1,846 research outputs found
Angular distribution of high-energy photoproduction close to the end of spectrum
We consider the differential cross section of electron-positron pair
production by a high-energy photon in a strong Coulomb field close to the end
of the electron or positron spectrum. When the momentum transfer largely
exceeds the electron mass, the cross section is obtained analytically in a
compact form. Coulomb corrections essentially modify the cross section even for
moderate values of the nuclear charge number . In the same kinematical
region, the angular distribution for bound-free pair production,
bremsstrahlung, and photorecombination is also obtained.Comment: 12 pages, 4 figure
High-energy photoproduction cross section close to the end of spectrum
We consider the cross section of electron-positron pair production by a
high-energy photon in a strong Coulomb field close to the end of electron or
positron spectrum. We show that the cross section essentially differs from the
result obtained in the Born approximation as well as form the result which
takes into account the Coulomb corrections under assumption that both electron
and positron are ultrarelativistic. The cross section of bremsstrahlung in a
strong Coulomb field by a high-energy electron is also obtained in the region
where the final electron is not ultrarelativistic.Comment: 20 pages, 4 figure
The Induced Charge Generated By The Potential Well In Graphene
The induced charge density, , generated in graphene by the
potential well of the finite radius is considered. The result for
is derived for large distances . We also obtained
the induced charges outside of the radius and inside of this radius
for subcritical and supercritical regimes. The consideration is based on the
convenient representation of the induced charge density via the Green's
function of electron in the field.Comment: 12 pages, 2 figures, version published in Phys.Rev.
Screening of Coulomb Impurities in Graphene
We calculate exactly the vacuum polarization charge density in the field of a
subcritical Coulomb impurity, , in graphene. Our analysis is based on
the exact electron Green's function, obtained by using the operator method, and
leads to results that are exact in the parameter , where is
the "fine structure constant" of graphene. Taking into account also
electron-electron interactions in the Hartree approximation, we solve the
problem self-consistently in the subcritical regime, where the impurity has an
effective charge , determined by the localized induced charge. We find
that an impurity with bare charge Z=1 remains subcritical, , for any , while impurities with and higher can become
supercritical at certain values of .Comment: 4 pages, 2 figure
Coulomb corrections to the Delbrueck scattering amplitude at low energies
In this article, we study the Coulomb corrections to the Delbrueck scattering
amplitude. We consider the limit when the energy of the photon is much less
than the electron mass. The calculations are carried out in the coordinate
representation using the exact relativistic Green function of an electron in a
Coulomb field. The resulting relative corrections are of the order of a few
percent for scattering on for a large charge of the nucleus. We compare the
corrections with the corresponding ones calculated through the dispersion
integral of the pair production cross section and also with the magnetic loop
contribution to the g-factor of a bound electron. The last one is in a good
agreement with our results but the corrections calculated through the
dispersion relation are not.Comment: 8 pages, 6 figure
Nature of the Darwin term and contribution to the Lamb shift for an arbitrary spin of the nucleus
The contact Darwin term is demonstrated to be of the same origin as the
spin-orbit interaction. The correction to the Lamb shift,
generated by the Darwin term, is found for an arbitrary nonvanishing spin of
the nucleus, both half-integer and integer. There is also a contribution of the
same nature to the nuclear quadrupole moment.Comment: 9 pages, latex, no figure
Induced Current and Aharonov-Bohm Effect in Graphene
The effect of vacuum polarization in the field of an infinitesimally thin
solenoid at distances much larger than the radius of solenoid is investigated.
The induced charge density and induced current are calculated. Though the
induced charge density turned out to be zero, the induced current is finite
periodical function of the magnetic flux . The expression for this
function is found exactly in a value of the flux. The induced current is equal
to zero at the integer values of as well as at half-integer
values of this ratio, where is the elementary magnetic
flux. The latter is a consequence of the Furry theorem and periodicity of the
induced current with respect to magnetic flux. As an example we consider the
graphene in the field of solenoid perpendicular to the plane of a sample.Comment: 3 pages, 1 figure, version accepted to Phys. Rev.
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