arXiv subjects

A. V. Kuznetsov

Publications and source records attributed to A. V. Kuznetsov.

At least 19 recordsLinked to original sources

arXiv2025

Two-gap superconductor ZrB$_{12}$ with dynamic stripes and charge density waves: Crystal structure, physical properties and pairing mechanism

A review of long-term studies of ZrB$_{12}$ and LuB$_{12}$ superconductors with very similar conduction bands and phonon spectra, but with radically different (by a factor of 15-20) critical temperatures and magnetic fields is presented. A detailed analysis of well-known studies in combination with new results of structural, thermodynamic and charge transport measurements obtained here for these metallic dodecaborides with Jahn-Teller instability of the rigid boron network and with dynamic charge stripes allows us to conclude in favor of the primary role of nanoscale effects of electron phase separation, leading to the formation of one-dimensional dynamic chains with different configurations of fluctuating charges, which in the case of ZrB$_{12}$ are predominantly $2p$-states, and for LuB$_{12}$-$5d$-$2p$ states. We propose a new plasmon-phonon pairing mechanism in ZrB$_{12}$, which may be common to different classes of high-$T_c$ superconductors.

cond-mat.supr-con↗

arXiv2022

Position-space representation of charged particles' propagators in a constant magnetic field as an expansion over Landau levels

We have obtained propagators in the position space as an expansion over Landau levels for the charged scalar particle, fermion, and massive vector boson in a constant external magnetic field. The summation terms in the resulting expressions consisted of two factors, one being rotationally invariant in the 2-dimensional Euclidean space perpendicular to the direction of the field, and the other being Lorentz-invariant in the 1+1-dimensional space-time. The obtained representations are unique in the sense that they allow for the simultaneous study of the propagator from both space-time and energetic perspectives which are implicitly connected. These results contribute to the development of position-space techniques in QFT and are expected to be of use in the calculations of loop diagrams.

hep-th↗

arXiv2021

Symmetry-Breaking of Turbulent Flow in Porous Media Composed of Periodically Arranged Solid Obstacles

Microscale turbulence in porous media is a new physical phenomenon that exhibits unique properties unlike those in classical turbulence flows. At low values of porosity, the surface forces on the solid obstacles compete with the inertial force of the fluid flow to result in the formation of flow instabilities. In this paper, we report the origin and mechanism of a symmetry-breaking phenomenon in periodic porous media that causes a deviation in the direction of the mean flow from that of the applied pressure gradient. Large Eddy Simulation (LES) is used to simulate turbulent flow in a homogeneous porous medium consisting of a periodic, square lattice arrangement of cylindrical solid obstacles. Direct Numerical Simulation (DNS) is used to simulate the transient stages during symmetry breakdown and also to validate the LES method. Quantitative and qualitative observations are made from the following approaches: (1) macroscale momentum budget, (2) 2D & 3D flow visualization. The phenomenon draws its roots from the amplification of a flow instability that emerges from the vortex shedding process. The symmetry-breaking phenomenon is a pitchfork bifurcation that can exhibit multiple modes depending on the local vortex shedding process. The phenomenon is observed to be sensitive to the porosity, solid obstacle shape, and the Reynolds number. It is a source of macroscale turbulence anisotropy in porous media for symmetric solid obstacle geometries. The resulting macroscale flow field is oriented such that it does not align with the plane of symmetry of the porous matrix geometry. The principal axis of the Reynolds stress tensor is not aligned with any of the geometric axes of symmetry, nor with the direction of flow. Thus, symmetry-breaking in porous media involves new flow physics that should be taken into consideration while modeling flow inhomogeneity in the macroscale.

physics.flu-dyn↗

arXiv2020

How old are dense core vesicles residing in en passant boutons: Simulation of the mean age of dense core vesicles in axonal arbors accounting for resident and transiting vesicle populations

In neurons, neuropeptides are synthesized in the soma and are then transported along the axon in dense core vesicles (DCVs). DCVs are captured in varicosities located along the axon terminal called en passant boutons, which are active terminal sites that accumulate and release neurotransmitters. Recently developed experimental techniques allow for the estimation of the age of DCVs in various locations in the axon terminal. Accurate simulation of the mean age of DCVs in boutons requires the development of a model that would account for resident, transiting-anterograde, and transiting-retrograde DCV populations. In this paper, such a model is developed. The model is applied to simulating DCV transport in Drosophila type II motoneurons. The model simulates DCV transport and capture in the axon terminals and makes it possible to predict the age density distribution of DCVs in en passant boutons as well as DCV's mean age in boutons. The predicted prevalence of older organelles in distal boutons may explain the "dying back" pattern of axonal degeneration observed in dopaminergic neurons in Parkinson's disease. The predicted difference of two hours between the age of older DCVs residing in distal boutons and the age of younger DCVs residing in proximal boutons is consistent with an approximate estimate of age difference deduced from experimental observations. The age density of resident DCVs is found to be bimodal, which is because DCVs are captured from two transiting states: the anterograde transiting state that contains younger DCVs and the retrograde transiting state that contains older DCVs.

