arXiv subjects

V. R. Khalilov

Publications and source records attributed to V. R. Khalilov.

At least 19 recordsLinked to original sources

arXiv2020

On the creation of charged massless fermion pair by a photon in crossed electromagnetic field

Creation of charged massless fermion pair by a photon in external constant crossed electromagnetic field is considered. For this we use the expression of elastic scattering amplitude (EAS) of photon in the one-loop approximation of massive quantum electrodynamics obtained earlier and calculate its massless limit. We assume that the imaginary part of EAS of photon describes the total probability of charged massless fermion pair creation in external electromagnetic field. Photon emission by a charged massless fermion is also studied in constant crossed electromagnetic field. We obtain the total probability of photon emission calculating elastic scattering amplitude of charged massive fermion in the electromagnetic field in the massless limit.

hep-ph↗

arXiv2019

On elastic scattering amplitude of planar charged fermions in a constant magnetic field

The elastic scattering amplitude (ESA) is obtained in the one-loop approximation of the 2+1 dimensional quantum electrodynamics (QED$_{2+1}$) for planar charged fermions in an external constant magnetic field. We obtain the elastic scattering amplitude in the corresponding massive theory and then discuss and calculate the massless limit of ESA. The imaginary part of ESA are related to the total probability of photons emission by charged fermions in the considered magnetic field. Simple analytical formulas are obtained when planar charged fermions in initial states occupy high excited Landau levels.

hep-ph↗

arXiv2019

Effect of vacuum polarization of charged massive fermions in an Aharonov--Bohm field

The effect of vacuum polarization of charged massive fermions in an Aharonov-Bohm (AB) potential in 2+1 dimensions is investigated. The causal Green's function of the Dirac equation with the AB potential is represented via the regular and irregular solutions of the two-dimensional radial Dirac equation. It is shown that the vacuum current density contains the contribution from free filled states of the negative energy continuum as well as that from a bound unfilled state, which can emerge in the above background due to the interaction of the fermion spin magnetic moment with the AB magnetic field while the induced charge density contains only the contribution from the bound state. The expressions for the vacuum charge and induced current densities are obtained (recovered for massless fermions) for the graphene in the field of infinitesimally thin solenoid perpendicular to the plane of a sample. We also find the bound state energy as a function of magnetic flux, fermion spin and the radius of solenoid as well as discuss the role of the so-called self-adjoint extension parameter and determine it in terms of the physics of the problem.

quant-ph↗

arXiv2018

Radiative dynamical mass of planar charged fermion in a constant homogeneous magnetic field

The effective Lagrangian and mass operator are calculated for planar charged massive and massless fermions in a constant external homogeneous magnetic field in the one-loop approximation of the 2+1 dimensional quantum electrodynamics (QED$_{2+1}$). We obtain the renormalizable effective Lagrangian and the fermion mass operator for a charged fermion of mass $m$ and then calculate these quantities for the massless case. The radiative corrections to the mass of charged massless fermion when it occupies the lowest Landau level are found for the cases of the pure QED$_{2+1}$ as well as the so-called reduced QED$_{3+1}$ on a 2-brane. The fermion masses were found can be generated dynamically by an external magnetic field in the pure QED$_{2+1}$ if the charged fermion has small bare mass $m_0$ and in the reduced QED$_{3+1}$ on a 2-brane even at $m_0=0$. The dynamical mass seems to be likely to be revealed in monolayer graphene in the presence of constant homogeneous magnetic field (normal to the graphene sample).

hep-ph↗

arXiv2017

Quasi-stationary states and fermion pair creation from a vacuum in supercritical Coulomb field

Creation of charged fermion pair from a vacuum in the so-called supercritical Coulomb potential is examined for the case when created pair moves in one plane. In which case the quantum dynamics of charged massive or massless fermions can be described by the two-dimensional Dirac Hamiltonians with a Coulomb potential. These Hamiltonians are singular and require the additional definition in order for them to be treated as self-adjoint quantum-mechanical operators. We construct the self-adjoint two-dimensional Dirac Hamiltonians with a Coulomb potential and determine the quantum-mechanical states for such Hamiltonians in the corresponding Hilbert spaces of square-integrable functions. We determine the scattering amplitude in which the self-adjoint extension parameter is incorporated and then obtain the equations implicitly defining the possible discrete energy spectra of the self-adjoint Dirac Hamiltonians with a Coulomb potential. It is shown that the quantum system in the presence of a supercritical Coulomb potential becomes unstable which manifests in the appearance of quasi-stationary states in the lower (negative) energy continuum. The energy spectrum of these states is quasi-discrete, consists of broadened levels whose width is related to the inverse lifetime of the quasi-stationary state as well as the creation probability of charged fermion pair by supercritical Coulomb field. Explicit analytical expressions for the creation probabilities of charged (massive or massless) fermion pair are obtained in a supercritical Coulomb field.

