3,427 research outputs found
Calculation of hyperfine structure constants for ytterbium
We calculate energies and hyperfine structure constants A and B for low-lying
levels of Yb. The latter is treated as a two-electron atom. To account
for valence-valence correlations the configuration interaction method is used.
Valence-core correlations are accounted for within the many-body perturbation
theory which is used to construct effective two-electron operators in the
valence space.Comment: 8 pages, latex, iopart class or ioplppt style, submitted to J. Phys.
Cooper pairing of electrons and holes in graphene bilayer: Correlation effects
Cooper pairing of spatially separated electrons and holes in graphene bilayer
is studied beyond the mean-field approximation. Suppression of the screening at
large distances, caused by appearance of the gap, is considered
self-consistently. A mutual positive feedback between appearance of the gap and
enlargement of the interaction leads to a sharp transition to correlated state
with greatly increased gap above some critical value of the coupling strength.
At coupling strength below the critical, this correlation effect increases the
gap approximately by a factor of two. The maximal coupling strength achievable
in experiments is close to the critical value. This indicated importance of
correlation effects in closely-spaced graphene bilayers at weak substrate
dielectric screening. Another effect beyond mean-field approximation considered
is an influence of vertex corrections on the pairing, which is shown to be very
weak.Comment: 6 pages, 5 figures; some references were adde
Calculation of francium hyperfine anomaly
The Dirac-Hartree-Fock plus many-body perturbation theory (DHF+MBPT) method
has been used to calculate hyperfine structure constants for Fr. Calculated
hyperfine structure anomaly for hydrogen-like ion has been shown to be in good
agreement with analytical expressions. It has been shown that the ratio of the
anomalies for and states is weakly dependent on the principal
quantum number. Finally, we estimate Bohr--Weisskopf corrections for several Fr
isotopes. Our results may be used to improve experimental accuracy for the
nuclear factors of short-lived isotopes.Comment: 5 pages, 3 tables, 2 figures. arXiv admin note: text overlap with
arXiv:1703.1004
Bragg Reflection Waveguide: Anti-Mirror Reflection and Light Slowdown
The effect of the light group velocity reduction in dielectric Bragg
reflection waveguide structures (SiO/TiO) in the vicinity of the cutoff
frequency is studied experimentally. The effect of anti-mirror reflection,
specific for the Bragg reflection waveguides, is described and employed for
detection of "slow light". The experiments were performed with the use of the
Ti:sapphire laser pulses ~ 100 fs in length. The group index 30 with
a fractional pulse delay (normalized to the pulse width) of 10 is
demonstrated. The problems and prospects of implementation of the slow-light
devices based on the Bragg reflection waveguide structures are discussed.Comment: 11 pages, in the previous version, we failed to insert figure
Bose-Einstein correlations at LEP and Tevatron energies
Using the Bose-Einstein correlations (BEC) implemented in PYTHIA we
investigated a possibility of the CDF experiment at the Tevatron to see the
two-particle correlations in the final state of interactions. The approach
based on quantum field theory at finite temperature was applied to the ALEPH
data at LEP, and the BEC important parameters were retrieved.Comment: 5 pages, 4 figures, 1 table. Based on the talk gived at The 6th
international workshop on very high multiplicity physics, JINR Dubna, 16-17
april 2005. In Table 1. the sign of error adde
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