arXiv subjects

Vl. V. Kocharovsky

Publications and source records attributed to Vl. V. Kocharovsky.

15 recordsLinked to original sources

arXiv2025

The skin effect in anomalous transport of charged particles in plasma with a microturbulent magnetic field. I. Isotropic plasma

The influence of electromagnetic skin effect on anomalous charged particle transport in dense, non-relativistic, collisionless plasma with a small-scale turbulent magnetic field was investigated using quasi-linear kinetic equations, through both analytical and numerical methods. Analytical expressions for the diffusion tensor components in the Fokker-Planck equation that take this effect into account have been found. The equation was solved numerically in the case of magnetostatic turbulence. It has been demonstrated that the skin effect increases the mean free path of particles in turbulent plasma, thereby reducing its anomalous resistance. It also leads to anisotropy in particle scattering, resulting in anisotropy in their stationary velocity distribution, which increases as the screening parameter grows. Approximate analytical formulas for the effective mobility of charged particles and the electric conductivity of plasma with isotropic magnetostatic turbulence have been obtained.

physics.plasm-ph↗

arXiv2025

Explosive growth of large-scale magnetic fluctuations due to particle scattering on developed small-scale Weibel turbulence in magnetoactive plasma

The analytical theory of non-linear generation of large-scale magnetic turbulence in anisotropic magnetoactive plasma in the quasilinear approximation without taking into account the direct non-linear interaction of individual harmonics is constructed. It is shown that anomalous collisions of particles due to scattering on small-scale fluctuations of the developed Weibel turbulence lead to instability of long-wave harmonics, which are stable in the linear approximation. The non-linear growth of such harmonics at a given anisotropy of the particle velocity distribution, consistent with the dynamics of short-wave perturbations at the saturation stage and possible anisotropic particle injection, occurs in the superexponential regime and corresponds to an explosive-type instability. The growth law of the large-scale magnetic field is found analytically and the critical time of explosive instability is estimated.

physics.plasm-ph↗

arXiv2025

Quasilinear interaction between Langmuir and Weibel turbulence in a beam-plasma system

To analyze the joint development of two-stream and filamentation kinetic instabilities in a plasma with a particle beam, a quasilinear approach has been developed that accounts for the integral nonlinear interaction of modes arising from the variation of the spatially averaged velocity distribution function of the particles. On this basis, a numerical study has been carried out within the initial two-dimensional problem for a range of characteristic parameters of the plasma and the beam, focusing on the evolution of Langmuir (two-stream) and Weibel (filamentation) turbulence spectra. It has been established that the evolving Weibel-type magnetic turbulence can significantly reshape the region of the velocity distribution that is resonant with Langmuir waves, thereby strongly influencing the formation and particularly the damping of Langmuir turbulence. In turn, the Langmuir-type quasi-electrostatic turbulence can lead to substantial isotropization of the particle velocity distribution, thus altering the growth rates, evolution, and saturation levels of the Weibel turbulence modes.

physics.plasm-ph↗

arXiv2025

Alfvén pulse at chromospheric footpoints of magnetic loops and generation of the super-Dreicer electric field

A self-similar solution of the linearised magnetohydrodynamic equations describing the propagation of the Alfvén pulse in an axially symmetric magnetic tube of variable diameter is obtained. The electric field component induced by the non-linear Alfvén wave and directed along the tube surface, i.e., accelerating particles along the magnetic field, is determined on the basis of the perturbation theory and specified to the case of a magnetic flux tube homogeneous over its cross section. For the chromospheric tubes, whose configuration is given by the barometric law of plasma pressure decrease, the conditions for achieving the super-Dreicer electric field limit necessary to drive the accelerated high-energy electrons into the coronal part of the loop are established.

physics.plasm-ph↗

arXiv2023

Towards the simplest model of quantum supremacy: Atomic boson sampling in a box trap

We describe boson sampling of interacting atoms from the noncondensed fraction of Bose-Einstein-condensed (BEC) gas confined in a box trap as a new platform for studying computational #P-hardness and quantum supremacy of many-body systems. We calculate the characteristic function and statistics of atom numbers via newly found hafnian master theorem. Using Bloch-Messiah reduction, we find that interatomic interactions give rise to two equally important entities - eigen-squeeze modes and eigen-energy quasiparticles - whose interplay with sampling atom states determines behavior of the BEC gas. We infer that two necessary ingredients of #P-hardness, squeezing and interference, are self-generated in the gas and, contrary to Gaussian boson sampling in linear interferometers, external sources of squeezed bosons are not required.

