Showing papers in "Journal of Experimental and Theoretical Physics in 2020"

Review of Nontopological Solitons in Theories with U(1)-Symmetry

Abstract: We provide a review of nontopological solitonic solutions arising in theories with a complex scalar field and global or gauge U(1)-symmetry. It covers Q-balls, homogeneous charged scalar condensates, and nonlinear localized holes and bulges in a classically stable condensate. A historical overview is followed by the discussion of properties of solutions, including their stability, from different perspectives. Solitons in models with additional massive degrees of freedom are also revisited, and their relation to one-field Q-balls is showed. We also discuss theories with a gauge field giving rise to gauged Q-balls and theories with dynamical gravity giving rise to boson stars.

Direct Acceleration of a Charge in Vacuum by Linearly Polarized Radiation Pulses

Abstract: Analytic expression have been derived for the energy and momentum of a charged particle accelerated in vacuum by radiation pulses with linear polarization (plane-wave approximation). It is shown that these quantities are completely determined by the electrical area of pulses, viz., the integral of the electric field strength with respect to time.

Diffusion Properties of Oxygen in the γ-TiAl Alloy

Abstract: The oxygen absorption and migration energies in the γ-TiAl alloy are calculated using the projector augmented-wave method within the density functional theory. The phonon frequencies required for estimating the average jump rate are determined at initial and saddle oxygen positions. The temperature-dependent diffusion coefficient, the activation energy, and preexponential factor D0 are calculated along axes a and c using two models, which differ in oxygen interstitial positions, and two methods (statistical, Landman). The factors that determine the temperature-dependent diffusion coefficient in the Landman model are found. On the whole, the diffusion coefficients calculated within both methods are shown to agree satisfactorily; however, the Landman model can overestimate the contributions of low-barrier paths.

Transport Properties of Magnetic Nanogranular Composites with Dispersed Ions in an Insulating Matrix

Abstract: This review is devoted to an analysis of the electrical resistance, the magnetoresistance, and the anomalous Hall effect in magnetic “ferromagnetic metal–insulator” nanocomposites at a metal content near the percolation threshold and the memristive properties of the capacitor structures based on these nanocomposites. A high content (up to 1022 cm–3) of dispersed atoms in intergranular gaps leads to a logarithmic temperature dependence of the electrical resistance, a positive contribution to the magnetoresistance, the appearance of tunneling anomalous Hall effect, and a multifilament mechanism of resistive switching (which causes an adaptive character of memristor nanocomposites with dispersed atoms).

Effect of Light Element Impurities on the Edge Dislocation Glide in Nickel and Silver: Molecular Dynamics Simulation

Abstract: The influence of light element (C, N, O) impurities on the edge dislocation glide in fcc metals (Ni, Ag) is studied by molecular dynamics simulation. The introduction of impurity atoms is found to increase the dislocation glide threshold stress significantly, from 10 MPa in the pure metals at a temperature of 300 K to 1000–2000 MPa after the introduction of 10 at % impurity atoms. The increase in the threshold stress with the concentration of impurity atoms is shown to be caused by the Suzuki mechanism, i.e., the pinning of impurity atoms by the stacking fault between partial dislocations. The energies of binding of impurity atoms to stacking faults were determined for the metals under study. When temperature increases, the dislocation glide velocity in the pure metals decreases. After the introduction of impurity atoms, this dependence is reversed: the dislocation velocity increases gradually with temperature.

Test of Hybrid Metric-Palatini f(R)-Gravity in Binary Pulsars

Abstract: We developed the parameterized post-Keplerian formalism for hybrid metric-Palatini f(R)-gravity. We obtained analytical expressions in the general eccentric case for four post-Keplerian parameters: $$\dot {\omega }$$ , $${{\dot {P}}_{{\text{b}}}}$$ , r, and s. Using observational data of PSR J0737-3039 and PSR J1903+0327 we imposed restrictions on the parameters of hybrid f(R)-gravity and showed that this theory is not ruled out by the observations in strong field regime. In addition we obtained predictions for masses of systems components and found that considered astrophysical objects will be heavier than in GR.

Shadows from Spinning Black Holes in Extended Gravity

Abstract: When the shadow image of a supermassive black hole in the center of M87 was obtained a new era in the observational astrophysics began. The resolution improvement would allow to test extended gravity models at event horizon scales. We develop the method allowing to take into account the black hole rotation in black hole shadow modeling. It is demonstrated that the shadow of a black hole with a diameter smaller than 4RSw (RSw = 2M) cannot be represented in the terms of pure Kerr–Newman metric. Therefore, the detection of a shadow of such size would indicate that further expansions must be taken into account. This fact could give new indications on the detailed form of the theory of gravity at the considered scales.