hep-ph↗

arXiv2017

Quantum states of a neutral massive fermion with an anomalous magnetic moment in an external electric field

The planar non-relativistic quantum dynamics of a neutral massive fermion with an anomalous magnetic moment (AMM) in the presence of the electric field of infinitely long and thin thread with a charge density distributed uniformly along it (an Aharonov--Casher field) is examined. The relevant Hamiltonian is singular and requires additional specification of a one-parameter self-adjoint extension, which can be given in terms of physically acceptable (self-adjoint) boundary conditions. We find all possible self-adjoint Hamiltonians with an Aharonov--Casher field (ACF) by constructing the corresponding Hilbert space of square-integrable functions, including the $r = 0$ region, for all their Hamiltoniahs. We determine the most relevant physical quantities, such as energy spectrum and wave functions and discuss their correspondence with those obtained by the physical regularization procedure. We show that energy levels of bound states are simple poles of the scattering amplitude. Expressions for the scattering amplitude and cross section depending on the fermion spin are reexamined.

quant-ph↗

arXiv2016

Plane density of induced vacuum charge in a supercritical Coulomb potential

An expression for the density of a planar induced vacuum charge is obtained in a strong Coulomb potential in coordinate space. Treatment is based on a self-adjoint extension approach for constructing of the Green's function of a charged fermion in this potential. Induced vacuum charge density is calculated and analyzed at the subcritical and supercritical Coulomb potentials for massless and massive fermions. The behavior of the obtained vacuum charge density is investigated at long and short distances from the Coulomb center. The induced vacuum charge has a screening sign. Screening of a Coulomb impurity in graphene is briefly discussed. We calculate the real vacuum polarization charge density that acquires the quantum electrodynamics vacuum in the supercritical Coulomb potential due to the so-called real vacuum polarization. It is shown that the vacuum charge densities essentially differ in massive and massless cases. We expect that our results can, as a matter of principle, be tested in graphene with a supercritical Coulomb impurity.

hep-th↗

arXiv2016

Vacuum polarization of planar Dirac fermions by a superstrong Coulomb potential

We study the vacuum polarization of planar charged Dirac fermions by a strong Coulomb potential. Induced vacuum charge density is calculated and analyzed at the subcritical and supercritical Coulomb potentials for massless and massive fermions. For the massless case the induced vacuum charge density is localized at the origin when the Coulomb center charge is subcritical while it has a power-law tail when the Coulomb center charge is supercritical. The finite mass contribution into the induced charge due to the vacuum polarization is small and insignificantly distorts the Coulomb potential only at distances of order of the Compton length. The induced vacuum charge has a screening sign. As is known the quantum electrodynamics vacuum becomes unstable when the Coulomb center charge is increased from subcritical to supercritical values. In the supercritical Coulomb potential the quantum electrodynamics vacuum acquires the charge due to the so-called real vacuum polarization. We calculate the real vacuum polarization charge density. Screening of the Coulomb center charge are briefly discussed. We expect that our results will be helpful for more deep understanding of the fundamental problem of quantum electrodynamics and can as a matter of principle be tested in graphene with a supercritical Coulomb impurity.

quant-ph↗

arXiv2015

Vacuum polarization of charged massless fermions in Coulomb and Aharonov--Bohm fields

Vacuum polarization of charged massless fermions is investigated in the superposition of Coulomb and Aharonov--Bohm (AB) potentials in 2+1 dimensions. For this purpose we construct the Green function of the two-dimensional Dirac equation with Coulomb and AB potentials (via the regular and irregular solutions of the radial Dirac equation) and calculate the vacuum polarization charge density in these fields in the so-called subcritical and supercritical regimes. The role of the self-adjoint extension parameter is discussed in terms of the physics of problem. We hope that our results will be helpful in the more deep understanding the fundamental problem of quantum electrodynamics and can be applied to the problems of charged impurity screening in graphene with taking into consideration the electron spin.