cond-mat.quant-gas↗

arXiv2009

Time-Integrated Evidence for Superfluorescence from Dense Electron-Hole Magneto-Plasmas in Semiconductor Quantum Wells

Cooperative spontaneous recombination (superfluorescence) of electron-hole plasmas in semiconductors has been a challenge to observe due to ultrafast decoherence. We argue that superfluorescence can be achieved in quantum-confined semiconductor systems and present experimental evidence for superfluorescence from high-density photoexcited electron-hole plasmas in quantum wells under high magnetic fields (> 20 T). At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. Changes in the linewidth, carrier density, and magnetic field scaling of the emission spectra correlate precisely with the onset of random directionality and are consistent with cooperative recombination. We further investigate the effects of spot size, temperature, and excitation geometry on the emission properties.

cond-mat.mes-hall↗

arXiv2006

Off-axis emission from relativistic plasma flows

We show that there is no universal law describing how the spectra and luminosity of synchrotron and inverse Compton radiation from relativistic jets change with increasing observation angle. Instead, the physics of particle acceleration leaves pronounced imprints in the observed spectra and allows for a freedom in numerous modifications of them. The impact of these effects is the largest for high-energy radiation and depends on the details of particle acceleration mechanism(s), what can be used to discriminate between different models. Generally, the beam patterns of relativistic jets in GeV-TeV spectral domain are much wider than the inverse Lorentz factor. The off-axis emission in this energy range appear to be brighter, have much harder spectra and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The implications include the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars, and the prediction of GeV-TeV afterglow from transient jet sources, such as Gamma-Ray Bursts. We also discuss the phenomenon of beam-pattern broadening in application to neutrino emission.

astro-ph↗

arXiv2006

Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma

We investigate photoluminescence from a high-density electron-hole plasma in semiconductor quantum wells created via intense femtosecond excitation in a strong perpendicular magnetic field, a fully-quantized and tunable system. At a critical magnetic field strength and excitation fluence, we observe a clear transition in the band-edge photoluminescence from omnidirectional output to a randomly directed but highly collimated beam. In addition, changes in the linewidth, carrier density, and magnetic field scaling of the PL spectral features correlate precisely with the onset of random directionality, indicative of cooperative recombination from a high density population of free carriers in a semiconductor environment.

cond-mat.other↗

arXiv2005

On dynamics of relativistic shock waves with losses in gamma-ray burst sources

Generalization of the self-similar solution for ultrarelativistic shock waves (Blandford & McKee, 1976) is obtained in presence of losses localized on the shock front or distributed in the downstream medium. It is shown that there are two qualitatively different regimes of shock deceleration, corresponding to small and large losses. We present the temperature, pressure and density distributions in the downstream fluid as well as Lorentz factor as a function of distance from the shock front.

astro-ph↗

arXiv2005

High-energy emission from off-axis relativistic jets

We analyze how the spectrum of synchrotron and inverse Compton radiation from a narrow relativistic jet changes with the observation angle. It is shown that diversity of acceleration mechanisms (in particular, taking the converter mechanism (Derishev et al. 2003) into account) allows for numerous modifications of the observed spectrum. In general, the off-axis emission in GeV-TeV energy range appears to be brighter, has a much harder spectrum and a much higher cut-off frequency compared to the values derived from Doppler boosting considerations alone. The magnitude of these effects depends on the details of particle acceleration mechanisms, what can be used to discriminate between different models. One of the implications is the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars. We also discuss the broadening of beam pattern in application to bright transient jet sources, such as Gamma-Ray Bursts.

astro-ph↗

arXiv2003

Particle Acceleration through Multiple Conversions from Charged into Neutral State and Back

We propose a new way of quick and very efficient acceleration of protons and/or electrons in relativistic bulk flows. The new mechanism takes advantage of conversion of particles from the charged state (protons or electrons/positrons) into neutral state (neutrons or photons) and back. In most cases, the conversion is photon-induced and requires presence of intense radiation fields, but the converter acceleration mechanism may also operate via inelastic nucleon-nucleon collisions. Like in the traditional model -- ``stochastic'' (or diffusive) acceleration, -- the acceleration cycle in our scenario consists of escape of particles from the relativistic flow followed by their return back after deflection from the ambient magnetic field. The difference is that the charge-changing reactions, which occur during the cycle, allow accelerated particles to increase their energies in each cycle by a factor roughly equal to the bulk Lorentz factor squared. The emerging spectra of accelerated particles can be very hard and their cut-off energy in some cases is larger than in the standard mechanism. This drastically reduces the required energy budget of the sources of the highest-energy particles observed in cosmic rays. Also, the proposed acceleration mechanism may serve as an efficient means of transferring the energy of bulk motion to gamma-radiation and, if the accelerated particles are nucleons, routinely produces high-energy neutrinos at $\sim 50 %$ relative efficiency.

