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Sergiy V. Lukyanov

Publications and source records attributed to Sergiy V. Lukyanov.

5 recordsLinked to original sources
arXiv2026

Dissipative properties of a Fermi system within the diffusion approximation of kinetic theory

The dissipative properties of a Fermi system are studied within the diffusion approximation of kinetic theory for a model of a spherical atomic nucleus. An analytical solution of the nonlinear diffusion equation in energy space with constant kinetic coefficients is used to show that the distribution function asymptotically approaches the equilibrium Fermi distribution. It is found that the deviation from equilibrium at finite times decays with an effective relaxation time of $τ_\mathrm{eff}\approx 1.0\times10^{-23}$ s, whereas the asymptotic regime is characterized by an exponential decay with a relaxation time of $τ_\text{eq}\approx 3\,τ_\text{eff}$. These results explain the difference between the relaxation times extracted from integral characteristics of the relaxation process and from the asymptotic long-time evolution.

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arXiv2026

Equilibrium state of a Fermi system in the diffusion approximation of kinetic theory

A consistent transformation from momentum space to energy space is performed for the diffusion equation within kinetic theory, with particle-number conservation explicitly preserved. Under the assumption of a constant single-particle level density, the equation reduces to a one-dimensional diffusion equation in energy space with consistent kinetic coefficients. The equivalence of the definitions of the equilibrium temperature in momentum space and in energy space is demonstrated. It is established that the inclusion of the energy dependence of the kinetic coefficients leads to an energy-dependent equilibrium temperature and a modification of the distribution function. The obtained results may be used to analyze relaxation processes in atomic nuclei and nonequilibrium dynamics of Fermi systems.

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arXiv2026

Relaxation of a single-particle excitation in a Fermi system within the diffusion approximation of kinetic theory

The time evolution of the Wigner distribution function for a single-particle excitation in a Fermi system was studied within the framework of the diffusion approximation of kinetic theory by numerically solving a nonlinear diffusion equation with constant kinetic coefficients. A method was proposed to separate the dissipative processes into contributions from the relaxation of the single-particle excitation and from the relaxation of the nuclear core, with a distinct relaxation time introduced for each process. The influence of the diffusion and drift coefficients on the characteristic relaxation time scale was analyzed. It was found that the resulting relaxation times exhibit a discrepancy relative to the kinetic coefficient estimates known from previous studies.

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arXiv2025

Relaxation of particle-hole type excitation in a Fermi system within the diffusion approximation of kinetic theory for the case of constant diffusion and drift coefficients

The time evolution of the distribution function for a particle-hole excitation in a Fermi system was calculated using the direct numerical solution of a nonlinear diffusion equation in momentum space. A phenomenological expression for calculating the relaxation time of such an excitation to its equilibrium value has been proposed. It is shown that the relaxation time is dependent on both the excitation energy and the mass number.

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