q-bio.SC↗

arXiv2020

Coordinate-space representation of a charged scalar particle propagator in a constant magnetic field expanded as a sum over the Landau levels

A coordinate-space representation for a charged scalar particle propagator in a constant magnetic field was obtained as a series over the Landau levels. Using the recently developed modified Fock-Schwinger method, an intermediate expression was constructed and symmetrized, thus, allowing for factorization of the series terms into two factors. The first one, a sum of Bessel functions, depends on time and $z$-coordinate, where the $z$-axis is chosen to be a direction of the magnetic field, and has a structure similar to the propagator of a free field. The second one, a product of a Laguerre polynomial and a damping exponential, depends on $x,y$-coordinates, which form a plane perpendicular to the direction of the magnetic field, and ensures the localized propagation in the $x,y$-plane.

hep-th↗

arXiv2020

Charged massive vector boson propagator in a constant magnetic field in arbitrary $ξ$-gauge obtained using the modified Fock-Schwinger method

We applied a recently published modified Fock-Schwinger (MFS) method to find the exact solution of the propagator equation for a charged vector boson in the presence of a constant magnetic field directly in the momentum space as a sum over Landau levels in arbitrary $ξ$-gauge. In contrast to the standard approaches for finding propagators, MFS method demonstrated several improvements in terms of computational complexity reduction and revealed simple internal structures in intermediate and final expressions, thus allowing to obtain new useful representations of the propagator.

hep-th↗

arXiv2016

Two components of critical current in YBa$_2$Cu$_3$O$_{7-δ}$ films

Combined action of weak and strong pinning centers on the vortex lattice complicates magnetic behavior of a superconductor since temperature and magnetic field differently affect weak and strong pinning. In this paper we show that contributions of weak and strong pinning into magnetization of the layered superconductor YBa$_2$Cu$_3$O$_{7-δ}$ can be separated and analyzed individually. We performed a careful analysis of temperature behavior of the relaxed superconducting current $J$ in YBa$_2$Cu$_3$O$_{7-δ}$ films which revealed two components of the current $J = J_1 +J_2$. A simple method of separation of the components and their temperature dependence in low magnetic fields are discussed. We found that $J_1$ is produced by weak collective pinning on the oxygen vacancies in CuO$_2$ planes while $J_2$ is caused by strong pinning on the Y$_2$O$_3$ precipitates. $J_1$ component weakly changes with field and quasi-exponentially decays with temperature, disappearing at $T \simeq 30$--40~K. Rapid relaxation of $J_1$ causes formation of the normalized relaxation rate peak at $T \simeq 20$~K. $J_2$ component is suppressed by field as $J_2\propto B^{-0.54}$ and decays with temperature following to the power law $J_2\propto(1 - T/T_\mathrm{dp} )^α$ where $T_\mathrm{dp}$ is the depinning temperature. Detailed comparison of the experimental data with pinning theories is presented.

cond-mat.supr-con↗

arXiv2015

Neutrino processes $ν\barν\to e^- e^+$ and $ν\to νe^- e^+$ in a strong magnetic field

The processes of neutrino production of electron-positron pairs, $ν\barν\to e^- e^+$ and $ν\to νe^- e^+$, in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, are analysed. The results can be applied for calculating the efficiency of the electron-positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disc considered by experts as the most possible source of a short cosmological gamma burst.

hep-ph↗

arXiv2015

Propagators of charged particles in an external magnetic field, expanded over Landau levels

Various forms of expressions for the propagators of charged particles in a constant magnetic field that should be used for investigations of electroweak processes in external uniform magnetic field are discussed. Formulas for the propagators of the Standard Model charged $W$- and scalar $Φ$-bosons in an arbitrary $ξ$-gauge, expanded over Landau levels, are derived for the first time.

hep-ph↗

arXiv2015

Generalized two-point tree-level amplitude $jf \to j^{\, \prime} f^{\, \prime}$ in a magnetized medium