Radiation from Elliptical Undulators with Magnetic Field Harmonics

Abstract: We analyze undulator radiation in some multiperiodic magnetic fields. We consider undulators with planar, helical, and elliptical axisymmetric magnetic fields with higher field harmonics. For these undulators, we obtain exact analytic expressions for generalized Bessel functions and Bessel coefficients. Analytic results are compared with the results of numerical simulation. We analyze the effect of additional third field harmonic on radiation emitted by these undulators. For a helical undulator with an additional asymmetric third harmonic field, it is found that the fifth harmonic of undulator radiation prevails over the third harmonic. We perform 3D simulation of radiation from free-electron laser with such an undulator using the specially developed numerical program that accounts for the electron energy spread in the beam as well as betatron oscillations. We analyze two-frequency undulator with a harmonic elliptically polarized magnetic field and simulate radiation of a free-electron laser with such an undulator.

The Effect of the Interaction of Excitations with the Interface between Nonlinear Media with a Switching on the Formation of Localized States

Abstract: Models of contacting media with stepwise nonlinearity are considered in the presence of interaction of excitations with the interface as a planar defect. In such media, an instantaneous switching from one level to another occurs when the field amplitude reaches a certain threshold value. New types of localized states with specific structure and properties are found. The structure of such states is determined by the formation of domains in the near-boundary regions, in which the values of certain parameters of the media differ from those in other regions. It is shown that, in the presence of interaction of excitations with the interface, new phenomena may occur that are related to the structural features of the field of localized states. The conditions for the existence of localized states are changed. The field can be maximized not only in the near-boundary region but also at the interface between a medium with stepwise nonlinearity and a linear medium. In the medium with stepwise nonlinearity containing a planar defect, the interaction of excitations with this defect leads to a decrease in the amplitude in the plane of the defect. As the intensity of interaction with the defect increases at a fixed localization energy, the domain width increases. It is shown that the threshold value of the total energy flow starting from which localized states exist and a domain is formed can be controlled by the intensity of the interaction of excitations with the interface.

Spin Dynamics for Antiferromagnets and Ultrafast Spintronics

Abstract: A brief review is given of the physical properties of antiferromagnets (AFMs) that can be used as active elements of terahertz and subterahertz range nanooscillators based on the excitation of spin oscillations by spin transfer torque. Possible schemes of such devices are considered. The analysis is carried out from a unified point of view on the basis of the nonlinear sigma model for the antiferromagnetic vector with regard to the magnetic symmetry of real AFMs. Specific properties of AFMs, first of all, the possibility of faster (compared to ferromagnets) spin dynamics, as well as the manifestations of antiferromagnetic ordering in galvanomagnetic and optical effects, are described. The history of the development of AFM physics is briefly discussed, first of all, those aspects of it that may be important for the practical application of AFMs, in particular, in ultrafast spintronics.

Gaseous Metal and the Problem of Vapor–Liquid (Insulator–Metal) Transition in Metal Vapors

Abstract: We consider the main properties of a gaseous metal, viz., the state of metal vapor adjoining the vapor–fluid transition binodal. The gaseous metal is a mixture of electron jellium and ion cores. The jellium concentration is calculated, and the region in which jellium electrons dominate over thermally ionized electrons is determined. We consider the main peculiarities and properties of the gaseous metal for conductivity as an example: the region of existence of the gaseous metal near its binodal as well as peculiarities in the behavior of conductivity on supercritical isotherms (the existence of a minimum and asymptotics). The physical meaning of the “asymptotic form” of the conductivity for increasing density is indicated as the conductivity of vapor along the binodal of the vapor–liquid coexistence binodal.

Interaction of a Magnetic Vortex with Magnetic Anisotropy Nonuniformity

Abstract: The problem of propagation of a magnetic inhomogeneity in the form of a magnetic vortex near a defect simulated by a crystallite with uniaxial anisotropy has been solved theoretically. The defect (crystallite) is implanted into a homogeneous 2D ferromagnetic matrix. Apart from the anisotropy energy, the term responsible for the existence of a centrosymmetric potential is included into the total energy. For calculations, we have used the method of collective variables (Thiele equation). We have considered the variants of bidirectional and unidirectional anisotropy of the crystallite. Analysis of the equations of motion for different directions of the anisotropy axis of the implanted defect has revealed the variety in the behavior of the vortex core as a quasiparticle. The vortex core can be trapped by the defect with equilibrium position of the vortex at rest directly on the crystallite or during its motion at a certain distance from it. It is shown that for a small damping parameter and in the case when the defect anisotropy axis lies in the plane of the magnet, the vortex moves so as if its core experiences the action of the repulsive axially symmetric potential.

