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[en] An attempt is made for a new type of analysis of the time-variability of the fine-structure constant trying to fit the most recent result from the laboratory measurements, the Oklo constraint and the data from the QSO absorption lines all in consistency with the accelerating universe
[en] Resummation of the perturbative series for the amplitude of lepton pair production in nucleus-nucleus collisions is performed based on the Watson theorem and the hypothesis of infrared stability. An explicit expression for this amplitude is obtained, which is valid to within terms of the ninth order in the fine structure constant.
[en] The optical spectra of objects classified as QSOs in the Sloan Digital Sky Survey Data Release 6 are analyzed with the aim of determining the value of the fine structure constant in the past and then checked for possible changes in the constant over cosmological timescales. The analysis is done by measuring the position of the fine structure lines of the [O III] doublet (λλ4959 and λλ5008) in QSO nebular emission. From the sample of QSOs at redshifts z < 0.8, a sub sample was selected on the basis of the amplitude and width of the [O III] lines. Two different methods were used to determine the position of the lines of the [O III] doublet, both giving similar results. Using a clean sample containing 1568 of such spectra, a value of Δα/α = (+2.4 ± 2.5) x 10-5 (in the range of redshifts z ∼ 0-0.8) was determined. The use of a larger number of spectra allows a factor ∼5 improvement on previous constraints based on the same method. On the whole, we find no evidence of changes in α on such cosmological timescales. The mean variation compatible with our results is 1/(t)Δα/α = (+0.7 ± 0.7) x 10-14 yr-1. The analysis was extended to the [Ne III] and [S II] doublets, although their usefulness is limited due to the fact that all these doublets in QSOs tend to be fainter than [O III], and that some of them are affected by systematics.
[en] The essay gives arguments for deriving the electromagnetic fine structure constant from maximally symmetric spaces. A connection between the order of some subgroups of the monster simple group, the ratio of the proton mass to the electron mass and the fine structure constant is found. A derivation of the fine structure constant from the number of elements in the Cristoffel symbol and the order of the reflection group F4 is given
[en] High-resolution photoionization experiments were carried out with beams of C III, N IV, and O V containing roughly equal amounts of ground-state and metastable ions. The energy scales of the experiments are calibrated with uncertainties of 1 to 10 meV depending on photon energy. These data favorably compare with state-of-the-art R-matrix calculations carried out on an energy grid with a spacing of 13.6 μeV
[en] The radiation emitted from a high-current wall-stabilized arc operated in helium with some admixture of CO2 has been studied. Intensities of fine structure components for 10 multiplets of neutral oxygen (O I) have been determined applying the emission method. On the basis of measured line intensities relative line strengths within each studied multiplet have been obtained. The results are compared with data resulting from the LS-coupling scheme and with other theoretical as well as experimental results available in literature
[en] Building on previous work on the critical behaviour in gravitational collapse of the self-gravitating SU(2) σ-field and using high precision numerical methods we uncover a fine structure hidden in a narrow window of parameter space. We argue that this numerical finding has a natural explanation within a dynamical system framework of critical collapse
[en] High-resolution imaging observations from the Hinode spacecraft in the Ca II H line are employed to study the dynamics of the chromosphere above a sunspot. We find that umbral flashes and other brightenings produced by the oscillation are extremely rich in fine structure, even beyond the resolving limit of our observations (0.''22). The umbra is tremendously dynamic to the point that our time cadence of 20 s does not suffice to resolve the fast lateral (probably apparent) motion of the emission source. Some bright elements in our data set move with horizontal propagation speeds of 30 km s-1. We have detected filamentary structures inside the umbra (some of which have a horizontal extension of ∼1500 km) which, to our best knowledge, had not been reported before. The power spectra of the intensity fluctuations reveal a few distinct areas with different properties within the umbra that seem to correspond with the umbral cores that form it. Inside each one of these areas the dominant frequencies of the oscillation are coherent, but they vary considerably from one core to another.