On the Nature of the Binary Components of RX J0806.3+1527

We present imaging circular polarimetry and near-infrared photometry of the suspected ultra-short period white-dwarf binary RX J0806.3+1527 obtained with the ESO VLT and discuss the implications for a possible magnetic nature of the white dwarf accretor and the constraints derived for the nature of the donor star. Our V-filter data show marginally significant circular polarization with a modulation amplitude of ~0.5% typical for cyclotron emission from an accretion column in a magnetic field of order 10 MG and not compatible with a direct-impact accretor model. The optical to near-infrared flux distribution is well described by a single blackbody with temperature kT_bb = 35000 K and excludes a main-sequence stellar donor unless the binary is located several scale heights above the galactic disk population.Comment: 2 pages including 2 figures. To appear in RevMexAA(SC) Conference Series, Proc. of IAU Colloquium 194 `Compact Binaries in the Galaxy and Beyond', La Paz (Mexico), eds. G. Tovmassian & E. Sio

On finite volume effects in the chiral extrapolation of baryon masses

We perform an analysis of the QCD lattice data on the baryon octet and decuplet masses based on the relativistic chiral Lagrangian. The baryon self energies are computed in a finite volume at next-to-next-to-next-to leading order (N$^3$LO), where the dependence on the physical meson and baryon masses is kept. The number of free parameters is reduced significantly down to 12 by relying on large-$N_c$ sum rules. Altogether we describe accurately more than 220 data points from six different lattice groups, BMW, PACS-CS, HSC, LHPC, QCDSF-UKQCD and NPLQCD. Values for all counter terms relevant at N$^3$LO are predicted. In particular we extract a pion-nucleon sigma term of 39$_{-1}^{+2}$ MeV and a strangeness sigma term of the nucleon of $\sigma_{sN} = 84^{+ 28}_{-\;4}$ MeV. The flavour SU(3) chiral limit of the baryon octet and decuplet masses is determined with $(802 \pm 4)$ MeV and $(1103 \pm 6)$ MeV. Detailed predictions for the baryon masses as currently evaluated by the ETM lattice QCD group are made.Comment: 44 pages, 10 figures and 6 tables - the revised manuscript contains the results of additional fits at the N^2LO level - 4 additional figures show the size of finite volume corrections for each lattice point - more technical details on the evaluation of finite volume effects are give

Self-dual Yang-Mills fields in pseudoeuclidean spaces

The self-duality Yang-Mills equations in pseudoeuclidean spaces of dimensions $d\leq 8$ are investigated. New classes of solutions of the equations are found. Extended solutions to the D=10, N=1 supergravity and super Yang-Mills equations are constructed from these solutions.Comment: 9 pages, LaTeX, no figure

Two-band ferromagnetic Kondo-lattice model for local-moment half-metals

We introduce a two-band Kondo-lattice model to describe ferromagnetic half-metals with local magnetic moments. In a model study, the electronic and magnetic properties are presented by temperature dependent magnetization curves, band-structures, spin polarizations and plasma frequencies. These are obtained from numerically evaluated equations, based on the single-electron Green functions. We show that the mutual influence between the itinerant electrons and the local magnetic moments is responsible for several phase transitions of the half-metals, namely first and second order magnetic phase transitions, as well as half-metal to semiconductor and half-metal to semimetal transitions.Comment: 10 pages, 5 figures, submitted to Journal of Physics: Condensed Matte

Zero-Mode Dynamics of String Webs

At sufficiently low energy the dynamics of a string web is dominated by zero modes involving rigid motion of the internal strings. The dimension of the associated moduli space equals the maximal number of internal faces in the web. The generic web moduli space has boundaries and multiple branches, and for webs with three or more faces the geometry is curved. Webs can also be studied in a lift to M-theory, where a string web is replaced by a membrane wrapped on a holomorphic curve in spacetime. In this case the moduli space is complexified and admits a Kaehler metric.Comment: LaTeX, 17 pages, 5 eps figures; v2: references adde