3,949 research outputs found
Coherent and stochastic contributions of compound resonances in atomic processes: Electron recombination, photoionization and scattering
In open-shell atoms and ions, processes such as photoionization, combination
(Raman) scattering, electron scattering and recombination, are often mediated
by many-electron compound resonances. We show that their interference
(neglected in the independent-resonance approximation) leads to a coherent
contribution, which determines the energy-averaged total cross sections of
electron- and photon-induced reactions obtained using the optical theorem. In
contrast, the partial cross sections (e.g., electron recombination, or photon
Raman scattering) are dominated by the stochastic contributions. Thus, the
optical theorem provides a link between the stochastic and coherent
contributions of the compound resonances. Similar conclusions are valid for
reactions via compound states in molecules and nuclei
Electric dipole moment of the electron in YbF molecule
Ab initio calculation of the hyperfine, P-odd, and P,T-odd constants for the
YbF molecule was performed with the help of the recently developed technique,
which allows to take into account correlations and polarization in the
outercore region. The ground state electronic wave function of the YbF molecule
is found with the help of the Relativistic Effective Core Potential method
followed by the restoration of molecular four-component spinors in the core
region of ytterbium in the framework of a non-variational procedure. Core
polarization effects are included with the help of the atomic Many Body
Perturbation Theory for Yb atom. For the isotropic hyperfine constant A,
accuracy of our calculation is about 3% as compared to the experimental datum.
The dipole constant Ad (which is much smaller in magnitude), though better than
in all previous calculations, is still underestimated by almost 23%. Being
corrected within a semiempirical approach for a perturbation of 4f-shell in the
core of Yb due to the bond making, this error is reduced to 8%. Our value for
the effective electric field on the unpaired electron is 4.9 a.u.=2.5E+10 V/cm.Comment: 7 pages, REVTE
Electron recombination, photoionization and scattering via many-electron compound resonances
Highly excited eigenstates of atoms and ions with open f shell are chaotic
superpositions of thousands, or even millions of Hartree-Fock determinant
states. The interaction between dielectronic and multielectronic configurations
leads to the broadening of dielectronic recombination resonances and relative
enhancement of photon emission due to opening of thousands of radiative decay
channels. The radiative yield is close to 100% for electron energy . 1 eV and
rapidly decreases for higher energies due to opening of many autoionization
channels. The same mechanism predicts suppression of photoionization and
relative enhancement of the Raman scattering. Results of our calculations of
the recombination rate are in agreement with the experimental data for W20+ and
Au25+.Comment: Physical Review
Accurate relativistic many-body calculations of van der Waals coefficients C_8 and C_10 for alkali-metal dimers
We consider long-range interactions between two alkali-metal atoms in their
respective ground states. We extend the previous relativistic many-body
calculations of C_6 dispersion coefficients [Phys.Rev. Lett. {\bf 82}, 3589
(1999)] to higher-multipole coefficients C_8 and C_10. A special attention is
paid to usually omitted contribution of core-excited states. We calculate this
contribution within relativistic random-phase approximation and demonstrate
that for heavy atoms core excitations contribute as much as 10% to the
dispersion coefficients. We tabulate results for both homonuclear and
heteronuclear dimers and estimate theoretical uncertainties. The estimated
uncertainties for C_8 coefficients range from 0.5% for Li_2 to 4% for Cs_2.Comment: 12 pages, submitted to Journal of Chemical Physic
Zero-energy peak of the density of states and localization properties of a one-dimensional Frenkel exciton: Off-diagonal disorder
We study a one-dimensional Frenkel Hamiltonian with off-diagonal disorder,
focusing our attention on the physical nature of the zero-energy peak of the
density of states. The character of excitonic states (localized or delocalized)
is also examined in the vicinity of this peak. It is shown that the state being
responsible for the peak is localized. A detailed comparison of the
nearest-neighbor approach with the long-range dipole-dipole coupling is
performed.Comment: 15 pages with 7 figures (REVTeX). To appear in Physical Review
Geostrophic tripolar vortices in a two-layer fluid : linear stability and nonlinear evolution of equilibria
We investigate equilibrium solutions for tripolar vortices in a two-layer quasi-geostrophic flow. Two of the vortices are like-signed and lie in one layer. An opposite-signed vortex lies in the other layer. The families of equilibria can be spanned by the distance (called separation) between the two like-signed vortices. Two equilibrium configurations are possible when the opposite-signed vortex lies between the two other vortices. In the first configuration (called ordinary roundabout), the opposite signed vortex is equidistant to the two other vortices. In the second configuration (eccentric roundabouts), the distances are unequal. We determine the equilibria numerically and describe their characteristics for various internal deformation radii. The two branches of equilibria can co-exist and intersect for small deformation radii. Then, the eccentric roundabouts are stable while unstable ordinary roundabouts can be found. Indeed, ordinary roundabouts exist at smaller separations than eccentric roundabouts do, thus inducing stronger vortex interactions. However, for larger deformation radii, eccentric roundabouts can also be unstable. Then, the two branches of equilibria do not cross. The branch of eccentric roundabouts only exists for large separations. Near the end of the branch of eccentric roundabouts (at the smallest separation), one of the like-signed vortices exhibits a sharp inner corner where instabilities can be triggered. Finally, we investigate the nonlinear evolution of a few selected cases of tripoles.PostprintPeer reviewe
Systematic limits on sin^2{2theta_{13}} in neutrino oscillation experiments with multi-reactors
Sensitivities to sin^2{2theta_{13}} without statistical errors (``systematic
limit'') are investigated in neutrino oscillation experiments with multiple
reactors. Using an analytical approach, we show that the systematic limit on
sin^2{2theta_{13}} is dominated by the uncorrelated systematic error sigma_u of
the detector. Even in an experiment with multi-detectors and multi-reactors, it
turns out that most of the systematic errors including the one due to the
nature of multiple sources is canceled as in the case with a single reactor
plus two detectors, if the near detectors are placed suitably. The case of the
KASKA plan (7 reactors and 3 detectors) is investigated in detail, and it is
explicitly shown that it does not suffer from the extra uncertainty due to
multiple reactors.Comment: 26 pages, 10 eps-files, revtex
Geostrophic tripolar vortices in a two-layer fluid: Linear stability and nonlinear evolution of equilibria
Enhanced sensitivity to time-variation of m_p/m_e in the inversion spectrum of ammonia
We calculate the sensitivity of the inversion spectrum of ammonia to possible
time-variation of the ratio of the proton mass to the electron mass,
mu=m_p/m_e. For the inversion transition (lambda= 1.25 cm^{-1}) the relative
frequency shift is significantly enhanced: delta(omega)/omega=-4.46,
delta(mu)/mu. This enhancement allows one to increase sensitivity to the
time-variation of mu using NH_3 spectra for high redshift objects. We use
published data on microwave spectra of the object B0218+357 to place the limit
delta(mu)/mu =(0.6 +/- 1.9) 10^{-6} at redshift z=0.6847; this limit is several
times better than the limits obtained by different methods and may be
significantly improved. Assuming linear time dependence we obtain
dot{mu}/mu=(-1 +/- 3) 10^{-16} yr^{-1}
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