energies are now known to constrain nuclear incompressibility of symmetric nuclear matter $K$ and its density slope $M$ at a particular value of sub-saturation density, the crossing density $ρ_c$. Consistent with these constraints, we propose a reasonable way to construct a plausible equation of state of symmetric nuclear matter in a broad density region around the saturation density $ρ_0$. Help of two additional empirical inputs, the value of $ρ_0$ and that of the energy per nucleon $e(ρ_0)$ are needed. The value of $K(ρ_0)$ comes out to be $211.9\pm 24.5$ MeV.

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arXiv2014

Equation of state of nuclear matter from empirical constraints

From empirically determined values of some of the characteristic constants associated with homogeneous nuclear matter at saturation and sub-saturation densities, within the framework of a Skyrme-inspired energy density functional, we construct an equation of state (EoS) of nuclear matter.This EoS is then used to predict values of density slope parameters of symmetry energy $L(ρ)$, isoscalar incompressibility $K(ρ)$ and a few related quantities. The close consonance of our predicted values with the currently available ones for the density dependence of symmetry energy and incompressibility gleaned from diverse approaches offers the possibility that our method may help in settling their values in tighter bounds. Extrapolation of our EoS at supranormal densities shows that it is in good harmony with the one extracted from experimental data.

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arXiv2014

Thermal properties of the nuclear surface

The thermal evolution of a few thermodynamic properties of the nuclear surface like its thermodynamic potential energy, entropy and the symmetry free energy are examined for both semi-infinite nuclear matter and finite nuclei. The Thomas-Fermi model is employed. Three Skyrme interactions, namely, SkM$^*$, SLy4 and SK255 are used for the calculations to gauge the dependence of the nuclear surface properties on the energy density functionals. For finite nuclei, the surface observables are computed from a global liquid-drop inspired fit of the energies and free energies of a host of nuclei covering the entire periodic table. The hot nuclear system is modelled in a subtracted Thomas-Fermi framework. Compared to semi-infinite nuclear matter, substantial changes in the surface symmetry energy of finite nuclei are indicated; surface thermodynamic potential energies for the two systems are, however, not too different. Analytic expressions to fit the temperature and asymmetry dependence of the surface thermodynamic potential of semi-infinite nuclear matter and the temperature dependence of the surface free energy of finite nuclei are given.

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arXiv2013

Symmetry energy of warm nuclear systems

The temperature dependence of the symmetry energy and symmetry free energy coefficients of infinite nuclear matter and of finite nuclei is investigated. For infinite matter, both these coefficients are found to have a weaker dependence on temperature at densities close to saturation; at low but homogeneous densities, the temperature dependence becomes stronger. For finite systems, different definitions of symmetry energy coefficients are encountered in the literature yielding different values. A resolution to this problem is suggested from a global liquid-drop-inspired fit of the energies and free energies of a host of nuclei covering the entire periodic table. The hot nucleus is modeled in a subtracted finite-temperature-Thomas-Fermi framework, with dynamical surface phonon coupling to nucleonic motion plugged in. Contrary to infinite nuclear matter, a substantial change in the symmetry energy coefficients is observed for finite nuclei with temperature.

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arXiv2013

Constraining the density dependence of symmetry energy from nuclear masses

Empirically determined values of the nuclear volume and surface symmetry energy coefficients from nuclear masses are expressed in terms of density distributions of nucleons in heavy nuclei in the local density approximation. This is then used to extract the value of the symmetry energy slope parameter $L$. The density distributions in both spherical and well deformed nuclei calculated within microscopic framework with different energy density functionals give $L = 59.0 \pm 13.0$ MeV. Application of the method also helps in a precision determination of the neutron skin thickness of nuclei that are difficult to measure accurately.

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arXiv2012

Determining the density content of symmetry energy and neutron skin: an empirical approach

The density dependence of nuclear symmetry energy remains poorly constrained. Starting from precise empirical values of the nuclear volume and surface symmetry energy coefficients and the nuclear saturation density, we show how in the ambit of microscopic calculations with different energy density functionals, the value of the symmetry energy slope parameter $L$ alongwith that for neutron skin can be put in tighter bounds. The value of $L$ is found to be $L$= 64$\pm $5 MeV. For $^{208}$Pb, the neutron skin thickness comes out to be 0.188 $\pm $0.014 fm. Knowing $L$, the method can be applied to predict neutron skins of other nuclei.

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arXiv2012

Temperature dependence of volume and surface symmetry energy coefficients of nucle

The thermal evolution of the energies and free energies of a set of spherical and near-spherical nuclei spanning the whole periodic table are calculated in the subtracted finite-temperature Thomas- Fermi framework with the zero-range Skyrme-type KDE0 and the finite-range modified Seyler-Blanchard interaction. The calculated energies are subjected to a global fit in the spirit of the liquid-drop model. The extracted parameters in this model reflect the temperature dependence of the volume symmetry and surface symmetry coefficients of finite nuclei, in addition to that of the volume and surface energy coefficients. The temperature dependence of the surface symmetry energy is found to be very substantial whereas that of the volume symmetry energy turns out to be comparatively mild.

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arXiv2012

The effects of medium on nuclear properties in multifragmentation

In multifragmentation of hot nuclear matter, properties of fragments embedded in a soup of nucleonic gas and other fragments should be modified as compared with isolated nuclei. Such modifications are studied within a simple model where only nucleons and one kind of heavy nuclei are considered. The interaction between different species is described with a momentum-dependent two-body potential whose parameters are fitted to reproduce properties of cold isolated nuclei. The internal energy of heavy fragments is parametrized according to a liquid-drop model with density and temperature dependent parameters. Calculations are carried out for several subnuclear densities and moderate temperatures, for isospin-symmetric and asymmetric systems. We find that the fragments get stretched due to interactions with the medium and their binding energies decrease with increasing temperature and density of nuclear matter.

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arXiv2012

Temperature dependence of symmetry energy of finite nuclei

The temperature dependence of the symmetry energy and the symmetry free energy coefficients of atomic nuclei is investigated in a finite temperature Thomas-Fermi framework employing the subtraction procedure. A substantial decrement in the symmetry energy coefficient is obtained for finite systems,contrary to those seen for infinite nuclear matter at normal and somewhat subnormal densities. The effect of the coupling of the surface phonons to the nucleonic motion is also considered; this is found to decrease the symmetry energies somewhat at low temperatures.

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arXiv2011

Warm alpha-nucleon matter

The properties of warm dilute alpha-nucleon matter are studied in a variational approach in the Thomas-Fermi approximation starting from an effective two-body nucleon-nucleon interaction. The equation of state, symmetry energy, incompressibility of the said matter as well as the alpha fraction are in consonance with those evaluated from the virial approach that sets a bench-mark for such calculations at low densities.

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arXiv2010

Anatomy of symmetry energy of dilute nuclear matter

The symmetry energy coefficients of dilute clusterized nuclear matter are evaluated in the $S$-matrix framework. Employing a few different definitions commonly used in the literature for uniform nuclear matter, it is seen that the different definitions lead to perceptibly different results for the symmetry coefficients for dilute nuclear matter. They are found to be higher compared to those obtained for uniform matter in the low density domain. The calculated results are in reasonable consonance with those extracted recently from experimental data.

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