Self-Consistent Model of Extragalactic Neutrino Flux from Evolving Blazar Population

Abstract: We study constraints on the population of neutrino emitting blazars imposed by the absence of doublets in astrophysical muon neutrino signal and z $$ \simeq $$ 0.3 redshift of nearest identified neutrino-emitting blazar (an order of magnitude further away than the nearest γ-ray emitting blazar). We show that in spite of the absence of correlation of neutrino arrival directions with positions of gamma-ray emitting blazars, cumulative blazar flux could explain most of astrophysical neutrino flux measured in muon neutrino channel. This is possible if the population of neutrino emitting blazars has experienced rapid positive evolution at least as (1 + z)5 at z $$ \lesssim $$ 1. Such a model avoids previously derived constraint on the low level of blazar contribution to extragalactic neutrino flux because gamma-ray and neutrino fluxes are dominated by different sets of blazars. Rapid evolution of neutrino emitting blazars could be explained by the fact that only rapidly evolving sub-population of blazars, which can include parts of Flat Spectrum Radio Quasar and bright BL Lac populations, are efficient neutrino sources, although their neutrino luminosity has to be systematically lower than the γ-ray luminosity.

Composite Topological Objects in Topological Superfluids

Abstract: The spontaneous phase coherent precession of magnetization, discovered in 1984 by Borovik-Romanov, Bunkov, Dmitriev, and Mukharskiy [1] in collaboration with Fomin [2], became now an important experimental tool for study complicated topological objects in superfluid 3He.

Aluminum-Carbon Interaction at the Aluminum-Graphene and Aluminum-Graphite Interfaces

Abstract: The interaction of liquid and solid aluminum with the graphene and graphite surfaces is studied using the density functional theory and a molecular dynamics simulation. The Morse potential is parameterized using the results of ab initio calculations in order to describe the interaction between aluminum and carbon atoms. This potential is used to investigate the interaction of a molten aluminum drop with the (0001) graphite surface theoretically. The properties of the free aluminum melt surface and the contact surface formed upon wetting graphite by the molten drop are calculated. The calculation results agree well with the available experimental data.

Trojan Horse Attacks, Decoy State Method, and Side Channels of Information Leakage in Quantum Cryptography

Abstract: Early proofs of key secrecy in quantum cryptography systems were based on the assumption that the transmitting and receiving stations are completely isolated from the outside world—the eavesdropper. However, this condition cannot be implemented in practice since quantum cryptography systems are open systems in the sense that the eavesdropper may have indirect access, for example, through a fiber communication channel, to the critical elements of the equipment (phase modulators, intensity modulators, etc.) using active probing of the state of these elements. The state of the elements carries information about the transmitted key. In addition, the eavesdropper can use passive detection of side radiation from the receiving and transmitting equipment. Signals in side channels of information leakage may have extremely low intensity and are actually quantum signals. The eavesdropper may use the joint measurement of quantum information states in the communication channel and of states in various side channels of information leakage. The paper considers both passive attacks with measurement of side radiation and active attacks involving the probing of the states of the phase modulator and the intensity modulator, as well as backscattering radiation of single-photon avalanche detectors, which occurs during detecting information states on the receiver side. Combined attacks are also considered. The decoy state method is generalized with regard to active probing attacks, and boundaries for state parameters in side communication channels are obtained that guarantee secret key distribution for a given length of the communication channel.

Microwave Giant Magnetoresistance and Ferromagnetic and Spin-Wave Resonances in (CoFe)/Cu Nanostructures

Abstract: The microwave phenomena that occur in magnetic multilayer (CoFe)/Cu nanostructures, which have a giant magnetoresistance, are studied. The transmission of waves through a nanostructure is used to investigate the microwave giant magnetoresistance effect. The changes in the transmission coefficient at frequencies of 29–38 GHz are found to exceed the relative magnetoresistance, which distinguishes the system under study from the nanostructures studied earlier. Ferromagnetic and spin-wave resonances are used to study the angular dependences of the microwave absorption spectra of a multilayer (CoFe/Cu)n nanostructure. The following parameters are determined: the critical angle that determines the boundaries of the ranges of excitation of uniform and nonuniform spin modes, the type of boundary conditions describing the pinning of spins on the outer nanostructure surfaces, and the surface anisotropy and exchange interaction constants.