cond-mat.mes-hall↗

arXiv2015

Polarization operator in the 2+1 dimensional quantum electrodynamics with a nonzero fermion density in a constant uniform magnetic field

The polarization operator (tensor) for planar charged fermions in constant uniform magnetic field is calculated in the one-loop approximation of the 2+1 dimensional quantum electrodynamics (QED$_{2+1}$) with a nonzero fermion density. We construct the Green function of the Dirac equation with a constant uniform external magnetic field in the QED$_{2+1}$ at the finite chemical potential, find the imaginary part of this Green function and then obtain the polarization tensor related to the combined contribution from real particles occupying the finite number of energy levels and magnetic field. We expect that some physical effects under consideration seem to be likely to be revealed in a monolayer graphene sample in the presence of external constant uniform magnetic field $B$ perpendicular to it.

hep-th↗

arXiv2014

Bound states of massive fermions in the Aharonov--Bohm-like fields

Bound states of massive fermions in the Aharonov-Bohm like fields have analytically been studied. The Hamiltonians with the Aharonov--Bohm like potentials are essentially singular and therefore require specification of a one-parameter self-adjoint extension. We construct self-adjoint Dirac Hamiltonians with the Aharonov-Bohm (AB) potential in 2+1 dimensions that are specified by boundary conditions at the origin. It is of interest that for some range of extension parameter the AB potential can bind relativistic charged massive fermions. The bound-state energy is determined by the AB magnetic flux and depends upon fermion spin and extension parameter; it is a periodical function of the magnetic flux. We also construct self-adjoint Hamiltonians for the so-called Aharonov-Casher (AC) problem, show that nonrelativistic neutral massive fermions can be bound by the Aharonov-Casher background, determine the range of extension parameter in which fermion bound states exist and find their energies as well as wave functions.

quant-ph↗

arXiv2013

Creation of planar charged fermions in Coulomb and Aharonov-Bohm potentials

The creation of charged fermions from the vacuum by a Coulomb field in the presence of an Aharonov--Bohm (AB) potential are studied in 2+1 dimensions. The process is governed by a (singular) Dirac Hamiltonian that requires the supplementary definition in order for it to be treated as a self-adjoint quantum-mechanical operator. By constructing a one-parameter self-adjoint extension of the Dirac Hamiltonian, specified by boundary conditions, we describe the (virtual bound) quasistationary states with "complex energy" emerging in an attractive Coulomb potential, derive for the first time, complex equations (depending upon the electron spin and the extension parameter) for the quasistationary state "complex energy". The constructed self-adjoint Dirac Hamiltonians in Coulomb and AB potentials are applied to provide a correct description to the low-energy electron excitations, as well as the creation of charged quasiparticles from the vacuum in graphene by the Coulomb impurity in the presence of AB potential. It is shown that the strong Coulomb field can create charged fermions for some range of the extension parameter.

hep-ph↗

arXiv2013

Planar massless fermions in Coulomb and Aharonov-Bohm potentials

Solutions to the Dirac equation are constructed for a massless charged fermion in Coulomb and Aharonov--Bohm potentials in 2+1 dimensions. The Dirac Hamiltonian on this background is singular and needs a one-parameter self-adjoint extension, which can be given in terms of self-adjoint boundary conditions. We show that the virtual (quasistationary) bound states emerge in the presence of an attractive Coulomb potential when the so-called effective charges become overcritical and discuss a restructuring of the vacuum of the quantum electrodynamics when the virtual bound states emerge. We derive equations, which determine the energies and lifetimes of virtual bound states, find solutions of obtained equations for some values of parameters as well as analyze the local density of states as a function of energy in the presence of Coulomb and Aharonov--Bohm potentials.

cond-mat.mes-hall↗

arXiv2010

Zero-energy states of fermions in the field of Aharonov--Bohm type in 2+1 dimensions