astro-ph↗

arXiv2002

Constraints on the Extremely High-Energy Cosmic Ray Accelerators from Classical Electrodynamics

We find the general requirements, set by classical electrodynamics, to the sources of extremely high-energy cosmic rays (EHECRs). It is shown that the parameters of EHECR accelerators are strongly limited not only by the particle confinement in large-scale magnetic field or by the difference in electric potentials (generalized Hillas criterion), but also by the synchrotron radiation, the electro-bremsstrahlung, or the curvature radiation of accelerated particles. Optimization of these requirements in terms of accelerator's size and magnetic field strength results in the ultimate lower limit to the overall source energy, which scales as the fifth power of attainable particle energy. Hard gamma-rays accompanying generation of EHECRs can be used as a probe for potential acceleration sites. We apply the results to several populations of astrophysical objects -- potential EHECR sources -- and discuss their ability to accelerate protons to $10^{20}$ eV and beyond. A possibility to gain from ultrarelativistic bulk flows is emphasized, with Active Galactic Nuclei and Gamma-Ray Bursts being the examples.

astro-ph↗

arXiv2001

The influence of free neutrons on dynamics and radiation of astrophysical plasmas

We present arguments in favor of the presence of free neutrons in plasmas generated by compact astrophysical objects and find conditions necessary for the formation of the neutron component. The broad range of phenomena caused by neutrons includes both dynamical (sources' variability, transition of fireballs to the two-flow regime) and kinetic (fission of helium nuclei by neutrons, electromagnetic cascade, emission in annihilation and nuclear lines, neutrino losses) effects. The presented theory can be applied to internal regions of accretion disks, jets in microquasars, and gamma-ray burst (GRB) fireballs.

astro-ph↗

arXiv2001

Physical parameters and emission mechanism in Gamma-Ray Bursts

Detailed information on the physical parameters in the sources of cosmological Gamma-Ray Bursts (GRBs) is obtained from few plausible assumptions consistent with observations. Model-independent requirements posed by these assumptions on the emission mechanism in GRBs are formulated. It is found that the observed radiation in sub-MeV energy range is generated by the synchrotron emission mechanism, though about ten per cent of the total GRB energy should be converted via the inverse Compton process into ultra-hard spectral domain (above 100 GeV). We estimate the magnetic field strength in the emitting region, the Lorentz factor of accelerated electrons, and the typical energy of IC photons. We show that there is a "line-of-death" relation for GRBs and derive from this relation the lower limits on both GRB duration and GRB variability timescale. The upper limit on the Lorentz factor of GRB fireballs is also found. We demonstrate that steady-state electron distribution consistent with the Compton losses may produce different spectral indices, e.g., 3/4 as opposed to the figure 1/2 widely discussed in the literature. It is suggested that the changes in the decline rate observed in the lightcurves of several GRB afterglows may be due to the time evolution of spectral break, which appears in the synchrotron emission generated by steady-state self-consistent electron distribution.

astro-ph↗

arXiv2000

Infrared generation in low-dimensional semiconductor heterostructures via quantum coherence

A new scheme for infrared generation without population inversion between subbands in quantum-well and quantum-dot lasers is presented and documented by detailed calculations. The scheme is based on the simultaneous generation at three frequencies: optical lasing at the two interband transitions which take place simultaneously, in the same active region, and serve as the coherent drive for the IR field. This mechanism for frequency down-conversion does not rely upon any ad hoc assumptions of long-lived coherences in the semiconductor active medium. And it should work efficiently at room temperature with injection current pumping. For optimized waveguide and cavity parameters, the intrinsic efficiency of the down-conversion process can reach the limiting quantum value corresponding to one infrared photon per one optical photon. Due to the parametric nature of IR generation, the proposed inversionless scheme is especially promising for long-wavelength (far- infrared) operation.

quant-ph↗