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Universe
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Kinetic Processes in Relativistic Domain
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Kinetic Processes in Relativistic Domain

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "High Energy Nuclear and Particle Physics".

Deadline for manuscript submissions: closed (1 May 2022) | Viewed by 11761

Special Issue Editor

Prof. Dr. Gregory Vereshchagin

E-Mail Website
Guest Editor
International Center for Relativistic Astrophysics Network (ICRANet), Piazza della Repubblica, 10, 65122 Pescara, PE, Italy
Interests: kinetic theory; plasma physics; astrophysics; cosmology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Relativistic kinetic theory provides the most fundamental level of description for physical systems that are composed of many particles. It accounts for microphysical properties and interactions of constituent particles and fields. This theory has widespread application in laboratory physics, as well as in astrophysics and cosmology. Notably, interest has grown in recent years as experimentalists have increasingly been making reliable measurements on physical systems, especially in relativistic domain. Such observed phenomena as the formation of dark matter halos and large-scale structure of the universe, origin of ultra-high energy cosmic rays, very high energy radiation and astrophysical neutrinos, relativistic shock waves in supernovae remnants and gamma-ray bursts can all be understood based on kinetic picture. On the theoretical side, significant progress has been made in the description of various nonequilibrium effects in relativistic plasmas, in the formulation of kinetic equations of self-gravitating systems, and in the description of particle acceleration in shocks.

The goal of this Special Issue is to cover the recent developments in kinetic theory, with particular attention to relativistic plasma, neutrino transport, self-gravitating systems and dark matter, radiative transfer in relativistic flows and other new and emergent topics in kinetic theory.

Prof. Dr. Gregory Vereshchagin
Guest Editor

Manuscript Submission Information

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Keywords

  • kinetic equations
  • radiative transfer
  • relativistic plasma
  • self-gravitating systems
  • electron-positron plasmas

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Published Papers (6 papers)

