7,901 research outputs found
Coupled-cluster single-double calculations of the relativistic energy shifts in C IV, Na I, Mg II, Al III, Si IV, Ca II and Zn II
The relativistic coupled-cluster single-double method is used to calculate
the dependence of frequencies of strong -transitions in many monovalent
atoms and ions on the fine-structure constant . These transitions are
used in the search for manifestations of the variation of the fine-structure
constant in quasar absorption spectra. Results of the present calculations are
in good agreement with previous calculations but are more accurate.Comment: 6 pages, 4 tables, no figures; submitted to Phys. Rev.
Evolution strategies applied to the problem of line profile decomposition in QSO spectra
We describe the decomposition of QSO absorption line ensembles applying an
evolutionary forward modelling technique. The modelling is optimized using an
evolution strategy (ES) based on a novel concept of completely derandomized
self-adaption. The algorithm is described in detail. Its global optimization
performance in decomposing a series of simulated test spectra is compared to
that of classical deterministic algorithms. Our comparison demonstrates that
the ES is a highly competitive algorithm capable to calculate the optimal
decomposition without requiring any particular initialization.Comment: 9 pages, 5 figures, accepted for publication in Astron. Astrophys.,
corrected figure misplacements, full resolution manuscript can be obtained at
http://www.hs.uni-hamburg.de/EN/Ins/Per/Quast
Combining real and virtual Higgs boson mass constraints
Within the framework of the standard model we observe that there is a
significant discrepancy between the most precise boson decay asymmetry
measurement and the limit from direct searches for Higgs boson production.
Using methods inspired by the Particle Data Group we explore the possible
effect on fits of the Higgs boson mass. In each case the central value and the
95% confidence level upper limit increase significantly relative to the
conventional fit. The results suggest caution in drawing conclusions about the
Higgs boson mass from the existing data.Comment: 11 pages, Latex. Citations are added and paper is otherwise
reconciled with version to be published in Physical Review Letter
HE 0515-4414 - an unusual sub-damped Ly alpha system revisited
Using STIS and VLT UVES observations we have examined the ionization,
abundances, and differential dust depletion of metals, the kinematic structure,
and the physical conditions in the molecular hydrogen-bearing sub-damped Ly
alpha system toward HE 0515-4414 at z = 1.15. The velocity interval of
associated metal lines extends for 700 km/s. In addition, saturated H I
absorption is detected in the blue damping wing of the main component. The
column density ratios of associated Al II, Al III, and Fe II lines indicate
that the absorbing material is ionized. 19 of in total 31 detected metal line
components are formed within peripheral H II regions, while only 12 components
are associated with the predominantly neutral main absorber. For the main
absorber the observed abundance ratios of refractory elements to Zn range from
Galactic warm disk [Si/Zn] = - 0.40, [Fe/Zn] = -1.10 to halo-like and
essentially undepleted patterns. The dust-corrected metal abundances indicate a
nucleosynthetic odd-even effect and might imply an anomalous depletion of Si
relative to Fe for two components, but otherwise do correspond to solar ratios.
The intrinsic average metallicity is almost solar [Fe/H] = -0.08, whereas the
uncorrected average is [Zn/H] = -0.38. The ion abundances in the periphery
conform with solar element composition. The detection of H II as well as the
large variation in dust depletion for this sight line raises the question
whether in future studies of damped Ly alpha systems ionization and depletion
effects have to be considered in further detail. Ionization effects, for
instance, may pretend an enrichment of alpha elements. An empirical recipe for
detecting H II regions is provided.Comment: 26 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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