Spatio-Temporal Analysis of Surface Waves Generating Octupole Vortices in a Square Domain

Abstract: In this study, we examine the underlying surface wave dynamics forming an octupole structure of vortices on the air–water interface. The surface waves are generated by a square wavemaker made of four cylindrical edges half-submerged on the interface. These waves direct the motion of floaters into gyrating trajectories, forming two counter-rotating vortices along each edge of the wavemaker and generating the overall octupole pattern. We 3D reconstruct the wave heights and describe the underlying flow through spatio-temporal analysis. Specifically, we decompose the overall wave field into components coming from the edges and corners of the wavemaker. To our knowledge, we are first to obtain a closed-form solution for a velocity potential, via a superposition of edge and phase-shifted oblique progressive waves produced by the wavemaker, to qualitatively model these octupole vortices. The methodology outlined provides a phenomenological approach to characterize the flow that may be useful for characterizing waves inside arbitrary finite-sized domains.

Attosecond Dynamics of Photoexcitation of the Hydrogen Atom by Ultrashort Laser Pulses

Abstract: The dynamics of photoexcitation of the hydrogen atom in the discrete and continuous spectra under the action of laser pulses in the attosecond range of time and pulse durations has been analyzed using perturbation theory. It is shown that over time interval shorter than or on the order of pulse duration, the time dependence of the photoexcitation probability is generally oscillating by nature. It has been established that for certain values of parameters, the envelope of this dependence has a peak, the position of which is determined by the pulse duration and carrier frequency.

Shear Modulus Relaxation and Thermal Effects in a Zr 65 Cu 15 Ni 10 Al 10 Metallic Glass after Inhomogeneous Plastic Deformation

Abstract: The shear modulus and enthalpy relaxation in a deformed Zr65Cu15Ni10Al10 metallic glass has been investigated. It has been established that inhomogeneous plastic deformation leads to a decrease in the unrelaxed shear modulus and a change in its relaxation kinetics upon subsequent heat treatment. An analysis of the calorimetric data shows that inhomogeneous plastic deformation leads to the accumulation of an additional internal energy in the metallic glass, which, however, causes no shear modulus relaxation.

Compression and Burning of a Thermonuclear Target upon Shock Ignition under the Conditions of Laser Beam Irradiation Symmetry Violation

Abstract: The influence of heating homogeneity violations in a laser thermonuclear target designed for shock ignition on the target compression and burning has been studied. We have performed our studies based on two-dimensional hydrodynamic simulations when modeling the target heating homogeneity violations due to various factors of symmetry violation of the target irradiation by a finite number of laser beams. The gains have been calculated at various perturbation amplitudes of the spatial distribution of absorbed energy in the target for two characteristic cases—low and high dominant perturbation modes. The first and second cases refer, respectively, to the factors of regular irradiation homogeneity violation due to a finite number of laser beams and a target offset from the focusing point and the factors of stochastic irradiation homogeneity violation related to laser beam energy imbalance, beam mispointing, and beam mistiming. We show that for a target designed for shock ignition the factors of regular irradiation homogeneity violation are much more dangerous than those for a spark ignition target.

Casimir and Surface Tension Forces on a Single Interacting Bose–Einstein Condensate in Canonical Ensemble

Abstract: The forces on a single Bose–Einstein condensate confined between two parallel plates consist of two components, namely, surface tension force and Casimir force. In canonical ensemble, these forces are quite different from the one in grand canonical ensemble. In small region with distance $$\ell $$ between two parallel plates, using double parabola approximation, we find that surface tension force decreases as $${{\ell }^{{ - 3}}}$$, whereas the Casimir force, in one-loop approximation of the quantum field, is proportional to $${{\ell }^{{ - 13/2}}}$$. The total force is also considered and its veer is found.

On the Existence of Hypersonic Electrostatic Solitons (Estimation of Limiting Mach Numbers of Ion-Sound Solitons in a Warm Plasma)

Abstract: We develop a nonlinear theory of ion-sound waves in a collisionless warm electron–ion plasma. The theory is based on analysis of the Sagdeev pseudopotential. We consider two (isothermal and adiabatic) models of ion-sound waves. We calculate the dependences of the maximal Mach number for solitons on reduced temperature (nonequilibrium parameter) of the plasma in both models. It is shown that the maximal value of the Mach number cannot exceed the fundamental limit (2.54). We have answered the question concerning the existence of hypersonic ion-sound solitons: hypersonic solitons do not exist.