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Research

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53 pages, 690 KiB  
Article
The Secular Dressed Diffusion Equation
by Pierre-Henri Chavanis
Universe 2023, 9(2), 68; https://doi.org/10.3390/universe9020068 - 28 Jan 2023
Cited by 4 | Viewed by 1385
Abstract
The secular dressed diffusion equation describes the long-term evolution of collisionless systems of particles with long-range interactions, such as self-gravitating systems submitted to a weak external stochastic perturbation. We successively consider nonrotating spatially homogeneous systems, rotating spatially homogeneous systems, and spatially inhomogeneous systems. [...] Read more.
The secular dressed diffusion equation describes the long-term evolution of collisionless systems of particles with long-range interactions, such as self-gravitating systems submitted to a weak external stochastic perturbation. We successively consider nonrotating spatially homogeneous systems, rotating spatially homogeneous systems, and spatially inhomogeneous systems. We contrast the secular dressed diffusion equation applying to collisionless systems perturbed by an externally imposed stochastic field from the Lenard–Balescu equation applying to isolated systems evolving because of discreteness effects (“collisions”). We discuss the connection between these two equations when the external noise is produced by a random distribution of field particles. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
20 pages, 1823 KiB  
Article
Kinetics of Degenerate Electron–Positron Plasmas
by Gregory Vereshchagin and Mikalai Prakapenia
Universe 2022, 8(9), 473; https://doi.org/10.3390/universe8090473 - 9 Sep 2022
Cited by 3 | Viewed by 1819
Abstract
Relativistic plasma can be formed in strong electromagnetic or gravitational fields. Such conditions exist in compact astrophysical objects, such as white dwarfs and neutron stars, as well as in accretion discs around neutron stars and black holes. Relativistic plasma may also be produced [...] Read more.
Relativistic plasma can be formed in strong electromagnetic or gravitational fields. Such conditions exist in compact astrophysical objects, such as white dwarfs and neutron stars, as well as in accretion discs around neutron stars and black holes. Relativistic plasma may also be produced in the laboratory during interactions of ultra-intense lasers with solid targets or laser beams between themselves. The process of thermalization in relativistic plasma can be affected by quantum degeneracy, as reaction rates are either suppressed by Pauli blocking or intensified by Bose enhancement. In addition, specific quantum phenomena, such as Bose–Einstein condensation, may occur in such a plasma. In this review, the process of plasma thermalization is discussed and illustrated with several examples. The conditions for quantum condensation of photons are formulated. Similarly, the conditions for thermalization delay due to the quantum degeneracy of fermions are analyzed. Finally, the process of formation of such relativistic plasma originating from an overcritical electric field is discussed. All these results are relevant for relativistic astrophysics as well as for laboratory experiments with ultra-intense lasers. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
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15 pages, 433 KiB  
Article
A Multidimensional Multicomponent Gas Dynamic with the Neutrino Transfer in Gravitational Collapse
by Alexey G. Aksenov
Universe 2022, 8(7), 372; https://doi.org/10.3390/universe8070372 - 7 Jul 2022
Cited by 2 | Viewed by 1381
Abstract
The self-consistent problem of gravitational collapse is solved using 2D gas dynamics with taking into account the neutrino transfer in the flux-limited diffusion approximation. Neutrino are described by spectral energy density, and weak interaction includes a simplified physical model of neutrino interactions with [...] Read more.
The self-consistent problem of gravitational collapse is solved using 2D gas dynamics with taking into account the neutrino transfer in the flux-limited diffusion approximation. Neutrino are described by spectral energy density, and weak interaction includes a simplified physical model of neutrino interactions with nucleons. I investigate convection on the stage of the collapse and then in the center of the core, where the unstable entropy profile was probably formed. It is shown that convection has large scale. Convection appears only in the semitransparent region near the neutrinosphere due to non-equilibrium nonreversible neutronization. Convection increases the energy of emitted neutrino up to 15÷18 MeV. The obtained neutrino spectrum is important for the registration of low-energy neutrinos from a supernova. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
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10 pages, 272 KiB  
Article
Field-Theoretical Representation of Interactions between Particles: Classical Relativistic Probability-Free Kinetic Theory
by Anatoly Yu. Zakharov and Victor V. Zubkov
Universe 2022, 8(5), 281; https://doi.org/10.3390/universe8050281 - 12 May 2022
Cited by 2 | Viewed by 2163
Abstract
It was proven that the class of stable interatomic potentials can be represented exactly as a superposition of Yukawa potentials. In this paper, an auxiliary scalar field was introduced to describe the dynamics of a system of neutral particles (atoms) in the framework [...] Read more.
It was proven that the class of stable interatomic potentials can be represented exactly as a superposition of Yukawa potentials. In this paper, an auxiliary scalar field was introduced to describe the dynamics of a system of neutral particles (atoms) in the framework of classical field theory. In the case of atoms at rest, this field is equivalent to the interatomic potential, but in the dynamic case, it describes the dynamics of a system of atoms interacting through a relativistic classical field. A relativistic Lagrangian is proposed for a system consisting of atoms and an auxiliary scalar field. A complete system of equations for the relativistic dynamics of a system consisting of atoms and an auxiliary field was obtained. A closed kinetic equation was derived for the probability-free microscopic distribution function of atoms. It was shown that the finite mass of the auxiliary field leads to a significant increase in the effect of interaction retardation in the dynamics of a system of interacting particles. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
10 pages, 342 KiB  
Article
Post-Newtonian Jeans Equation for Stationary and Spherically Symmetrical Self-Gravitating Systems
by Gilberto Medeiros Kremer
Universe 2022, 8(3), 179; https://doi.org/10.3390/universe8030179 - 13 Mar 2022
Cited by 2 | Viewed by 1960
Abstract
The post-Newtonian Jeans equation for stationary self-gravitating systems is derived from the post-Newtonian Boltzmann equation in spherical coordinates. The Jeans equation is coupled with the three Poisson equations from the post-Newtonian theory. The Poisson equations are functions of the energy-momentum tensor components which [...] Read more.
The post-Newtonian Jeans equation for stationary self-gravitating systems is derived from the post-Newtonian Boltzmann equation in spherical coordinates. The Jeans equation is coupled with the three Poisson equations from the post-Newtonian theory. The Poisson equations are functions of the energy-momentum tensor components which are determined from the post-Newtonian Maxwell–Jüttner distribution function. As an application, the effect of a central massive black hole on the velocity dispersion profile of the host galaxy is investigated and the influence of the post-Newtonian corrections are determined. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
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Review

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17 pages, 770 KiB  
Review
The Principle of Maximum Entropy and the Distribution of Mass in Galaxies
by Jorge Sánchez Almeida
Universe 2022, 8(4), 214; https://doi.org/10.3390/universe8040214 - 28 Mar 2022
Cited by 10 | Viewed by 1957
Abstract
We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency [...] Read more.
We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time, and the fact that the mass distribution maximizing the classical Boltzmann–Gibbs entropy is unphysical. These arguments are questionable. In particular, when the Tsallis entropy that describes self-gravitating systems is used to define TE, the mass distributions that result (i.e., the polytropes) are physically sensible. This work spells out this and other arguments for TE and presents the polytropes and their properties. It puts forward empirical evidence for the mass distribution observed in galaxies to be consistent with polytropes. It compares polytropes with Sérsic functions and it shows how the DM halos resulting from cosmological numerical simulations become polytropes when efficient collisions are allowed. It also discusses pathways to thermalization bypassing two-body collisions. It finally outlines future developments including deciphering whether or not DM particles collide efficiently. Full article
(This article belongs to the Special Issue Kinetic Processes in Relativistic Domain)
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