The quantum-mechanical problem of constructing a self-adjoint Hamiltonian for the Dirac equation in an Aharonov--Bohm field in 2+1 dimensions is solved with taking into account the fermion spin. The one-parameter family of self-adjoint extensions is found for the above Dirac Hamiltonian with particle spin. The correct domain of the self-adjoint Hamiltonian extension selecting by means of acceptable boundary conditions can contain regular and singular (at the point ${\bf r}=0$) square-integrable functions on the half-line with measure $rdr$. We argue that the physical reason of the existence of singular solutions is the additional attractive potential, which appear due to the interaction between the spin magnetic moment of fermion and Aharonov--Bohm magnetic field. For some range of parameters there are bound fermionic states. It is shown that fermion (particle and antiparticle) states with zero energy are intersected what signals on the instability of quantum system and the possibility of a fermion-antifermion pair creation by the static external field.

quant-ph↗

arXiv2010

Free and bound spin-polarized fermions in the fields of Aharonov--Bohm kind

The scattering of electrons by an Aharonov--Bohm field is considered from the viewpoint of quantum-mechanical problem of constructing a self-adjoint Hamiltonian for the Pauli equation. The correct domain for the self-adjoint Hamiltonian, which takes into account explicitly the electron spin is found. A one-parameter self-adjoint extension of the Hamiltonian for spin-polarized electrons in the Aharonov--Bohm field is selected. The correct domain of the self-adjoint Hamiltonian can contain regular and singular (at the point ${\bf r}=0$) square-integrable functions on the half-line with measure $rdr$. We argue that the physical reason of the existence of singular functions is the additional attractive potential, which appear due to the interaction between the spin magnetic moment of fermion and Aharonov--Bohm magnetic field. The scattering amplitude and cross section are obtained for spin-polarized electrons scattered by the Aharonov--Bohm field. It is shown that in some range of the extension parameter there appears a bound state. Since the Hamiltonian of the nonrelativistic Dirac--Pauli equation for a massive neutral fermion with the anomalous magnetic moment (AMM) in the electric field of a linear charge aligned perpendicularly to the fermion motion has the form of the Hamiltonian for the Pauli equation in the Aharonov--Bohm flux tube, we also calculate the scattering amplitude and cross section for the neutral fermion.

quant-ph↗

arXiv2008

Fermion pair production in planar Coulomb and Aharonov--Bohm potentials

Exact analytic solutions are found for the Dirac equation in 2+1 dimensions for a spin-one-half particle in a combination of the Lorentz 3-vector and scalar Coulomb as well as Aharonov--Bohm potentials. We employ the two-component Dirac equation which contains a new parameter introduced by Hagen to describe the spin of the spin-1/2 particle. We derive a transcendental equations that implicitly determine the energy spectrum of an electron near the negative-energy continuum boundary and the critical charges for some electron states. Fermion pair production from a vacuum by a strong Coulomb field in the presence of the magnetic flux tube of zero radius is considered. It is shown that the presence of the Ahanorov--Bohm flux tends to stabilize the system.

hep-th↗

arXiv2007

Scattering of spin-polarized electron in an Aharonov--Bohm potential

The scattering of spin-polarized electrons in an Aharonov--Bohm vector potential is considered. We solve the Pauli equation in 3+1 dimensions taking into account explicitly the interaction between the three-dimensional spin magnetic moment of electron and magnetic field. Expressions for the scattering amplitude and the cross section are obtained for spin-polarized electron scattered off a flux tube of small radius. It is also shown that bound electron states cannot occur in this quantum system. The scattering problem for the model of a flux tube of zero radius in the Born approximation is briefly discussed.

hep-th↗

arXiv2007

Electron bound by a potential well in the presence of a constant uniform magnetic field

We study the effect of a constant uniform magnetic field on an electrically charged massive particle (an electron) bound by a potential well, which is described by means of a single attractive $λδ({\bf r})$ potential. A transcendental equation that determines the electron energy spectrum is derived and solved. The electron wave function in the ground (bound) state is approximately constructed in a remarkable simple form. It is shown that there arises the probability current in the bound state in the presence of a uniform constant magnetic field. This (electric) current, being by the gauge invariant quantity, must be observable and involve (and exercise influence on) the electron scattering. The probability current density resembles a stack of "pancake" vortices'' whose circulating "currents'' around the magnetic field direction ($z$-axes) are mostly confined within the plane $z=0$. We also compute the tunnelling probability of electron from the bound to free state under a weak constant homogeneous electric field, which is parallel to the magnetic field. The model under consideration is briefly discussed in two spatial dimensions.

quant-ph↗