Scattering and Absorption of Light by a Monolayer of Spherical Particles under Oblique Illumination

Abstract: The problem of light scattering and absorption by a monolayer of homogeneous spherical particles at an arbitrary angle of incidence of a plane wave, which determines the phase shift between the averaged fields in the particles, has been solved. The solution is based on the quasi-crystalline approximation of the theory of multiple scattering of waves, the mean-field approximation, and the multipole expansion of the fields and the tensor Green function in terms of vector spherical wave functions. Formulas for determining the angular distribution of the incoherently scattered field intensity, the incoherent scattering, absorption, coherent transmission, and reflection coefficients have been derived. The dependences of these characteristics on the direction of illumination are illustrated using partially ordered monolayers of dielectric and semiconductor particles as an example. It is shown that: (i) under oblique illumination the angular distribution of the scattered radiation in azimuthal scattering angle for any polarization of the incident wave (except for p and s) is asymmetric relative to the plane of incidence, (ii) the maximum of the angular distribution of the radiation transmitted through the monolayer can approach its normal with increasing angle of incidence and/or concentration of particles, (iii) there exist conditions under which the bulk of the scattered radiation is concentrated in the direction opposite to the direction of the incident radiation, and (iv) the dependence of the monolayer absorption coefficient on the illumination angle has extrema whose positions and magnitudes are determined by the polarization of the incident wave.

On Peculiarities in Localization of Light in Cholesteric Liquid Crystals

Abstract: We have analyzed peculiarities in the localization of light in a layer of a cholesteric liquid crystal (CLC) for the normal incidence of light. It is shown that dielectric boundaries strongly affect the localization. For the minimal influence of dielectric boundaries (i.e., for ns = $$\sqrt {{{\varepsilon }_{m}}} $$ ), the total field for the eigenmodes in the CLC layer varies smoothly upon a displacement along the z axis directed along the axis of the medium (here, em is the mean permittivity of the CLC layer and ns is the refractive index of the external medium). When ns differs from $$\sqrt {{{\varepsilon }_{m}}} $$ or when the polarization of incident light differing from the polarization of the eigenmodes, oscillations appear in the dependence of the energy of the total wave field in the CLC layer on z. It is shown that the amount of the energy stored in the CLC layer depends on ns, and the total accumulated energy in the CLC layer increases monotonically with ns.

Weak Antiferromagnet Iron Borate FeBO3. Classical Object for Magnetism and the State of the Art

Abstract: The simple lattice and magnetic structure, the high Neel temperature, the narrow antiferromagnetic resonance line of FeBO3, and the narrow electron paramagnetic resonance line of its isostructural diamagnetic analogs MBO3:Fe3+ (M = Ga, In, Sc, Lu) make iron borate unique for investigations and applications. Iron borate is a model crystal for numerous experimental and theoretical studies, including spin crossovers and metallization at megabar pressures and many-electron effects in optics and X-ray spectroscopy. The recent works dealing with the investigation of the properties of FeBO3 are reviewed.

Spectral Characteristics of Stochastic Motion in the System of Two Interacting Particles

Abstract: We report on the results of analytic and numerical investigations of spectral characteristics of the stochastic (thermal) motion of two charged particles in the anisotropic electric field of a trap. We propose analytic relations for the spectral density of displacements in such a system with homogeneous and inhomogeneous heat sources, including the spectral densities for each particle, as well as for their total and mutual displacements. The resulting relations have been verified by numerical simulation of the problem.

Temperature Dependence of the Order Parameter of the Polar Phase of Liquid 3He in a Nematic Aerogel

Abstract: It is proved that in the polar phase of superfluid 3He stabilized by a nematic aerogel the temperature dependence of the gap in the spectrum of Fermi excitations must be the same as that in the bulk polar phase without foreign impurities when the liquid quasiparticles are specularly reflected from the aerogel strands. The analogy with the Anderson theorem for conventional superconductors is discussed.

Search for Ultra-High-Energy Neutrinos with the Telescope Array Surface Detector

Abstract: We present an upper limit on the flux of ultra-high-energy down-going neutrinos for E > 1018 eV derived with the nine years of data collected by the Telescope Array surface detector (from November 5, 2008 to October 5, 2017). The method is based on the multivariate analysis technique, so-called Boosted Decision Trees (BDT). Proton-neutrino classifier is built upon 16 observables related to both the properties of the shower front and the lateral distribution function.

Superfluid 3 He in a Nematic Aerogel

Abstract: In nematic aerogels, their constituent fibers are oriented along the same direction. In liquid 3He filling such aerogels, the scattering of Fermi quasiparticles at ultralow temperatures becomes anisotropic. This makes it possible to obtain new superfluid phases of 3He, which are not observed in bulk 3He. In this article, results of NMR investigation of these new superfluid phases of 3He in aerogels with different porosities are compared. We describe the methods for identifying these phases and consider some topological defects observed in them.