arXiv subjects

S. P. Maydanyuk

Publications and source records attributed to S. P. Maydanyuk.

8 recordsLinked to original sources

arXiv2026

Rotating neutron stars within the macroscopic effective-surface approximation

The macroscopic model for a neutron star (NS) as a finite perfect fluid at the equilibrium is extended to rotating systems by incorporating the linear perturbation expansion over a small frequency $ω$ near Schwarzschild outer-inner gravitational metric within the effective-surface (ES) approach. The NS angular momentum $I$ and moment of inertia (MI) for a slow stationary azimuthal rotation around the symmetry axis are calculated by using the Kerr metric approach in spherical coordinates, and compared with Boyer-Lindquist (outer) and Hogan (inner) metric results. The volume and gradient-surface terms of the macroscopic NS energy density $\mathcal{E}(ρ)$ (Equation of State) are taken into account at the leading order of the leptodermic parameter $a/R \ll 1$, where $a$ is the ES crust thickness and $R$ is the NS effective radius. The analytical macroscopic NS MI expressions, $Θ= \mathrm{d}I/\mathrm{d}ω= \tildeΘ/(1-\mathcal{T}_{tφ})$, have been obtained in terms of the statistically averaged MI, $\tildeΘ$, and its time and azimuthal-angle $t,φ$ correlation, $\mathcal{T}_{tφ}$, as sums of the volume and surface components. The MI $Θ$ is changed significantly as function of the effective radius $R$ because of a strong gravity. We found the additional constraint for the NS radius to smaller accessible ranges which is due mainly to the $t,φ$ correlations and surface contributions. The adiabaticity conditions for applicability of the linear perturbation theory is carried out for several neutron stars with a strong gravity and relatively large rotation periods.

gr-qc↗

arXiv2026

Macroscopic approaches to rotating neutron stars

The macroscopic model for a neutron star (NS) as a perfect liquid drop at equilibrium is extended to rotating systems with a small frequency $ω$ within the effective-surface (ES) approach. The gradient surface terms of the NS energy density $\cal{E}(ρ)$ in the Equation of State are taken into account along with the volume components at the leading order over the leptodermic parameter $a/R << 1$, where $a$ is the ES crust thickness and $R$ is the mean NS radius. The macroscopic NS angular momentum at small frequencies $ω$ is used for calculations of the adiabatic moment of inertia (MI) within the Kerr metric approach in the outer Boyer-Lindquist and inner Hogan coordinate forms. The NS MI, $Θ=\tildeΘ/(1-\cal{G}_{tφ})$, was obtained in terms of the statistically averaged MI, $\tildeΘ$, and its time and azimuthal-angle correlation, $\cal{G}_{tφ}$, as the sums of volume and surface components. The MI $Θ$ depends dramatically on the effective radius $R$ due to strong gravitation and surface effects. We found significant additional rotational constraints on the radius $R$ due to the correlation term $\cal{G}_{tφ}$ and surface contributions. With these contributions, the adiabaticity condition is better fulfilled for a stronger gravitation in many well-known neutron stars.

astro-ph.HE↗

arXiv2025

Leptodermic corrections to the TOV equations and nuclear astrophysics within the effective surface approximation

The macroscopic model for a neutron star (NS) as a liquid drop at the equilibrium is used to extend the Tolman-Oppenheimer-Volkoff (TOV) equations taking into account the gradient terms responsible for the system surface. The parameters of the Schwarzschild metric in the spherical case are found with these surface corrections to the known leading (zero) order of the leptodermic approximation $a/R<<1$, where $a$ is the NS effective-surface (ES) thickness, and $R$ is the effective NS radius. The energy density $\mathcal{E}$ is considered in a general form including the functions of the particle number density and of its gradient terms. The macroscopic gravitational component $Φ(ρ)$ of the energy density is taken into account in the simplest form as expansion in powers of $ρ-\overlineρ $, where $\overlineρ$ is the saturation density, up to second order, in terms of its contributions to the separation particle energy and incompressibility. Density distributions $ρ$ across the NS ES in the normal direction to the ES, which are derived in the simple analytical form at the same leading approximation, was used for the derivation of the modified TOV (MTOV) equations by accounting for their NS surface corrections. The MTOV equations are analytically solved at first order and the results are compared with the standard TOV approach of the zero order.

gr-qc↗

arXiv2025

Neutron stars as a dense liquid drop at equilibrium within the effective surface approximation

The macroscopic model is formulated for a neutron star (NS) as a perfect liquid drop at the equilibrium. We use the leptodermic approximation $a/R\ll 1$, where $a$ is the crust thickness of the effective NS surface (ES), and $R$ is the mean radius of the ES curvature. Within the approximate Schwarzschild metric solution to the general relativity theory equations for the spherically symmetric systems, the macroscopic gravitation is taken into account in terms of the total separation particle energy and incompressibility. Density distribution $ρ$ across the ES in the normal direction to the ES was obtained analytically for a general form of the energy density $\mathcal{E}(ρ)$. For the typical crust thickness, and effective radius, one finds the leading expression for the density $ρ$. NS masses are analytically calculated as a sum of the volume and surface terms, taking into account the radial curvature of the metric space, in reasonable agreement with the recently measured masses for several neutron stars. We derive the simple macroscopic equation of state (EoS) with the surface correction. The analytical and numerical solutions to Tolman-Oppenheimer-Volkoff equations for the pressure are in good agreement with the volume part of our EoS.

