arXiv subjects

T. R. Routray

Publications and source records attributed to T. R. Routray.

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+$μ$ composition in $β$-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

Constraining Nuclear Symmetry Energy parameters from Neutron skin thickness of $^{48}$Ca

In the present work, we use a finite range effective interaction to calculate the neutron skin thickness in $^{48}$Ca and correlate these quantities with the parameters of nuclear symmetry energy. Available experimental data on the neutron skin thickness in $^{48}$Ca are used to deduce information on the density slope parameter and the curvature symmetry parameter of the nuclear symmetry energy at saturation and at subsaturation densities. We obtained the constraints such as $54.5\leq L(ρ_0) \leq 97.5$ MeV and $47.3\leq L(ρ_c) \leq 57.1$ MeV for the density slope parameter. The constraints on the curvature symmetry energy parameter are obtained as $-170.7\leq K_{sym}(ρ_0) \leq -43.4$ MeV and $-80.8\leq K_{sym}(ρ_c) \leq 23.8$ MeV. A linear relation between the neutron skin thickness in $^{48}$Ca and in $^{2088}$Pb is obtained.

nucl-th↗

arXiv2020

Nuclear Symmetry Energy and Neutron Skin Thickness of $^{208}Pb $ using a finite range effective interaction

We use a finite range simple effective interaction to construct nuclear equations of state for the study of the density dependence of the nuclear symmetry energy. The EoSs provide good descriptions of the nuclear symmetry energy at a subsaturation density $ρ_c=0.11$ fm$^{-3}$ and at a density around two times the saturation density $ρ_0$. We obtain a correlation between the neutron skin thickness in $^{208}$Pb and the density slope parameter at the subsaturation density. A linear relation is obtained between the neutron skin thickness and the parameter $β^{\prime}=\frac{L(ρ_c)}{3E_s(ρ_0)}$, where $E_s(ρ_0)$ and $L(ρ_c)$ are respectively the nuclear symmetry energy at saturation density and the density slope parameter at the subsaturation density.

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↗

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

Half lives of proton emitters with KDE0v1 Skyrme interaction

The half-lives of proton radioactivity of proton emitters are investigated theoretically by using KDE0v1 Skyrme interaction. The total barrier potential in the proton radioactive nuclei is calculated as the sum of the nuclear, Coulomb and centrifugal contributions. The Hartree-Fock nuclear density distributions is used in calculating the nuclear as well as the Coulomb interaction potentials. The quantum mechanical tunneling probability is calculated within the WKB approximation. These calculations provide reasonable estimates for the observed proton radioactivity lifetimes.

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

Deformation properties with a finite range simple effective interaction

Deformed and spherical even-even nuclei are studied using a finite range simple effective interaction within the Hartree-Fock-Bogoliubov mean field approach. Different parameter sets of the interaction, corresponding to different incompressibility, are constructed by varying the exponent gamma of the density in the traditional density-dependent term. Ten of the twelve parameters of these interactions are determined from properties of asymmetric nuclear matter and spin polarized pure neutron matter. The two remaining parameters are fitted to reproduce the experimental binding energies known in 620 even-even nuclei using several variants of the rotational energy correction. The rms deviations for the binding energy depend on the value of gamma and the way the rotational energy correction is treated but they can be as low as 1.56 MeV, a value competitive with other renowned effective interactions of Skyrme and Gogny type. Charge radii are compared to the experimental values of 313 even-even nuclei and the rms deviation is again comparable and even superior to the one of popular Skyrme and Gogny forces. Emphasis is given to the deformation properties predicted with these interactions by analyzing the Potential Energy Surfaces for several well deformed nuclei and the fission barriers of some nuclei. Comparison of the results with the experimental information, where available, as well as with the results of the Gogny D1S force shows satisfactory agreement.

nucl-th↗

arXiv2016

Inner crust of neutron stars with mass-fitted Skyrme interaction

The mass, radius and crustal fraction of moment of inertia in neutron stars are calculated using $β$-equilibrated nuclear matter obtained from Skyrme effective interaction. The transition density, pressure and proton fraction at the inner edge separating the liquid core from the solid crust of the neutron stars are determined from the thermodynamic stability conditions using the KDE0v1 set. The neutron star masses obtained by solving the Tolman-Oppenheimer-Volkoff equations using neutron star matter obtained from this set is able to describe highly massive compact stars $\sim$2$M_{\odot}$. The crustal fraction of the moment of inertia can be extracted from studying pulsar glitches. This fraction is highly dependent on the core-crust transition pressure and corresponding density. These results for pressure and density at core-crust transition together with the observed minimum crustal fraction of the total moment of inertia provide a limit for the radius of the Vela pulsar:$R\geq$ 3.69+3.44 M/$M_{\odot}$. Present calculations suggest that the crustal fraction of the total moment of inertia can be at most 3.6% due to crustal entrainment caused by Bragg reflection of unbound neutrons by lattice ions.

