3,746 research outputs found
Electrical conductivity of hot Abelian plasma with scalar charge carriers
We study the electrical conductivity of hot Abelian plasma containing scalar
charge carriers in the leading logarithmic order in coupling constant
using the Boltzmann kinetic equation. The leading contribution to the collision
integral is due to the M{\o}ller and Bhabha scattering of scalar particles with
a singular cross section in the region of small momentum transfer. Regularizing
this singularity by taking into account the hard thermal loop corrections to
the propagators of intermediate particles, we derive the second order
differential equation which determines the kinetic function. We solve this
equation numerically and also use a variational approach in order to find a
simple analytical formula for the conductivity. It has the standard parametric
dependence on the coupling constant with the prefactor taking a somewhat lower value compared to
the fermionic case. Finally, we consider the general case of hot Abelian plasma
with an arbitrary number of scalar and fermionic particle species and derive
the simple analytical formula for its conductivity.Comment: 36 pages, 2 figures, 4 table
Supercritical electric dipole and migration of electron wave function in graphene
We study the Dirac equation for quasiparticles in gapped graphene with two
oppositely charged impurities by using the technique of linear combination of
atomic orbitals and variational Galerkin--Kantorovich method. We show that for
sufficiently large charges of impurities the wave function of the occupied
electron bound state of the highest energy changes its localization from the
negatively charged impurity to the positively charged one as the distance
between the impurities increases. This migration of the electron wave function
of supercritical electric dipole is a generalization of the familiar phenomenon
of the atomic collapse of single charged impurity to the case where
electron-hole pairs are spontaneously created from vacuum in bound states with
charge impurities thus partially screening them.Comment: 8 pages, 6 Figures, and video; submitted to Europhysics Letter
Influence of backreaction of electric fields and Schwinger effect on inflationary magnetogenesis
We study the generation of electromagnetic fields during inflation when the
conformal invariance of Maxwell's action is broken by the kinetic coupling
of the electromagnetic field to the inflaton
field . We consider the case where the coupling function
decreases in time during inflation and, as a result, the electric component of
the energy density dominates over the magnetic one. The system of equations
which governs the joint evolution of the scale factor, inflaton field, and
electric energy density is derived. The backreaction occurs when the electric
energy density becomes as large as the product of the slow-roll parameter
and inflaton energy density, .
It affects the inflaton field evolution and leads to the scale-invariant
electric power spectrum and the magnetic one which is blue with the spectral
index for any decreasing coupling function. This gives an upper limit
on the present-day value of observed magnetic fields below .
It is worth emphasizing that since the effective electric charge of particles
is suppressed by the coupling function, the Schwinger effect
becomes important only at the late stages of inflation when the inflaton field
is close to the minimum of its potential. The Schwinger effect abruptly
decreases the value of the electric field, helping to finish the inflation
stage and enter the stage of preheating. It effectively produces the charged
particles, implementing the Schwinger reheating scenario even before the fast
oscillations of the inflaton. The numerical analysis is carried out in the
Starobinsky model of inflation for the powerlike and
Ratra-type coupling functions.Comment: 21 pages, 8 figure
Investigation of the influence of technological conditions of microarc oxidation of magnesium alloys on their structural state and mechanical properties
Наведені дослідження структури і властивостей покриттів, отриманих при мікродуговій обробці на магнієвому сплаві. Обробка проводилася при анодно-катодному режимі в лужному електроліті з різними домішками. Показана можливість формування кристалічних оксидних покриттів різного фазового складу (MgO, MgAl₂O₄, Mg₂Sі₄, Mg₃(PO₄)₂) товщиною до 300 мкм, що мають високу адгезію з основою, гарні захисні властивості і високу твердість, яка досягає 6,6 ГПа
Evolution of the Primordial Axial Charge across Cosmic Times
We investigate collisional decay of the axial charge in an electron-photon
plasma at temperatures 10 MeV - 100 GeV. We demonstrate that the decay rate of
the axial charge is first order in the fine-structure constant and thus orders of magnitude greater than the
naive estimate which has been in use for decades. This counterintuitive result
arises through infrared divergences regularized at high temperature by
environmental effects. The decay of axial charge plays an important role in the
problems of leptogenesis and cosmic magnetogenesis.Comment: 7 pages, 3 figures + Supplementary Material (3 pages
Electron states in the field of charged impurities in two-dimensional Dirac systems
We review the theoretical and experimental results connected with the
electron states in two-dimensional Dirac systems paying a special attention to
the atomic collapse in graphene. Two-electron bound states of a Coulomb
impurity are considered too. A rather subtle role of a magnetic field in the
supercritical charge problem in graphene is discussed. The electron states in
the field of two equally charged impurities are studied and the conditions for
supercritical instability to occur are determined. It is shown that the
supercriticality of novel type is realized in gapped graphene with two unlikely
charged impurities. For sufficiently large charges of impurities, it is found
that the wave function of the occupied electron bound state of the highest
energy changes its localization from the negatively charged impurity to the
positively charged one as the distance between the impurities increases. The
specifics of the atomic collapse in bilayer graphene is considered and it is
shown that the atomic collapse in this material is not related to the
phenomenon of the fall-to-center.Comment: Review Article, 39 pages, 14 figures. arXiv admin note: text overlap
with arXiv:1311.0064, arXiv:1401.5992, arXiv:1611.05221, arXiv:1510.02890,
arXiv:1406.5770 by other author
Problem statement of dynamic creep for isotropic and оrthotropic bodies
Mathematical problem statement of dynamic creep for isotropic and orthotropic bodies is presented in the paper. The cyclic creep-damage theory of Breslavsky-Morachkovsky is used. Numerical methods for the solution of such creep problems is considered, where the mixed variational functional and RFM (Rvachov’s Functions method), or finite element method (FEM), are applied. Numerical results of the creep problem analysis for plate with centered hole under tension are given
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