5,745 research outputs found
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
Azimuthal Angular Distributions in EDDE as Spin-Parity Analyser and Glueball Filter for LHC
Exclusive Double Diffractive Events (EDDE) are analysed as the source of
information about the central system. Experimental possibilities for exotic
particles searches are considered. From the reggeized tensor current picture
some azimuthal angle dependences were obtained to fit the data from WA102
experiment and to make predictions for LHC collider.Comment: LaTeX, 20 pages, 7 figures, references are adde
Derivative based global sensitivity measures
The method of derivative based global sensitivity measures (DGSM) has
recently become popular among practitioners. It has a strong link with the
Morris screening method and Sobol' sensitivity indices and has several
advantages over them. DGSM are very easy to implement and evaluate numerically.
The computational time required for numerical evaluation of DGSM is generally
much lower than that for estimation of Sobol' sensitivity indices. This paper
presents a survey of recent advances in DGSM concerning lower and upper bounds
on the values of Sobol' total sensitivity indices . Using these
bounds it is possible in most cases to get a good practical estimation of the
values of . Several examples are used to illustrate an
application of DGSM
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