nucl-th↗

arXiv2016

Exact versus Taylor-expanded energy density in the study of the neutron star crust-core transition

The importance of the fourth and higher order terms in the Taylor series expansion of the energy of the isospin asymmetric nuclear matter in the study of the neutron star crust-core phase transition is investigated using the finite range simple effective interaction. Analytic expressions for the evaluation of the second and fourth order derivative terms in the Taylor series expansion for any general finite range interaction of Yukawa, exponential or Gaussian form have been obtained. The effect of the nuclear matter incompressibility, symmetry energy and slope parameters on the predictions for the crust-core transition density is examined. The crustal moment of inertia is calculated and the prediction for the radius of the Vela pulsar is analyzed using different equations of state.

nucl-th↗

arXiv2015

Anisotropic Cosmological Model with Variable G and Lambda

Anisotropic Bianchi-III cosmological model is investigated with variable gravitational and cosmological constants in the framework of Einstein's general relativity. The shear scalar is considered to be proportional to the expansion scalar. The dynamics of the anisotropic universe with variable G and Lambda are discussed. Without assuming any specific forms for Lambda and the metric potentials, we have tried to extract the time variation of G and Lambda from the anisotropic model. The extracted G and Lambda are in conformity with the present day observation. Basing upon the observational limits, the behaviour and range of the effective equation of state parameter are discussed.

gr-qc↗

arXiv2015

Study of spin polarized nuclear matter and finite nuclei with finite range simple effective interaction

The properties of spin polarized pure neutron matter and symmetric nuclear matter are studied using the finite range simple effective interaction, upon its parametrization revisited. Out of the total twelve parameters involved, we now determine ten of them from nuclear matter, against the nine parameters in our earlier calculation, as required in order to have predictions in both spin polarized nuclear matter and finite nuclei in unique manner being free from uncertainty found using the earlier parametrization. The information on the effective mass splitting in polarized neutron matter of the microscopic calculations is used to constrain the one more parameter, that was earlier determined from finite nucleus, and in doing so the quality of the description of finite nuclei is not compromised. The interaction with the new set of parameters is used to study the possibilities of ferromagnetic and antiferromagnetic transitions in completely polarized symmetric nuclear matter. Emphasis is given to analyze the results analytically, as far as possible, to elucidate the role of the interaction parameters involved in the predictions.

nucl-th↗

arXiv2013

Simple effective interaction: Infinite nuclear matter and finite nuclei

The mean field properties and equation of state for asymmetric nuclear matter are studied by using a simple effective interaction which has a single finite range Gaussian term. The study of finite nuclei with this effective interaction is done by means of constructing a quasilocal energy density functional for which the single particle equations take the form of Skryme-Hartree-Fock equations. The predictions of binding energies and charge radii of spherical nuclei are found to be compatible with the results of standard models as well as experimental data.

nucl-th↗

arXiv2012

An effective Nuclear Model: from Nuclear Matter to Finite Nuclei

The momentum and density dependence of mean fields in symmetric and asymmetric nuclear matter are analysed using the simple density dependent finite range effective interaction containing a single Gaussian term alongwith the zero-range terms. Within the formalism developed, it is possible to reproduce the various diverging predictions on the momentum and density dependence of isovector part of the mean field in asymmetric matter. The finite nucleus calculation is formulated for the simple Gaussian interaction in the framework of quasilocal density functional theory. The prediction of energies and charge radii of the interaction for the spherical nuclei compares well with the results of other effective theories.

nucl-th↗

arXiv2012

Proton radioactivity half lives with Skyrme interactions

The potential barrier impeding the spontaneous emission of protons in the proton radioactive nuclei is calculated as the sum of nuclear, Coulomb and centrifugal contributions. The nuclear part of the proton-nucleus interaction potential is obtained in the energy density formalism using Skyrme effective interaction that results into a simple algebraic expression. The half-lives of the proton emitters are calculated for the different Skyrme sets within the improved WKB framework. The results are found to be in reasonable agreement with the earlier results obtained for more complicated calculations involving finite range interactions.

nucl-th↗