nucl-th↗

arXiv2025

Manifestation of quark effects in nuclei via bremsstrahlung analysis in the proton-nucleus scattering

\textbf{Background} (1) The incoherent emission of photons is dominant comparing to coherent one in proton-nucleus scattering. The incoherent bremsstrahlung is very sensitive to the magnetic moments of nucleons in nuclei. (2) According to the quark-meson coupling (QMC) model, the nucleon magnetic moments in nuclei are enhanced relative to those in vacuum, originating from the quark structure of nucleons. \textbf{Purpose} Investigate possibilities of observing quark effects in nuclei by the analysis of bremsstrahlung in nuclear reactions. \textbf{Methods} Analyse the bremsstrahlung cross sections with established model in proton-nucleus scattering, by extending with inclusion of in-medium modified nucleon magnetic moments in nuclei by the QMC model. \textbf{Results} (1) After calibrating the model without the quark effects for experimental data (TAPS Collaboration data for $p + \isotope[197]{Au}$), we calculate the cross sections and observe the slight difference between the spectra for models with and without quark effects. Such result is found for the first time, confirming possibilities of observing the quark effects in the spectra of bremsstrahlung. (2) As found, quark effects are not enough to be observed in middle and heavy nuclei, as they have dominant incoherent contributions. (3) \isotope[18]{C} has minimal incoherent contribution concerning other carbon isotopes, where the quark effects should be minimal. In ratios between the spectra for \isotope[18]{C} and \isotope[12]{C} with and without the quark effects the difference is clearly observed. \textbf{Conclusions} We establish the new physical observable for the quark effects in nuclei in the bremsstrahlung accompanied in the nuclear reactions, which can be measured. The present suggestion is for the first time in both theoretically and experimentally to study the quark effects in nuclei via the bremsstrahlung.

nucl-th↗

arXiv2024

Study of structure of deuteron from analysis of bremsstrahlung emission in proton-deuteron scattering in cluster models

Purpose: In this paper we investigated emission of bremsstrahlung photons in the scattering of protons off deuterons within the microscopic cluster models in a wide region of the beam energy from low energies up to 1.5 GeV. Methods: Three-cluster model of bremsstrahlung is constructed for such a reaction. Formalism of the model includes form factor of deuteron which characterizes dependence of bremsstrahlung cross sections on structure of deuteron. This gives possibility to investigate the structure of nuclei from analysis of bremsstrahlung cross sections. Results: We studied dependence of the bremsstrahlung cross section on the structure of deuteron. We use three different shapes of the deuteron wave functions. Besides, we also calculate the cross section by neglecting internal structure of deuteron. Analysis of dependence of the cross section on such a parameter shows the following. (1) At beam energies 145 and 195 MeV used in experiments bremsstrahlung cross section is not sensitive visibly on variations of the shape of the deuteron wave functions. (2) Stable difference between cross sections calculated with and without internal structure of deuteron is observed at higher energy of beam (larger 500 MeV). (3) The spectrum is increased as we pass from structureless deuteron (the oscillator length $b=0$) to the deuteron discribed by the shell-model wave function (the realistic oscillator length) inside the full energy region of the emitted photons. Conclusion: Our cluster model is a suitable tool to study the structure of deuteron with high enough precision from bremsstrahlung analysis. We propose new experiments for such an investigation.

nucl-th↗

arXiv2023

Systematic study of bremsstrahlung emission in reactions with light nuclei in cluster models

A new model of bremsstrahlung emission in the scattering of light nuclei is constructed with main focus on strict cluster formulation of nuclear processes. Analysis is performed in frameworks of the folding approximation of the formalism with participation of $s$-nuclei. Reactions $p$ +$^4$He, $^2$D + $^4$He, $^3$H + $^4$He, $^3$He + $^4$He are included to analysis. Systematic analysis of properties of emission of bremsstrahlung photons in the wide region of kinetic energy of relative motion of two nuclei from 7 to 1000~MeV is performed. Influence of the oscillator length on the calculated spectra of bremsstrahlung emission is analyzed. On the example of $^3$H + $^4$He, dependence of the bremsstrahlung spectra on parameters of nuclear component of interacting potential is established (at first time for the light nuclei). Experimental bremsstrahlung data for the proton-deuteron scattering and proton-$α$-particle scattering are analyzed on the basis of this model.

nucl-th↗

arXiv2013

Shear and rotation in Chaplygin cosmology

We study the effect of shear and rotation on results previously obtained dealing with the application of the spherical collapse model (SCM) to generalized Chaplygin gas (gCg) dominated universes. The system is composed of baryons and gCg and the collapse is studied for different values of the parameter $α$ of the gCg. We show that the joint effect of shear and rotation is that of slowing down the collapse with respect to the simple SCM. This result is of utmost importance for the so-called unified dark matter models, since the described slow down in the growth of density perturbation can solve one of the main problems of the quoted models, namely the instability described in previous papers [e.g., H. B. Sandvik {\it et al.}, Phys. Rev. D {\bf 69}, 123524 (2004)] at the linear perturbation level.

astro-ph.CO↗