arXiv subjects

Athul Kunjipurayil

Publications and source records attributed to Athul Kunjipurayil.

4 recordsLinked to original sources

arXiv2026

Thermodynamic versus Dynamical Description of the Neutron-Star Crust-Core Instability: Implications for Crustal Observables

We investigate the crust-core transition in neutron stars using both thermodynamic and dynamical descriptions of the instability. In the thermodynamic approach, the transition is identified through the vanishing of a generalized incompressibility coefficient signaling the onset of a bulk spinodal instability. In contrast, the dynamical approach based on the relativistic random-phase approximation (RPA) incorporates Coulomb screening and finite-size effects that determine the instability at finite wavelength. Using a family of covariant energy density functionals spanning a broad range of symmetry-energy slopes, we show that the dynamical treatment systematically predicts lower transition densities and pressures compared to the thermodynamic approach. We further demonstrate that the RPA instability develops at a characteristic length scale set by the competition among bulk, Coulomb, and surface effects. Most importantly, we show that these differences propagate directly into neutron-star observables. Because the thermodynamic approach predicts larger transition pressures, it generates thicker crusts and significantly larger crustal fractions of the stellar moment of inertia than the dynamical-RPA framework -- with important implications for the interpretation of pulsar glitches and other crust-sensitive neutron-star observables.

nucl-th↗

arXiv2025

Elucidating the role of the surface energy in density functional theory

The saturation of symmetric nuclear matter -- reflected in the nearly constant interior density of heavy nuclei -- is a defining property of nuclear matter. Modern relativistic energy density functionals (EDFs) calibrated exclusively to the properties of finite nuclei, make robust predictions with quantified uncertainties about the bulk properties of symmetric nuclear matter in the vicinity of the saturation density. Following the same fitting protocol, nonrelativistic Skyrme EDFs systematically predict higher saturation densities than their relativistic counterparts. To investigate this tension in the bulk limit, we study the ground-state properties of hypothetical symmetric macroscopic nuclei containing thousands of nucleons. Using both relativistic and non-relativistic EDF frameworks, we extract the corresponding liquid-drop parameters. We find a clear correlation between the volume and surface energy coefficients: Skyrme models, which saturate at higher densities, develop softer and more diffuse surfaces with lower surface energies, whereas relativistic EDFs, which saturate at lower densities, produce more defined and less diffuse surfaces with higher surface energies. This compensating behavior allows both classes of models to reproduce empirical nuclear radii despite their distinct saturation properties. Our analysis suggests that the apparent disparity in saturation densities arises from the intrinsic balance among saturation density, bulk binding energy, and surface tension, rather than from the fitting protocol.

nucl-th↗

arXiv2025

Role of the isovector spin-orbit potential in mitigating the CREX-PREX dilemma

Pioneering electroweak measurements of the neutron skin thickness in lead-208 and calcium-48 are challenging our understanding of nuclear dynamics. Many theoretical models suggest that the slope of the symmetry energy controls the development of a neutron skin in neutron-rich nuclei. This led to the expectation that if lead-208 exhibits a large neutron skin, calcium-48 should as well. Given that the PREX collaboration reported a relatively thick neutron skin in lead, we anticipated that calcium would also have a significant neutron skin. Instead, the CREX collaboration reported a thin neutron skin in calcium. Although many suggestions have been proposed, the ``CREX-PREX dilemma" remains unsolved. Recently, an intriguing scenario has emerged, suggesting that an enhanced isovector spin-orbit interaction could simultaneously account for both results. Following this approach, we performed relativistic mean-field calculations with an increased isovector spin-orbit potential. Our findings indicate that while this modification significantly affects the structure of calcium-48, it has only a marginal impact on lead-208, thereby bringing the results into better agreement with experiment. However, the strong enhancement required to mitigate the CREX-PREX dilemma destroys the agreement with a successful spin-orbit phenomenology, primarily by modifying the well-known ordering of spin-orbit partners.

nucl-th↗

arXiv2022

Impact of the equation of state on $f$- and $p$- mode oscillations of neutron stars

We investigate the impact of the neutron-star matter equation of state on the $f$- and $p_1$-mode oscillations of neutron stars obtained within the Cowling approximation and linearized general relativity. The $f$- and $p_1$-mode oscillation frequencies, and their damping times are calculated using representative sets of Skyrme Hartree-Fock and relativistic mean-field models, all of which reproduce nuclear systematics and support $2M_\odot$ neutron stars. Our study shows strong correlations between the frequencies of $f$- and $p_1$-modes and their damping times with the pressure of $β$-equilibrated matter at densities equal to or slightly higher than the nuclear saturation density $ρ_0$. Such correlations are found to be almost independent of the composition of the stars. The frequency of the $p_1$-mode of $1.4M_\odot$ star is strongly correlated with the slope of the symmetry energy $L_0$ and $β$-equilibrated pressure at density $ρ_0$. Compared to GR calculations, the error in the Cowling approximation for the $f$-mode is about 30\% for neutron stars of low mass, whereas it decreases with increasing mass. The accuracy of the $p_1$-mode is better than 15\% for neutron stars of maximum mass, and improves for lower masses and higher number of radial nodes.

nucl-th↗