On a construction of self-dual gauge fields in seven dimensions

We consider gauge fields associated with a semisimple Malcev algebra. We construct a gauge-invariant Lagrangian and found a solution of modified Yang-Mills equations in seven dimensions.Comment: 10 pages, LaTeX, no figure

Open shells in reduced-density-matrix-functional theory

Reduced-density-matrix-functional theory is applied to open-shell systems. We introduce a spin-restricted formulation by appropriately expressing approximate correlation-energy functionals in terms of spin-dependent occupation numbers and spin-independent natural orbitals. We demonstrate that the additional constraint of total-spin conservation is indispensable for the proper treatment of open-shell systems. The formalism is applied to the first-row open-shell atoms. The obtained ground-state energies are in very good agreement with the exact values as well as other state of the art quantum chemistry calculationsComment: 4 pages, 2 figures, corrected typo

Self-gravitating stringlike configurations from nonlinear electodynamics

We consider static, cylindrically symmetric configurations in general relativity coupled to nonlinear electrodynamics (NED) with an arbitrary gauge-invariant Lagrangian of the form $L_{em}= \Phi(F)$, $F =F_{mn}F^{mn}$. We study electric and magnetic fields with three possible orientations: radial (R), longitudinal (L) and azimuthal (A), and try to find solitonic stringlike solutions, having a regular axis and a flat metric at large $r$, with a possible angular defect. Assuming the function $\Phi(F)$ to be regular at small $F$, it is shown that a regular axis is impossible in R-fields if there is a nonzero effective electric charge and in A-fields if there is a nonzero effective electric current along the axis. Solitonic solutions are only possible for purely magnetic R-fields and purely electric A-fields, in cases when $\Phi(F)$ tends to a finite limit at large $F$. For both R- and A-fields, the desired large $r$ asymptotic is only possible with a non- Maxwell behaviour of $\Phi(F)$ at small $F$. For L-fields, solutions with a regular axis are easily obtained (and can be found by quadratures) whereas a desired large $r$ asymptotic is only possible in an exceptional solution; the latter gives rise to solitonic configurations in case \Phi(F) = \const \cdot \sqrt{F}. We give an explicit example of such a solution.Comment: 7 pages, Latex-2e,gc.sty, to appear in Grav. & Cosmo

Solution of the Hyperon Puzzle within a Relativistic Mean-Field Model

The equation of state of cold baryonic matter is studied within a relativistic mean-field model with hadron masses and coupling constants depending on the scalar field. All hadron masses undergo a universal scaling, whereas the coupling constants are scaled differently. The appearance of hyperons in dense neutron star interiors is accounted for, however the equation of state remains sufficiently stiff if a reduction of the $\phi$ meson mass is included. Our equation of state matches well the constraints known from analyses of the astrophysical data and the particle production in heavy-ion collisions.Comment: 7 pages, 4 figures; replaced with the published versio

On the Galactic chemical evolution of sulphur. Sulphur abundances from the [S i] 1082 nm line in giants

Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. To contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-LTE insensitive spectral diagnostics in Disk and Halo stars with homogeneously determined stellar parameters. Methods. We derive Teff from photometric colours, logg from stellar isochrones and Bayesian estimation, and [Fe/H] and [S/Fe] from spectrum synthesis. We derive [S/Fe] from the [S i] 1082 nm line in 39 mostly cool and metal-poor giants, using 1D LTE MARCS model atmospheres to model our high-resolution NIR spectra obtained with the VLT, NOT and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 stars. Our results argue for a chemical evolution of sulphur that is typical for alpha-elements, contrary to some previous studies. Our abundances are systematically higher by about 0.1 dex in comparison to other studies that arrived at similar conclusions using other sulphur diagnostics. Conclusions. We find the [S i] line to be a valuable diagnostic of sulphur abundances in cool giants down to [Fe/H] ~ -2.3. We argue that a homogeneous determination of stellar parameters is necessary, since the derived abundances are sensitive to them. Our results ([S/Fe]) show reasonable agreement with predictions of contemporary models of Galactic chemical evolution. In these models sulphur is predominantly created in massive stars by oxygen burning, and ejected in the ISM during Type II SNe explosions. Systematic differences with previous studies likely fall within modelling uncertainties.Comment: 13 pages, 6 figures. Accepted for publication in A&