The tree-level two-point amplitudes for the transitions $jf \to j^{\, \prime} f^{\, \prime}$, where $f$ is a fermion and $j$ is a generalized current, in a constant uniform magnetic field of an arbitrary strength and in charged fermion plasma, for the $jff$ interaction vertices of the scalar, pseudoscalar, vector and axial-vector types have been calculated. The generalized current $j$ could mean the field operator of a boson, or a current consisting of fermions, e.g. the neutrino current. The particular cases of a very strong magnetic field, and of the coherent scattering off the real fermions without change of their states (the "forward" scattering) have been analysed. The contribution of the neutrino photoproduction process, $γe\to e ν\bar ν$, to the neutrino emissivity has been calculated with taking account of a possible resonance on the virtual electron.

hep-ph↗

arXiv2014

Neutrino photoproduction on electron in dense magnetized medium

The effect of a strongly magnetized cold plasma on the Compton-like photoproduction of a neutrino-antineutrino pair on an electron, $γe \to e ν\bar ν$, has been considered. The contribution of this process to the neutrino emissivity in both the non-resonance and the resonance cases has been calculated with taking account of the photon dispersion properties in medium. Our results show that the neutrino emissivity owing to the $γe \to e ν\bar ν$ reaction is significantly modified as compared to the previously reported data.

hep-ph↗

arXiv2014

Generalized two-point tree-level amplitude $jf \to j^{\, \prime} f^{\, \prime}$ in a magnetized medium (extended version)

hep-ph↗

arXiv2014

Neutrino production of electron-positron pairs at excited Landau levels in a strong magnetic field

The process of neutrino production of electron positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analysed. The mean value of the neutrino energy loss due to the process $ν\to νe^- e^+$ is calculated. The result can be applied for calculating the efficiency of the electron-positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disc considered by experts as the most possible source of a short cosmological gamma burst. The presented research can be also useful for further development of the calculation technic for an analysis of quantum processes in external active medium, and in part in the conditions of moderately strong magnetic field, when taking account of the ground Landau level appears to be insufficient.

hep-ph↗

arXiv2014

Creation of electron-positron pairs at excited Landau levels by neutrino in a strong magnetic field

hep-ph↗

arXiv2012

The third type of fermion mixing and indirect limits on the Pati-Salam leptoquark mass

The low-energy manifestations of a minimal extension of the electroweak standard model based on the quark-lepton symmetry $SU(4)_V \otimes SU(2)_L \otimes G_R$ of the Pati-Salam type are analyzed. Given this symmetry the third type of mixing in the interactions of the $SU(4)_V$ leptoquarks with quarks and leptons is shown to be required. An additional arbitrariness of the mixing parameters could allow, in principle, to decrease noticeably the indirect lower bound on the vector leptoquark mass originated from the low-energy rare processes, strongly suppressed in the standard model.

hep-ph↗

arXiv2012

Tight binding approximation and magnetic susceptibility

The density of states and chemical potential as functions of temperature and filling degree of energy band were calculated. It was shown the peculiarity of concentration and temperature behavior of chemical potential is stipulated by Fermi statistics in the system with bounded energy spectrum. The magnetic initial susceptibility temperature trend was calculated for the half filled energy band. The sharp susceptibility maximum was obtained at low temperature and the susceptibility approaching to null value at absolute zero temperature was shown. Such behavior is discussed in the connection with the experimental results for lithium and potassium metals.

cond-mat.mtrl-sci↗

arXiv2012

The third type of fermion mixing in the lepton and quark interactions with leptoquarks

The low-energy manifestations of a minimal extension of the electroweak standard model based on the quark-lepton symmetry $SU(4)_V \otimes SU(2)_L \otimes G_R$ of the Pati--Salam type are analyzed. Given this symmetry the third type of mixing in the interactions of the $SU(4)_V$ leptoquarks with quarks and leptons is shown to be required. An additional arbitrariness of the mixing parameters could allow, in principle, to decrease noticeably the lower bound on the vector leptoquark mass originated from the low-energy rare processes, strongly suppressed in the standard model.

hep-ph↗

arXiv2011

Ultra-high energy neutrino dispersion in plasma and radiative transition $ν_L \to ν_R + γ$

Qualitative analysis of additional energy of neutrino and antineutrino in plasma is performed. A general expression for the neutrino self-energy operator is obtained in the case of ultra-high energies when the local limit of the weak interaction is not valid. The neutrino and antineutrino additional energy in plasma is calculated using the dependence of the $W$ and $Z$--boson propagators on the momentum transferred. The kinematical region for the neutrino radiative transition (the so-called "neutrino spin light") is established for some important astrophysical cases. For high energy neutrino and antineutrino, dominating transition channels in plasma, $ν_e + e^+ \to W^+$, $\barν_e + e^- \to W^-$ and $\barν_{\ell} + ν_{\ell} \to Z$, are indicated.

hep-ph↗