1,746 research outputs found
Radiative corrections and parity nonconservation in heavy atoms
The self-energy and the vertex radiative corrections to the effect of parity
nonconservation in heavy atoms are calculated analytically in orders Z alpha^2
and Z^2 alpha^3 ln(lambda_C/r_0), where lambda_C and r_0 being the Compton
wavelength and the nuclear radius, respectively. The value of the radiative
correction is -0.85% for Cs and -1.41% for Tl. Using these results we have
performed analysis of the experimental data on atomic parity nonconservation.
The obtained values of the nuclear weak charge,
Q_W=-72.90(28)_{exp}(35)_{theor} for Cs, and Q_W=-116.7(1.2)_{exp}(3.4)_{theor}
for Tl, agree with predictions of the standard model. As an application of our
approach we have also calculated analytically dependence of the Lamb shift on
the finite nuclear size.Comment: 4 pages, 4 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.
Bremsstrahlung in alpha-Decay Reexamined
A high-statistics measurement of bremsstrahlung emitted in the alpha decay of
210Po has been performed, which allows to follow the photon spectra up to
energies of ~ 500 keV. The measured differential emission probability is in
good agreement with our theoretical results obtained within the quasi classical
approximation as well as with the exact quantum mechanical calculation. It is
shown that due to the small effective electric dipole charge of the radiating
system a significant interference between the electric dipole and quadrupole
contributions occurs, which is altering substantially the angular correlation
between the alpha particle and the emitted photon.Comment: 10 pages, 5 figures, v2: fix of small typo
Virtual light-by-light scattering and the g factor of a bound electron
The contribution of the light-by-light diagram to the g factor of electron
and muon bound in Coulomb field is obtained. For electron in a ground state,
our results are in good agreement with the results of other authors obtained
numerically for large Z. For relatively small Z our results have essentially
higher accuracy as compared to the previous ones. For muonic atoms, the
contribution is obtained for the first time with the high accuracy in whole
region of Z.Comment: 10 pages, 3 figures, RevTe
Corrections to deuterium hyperfine structure due to deuteron excitations
We consider the corrections to deuterium hyperfine structure originating from
the two-photon exchange between electron and deuteron, with the deuteron
excitations in the intermediate states. In particular, the motion of the two
intermediate nucleons as a whole is taken into account. The problem is solved
in the zero-range approximation. The result is in good agreement with the
experimental value of the deuterium hyperfine splitting.Comment: 7 pages, LaTe
Charge asymmetry in the differential cross section of high-energy e+e- photoproduction in the field of a heavy atom
First quasiclassical correction to the differential cross section of
high-energy electron-positron photoproduction in the electric field of a heavy
atom is obtained with the exact account of the field. This correction is
responsible for the charge asymmetry in this process. When the
transverse momentum of at least one of the produced particles is much larger
than the electron mass , the charge asymmetry can be as large as tens
percent. We also estimate the contribution to the charge
asymmetry coming from the Compton-type diagram. For heavy nuclei, this
contribution is negligible. For light nuclei, is noticeable
only when the angle between the momenta of electron and positron is of order of
( is the photon energy) while the transverse momenta of both
particles are much larger than .Comment: 19 pages, 7 figure
An integral method for solving nonlinear eigenvalue problems
We propose a numerical method for computing all eigenvalues (and the
corresponding eigenvectors) of a nonlinear holomorphic eigenvalue problem that
lie within a given contour in the complex plane. The method uses complex
integrals of the resolvent operator, applied to at least column vectors,
where is the number of eigenvalues inside the contour. The theorem of
Keldysh is employed to show that the original nonlinear eigenvalue problem
reduces to a linear eigenvalue problem of dimension .
No initial approximations of eigenvalues and eigenvectors are needed. The
method is particularly suitable for moderately large eigenvalue problems where
is much smaller than the matrix dimension. We also give an extension of the
method to the case where is larger than the matrix dimension. The
quadrature errors caused by the trapezoid sum are discussed for the case of
analytic closed contours. Using well known techniques it is shown that the
error decays exponentially with an exponent given by the product of the number
of quadrature points and the minimal distance of the eigenvalues to the
contour
Spectroscopic Temperature Determination of Degenerate Fermi Gases
We suggest a simple method for measuring the temperature of ultra-cold gases
made of fermions. We show that by using a two-photon Raman probe, it is
possible to obtain lineshapes which reveal properties of the degenerate sample,
notably its temperature . The proposed method could be used with identical
fermions in different hyperfine states interacting via s-wave scattering or
identical fermions in the same hyperfine state via p-wave scattering. We
illustrate the applicability of the method in realistic conditions for Li
prepared in two different hyperfine states. We find that temperatures down to
0.05 can be determined by this {\it in-situ} method.Comment: 7 pages, 4 figures, Revtex
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