Ferromagnetic Kondo-Lattice Model

We present a many-body approach to the electronic and magnetic properties of the (multiband) Kondo-lattice model with ferromagnetic interband exchange. The coupling between itinerant conduction electrons and localized magnetic moments leads, on the one hand, to a distinct temperature-dependence of the electronic quasiparticle spectrum and, on the other hand, to magnetic properties, as e.~g.the Curie temperature T_C or the magnon dispersion, which are strongly influenced by the band electron selfenergy and therewith in particular by the carrier density. We present results for the single-band Kondo-lattice model in terms of quasiparticle densities of states and quasiparticle band structures and demonstrate the density-dependence of the self-consistently derived Curie temperature. The transition from weak-coupling (RKKY) to strong-coupling (double exchange) behaviour is worked out. The multiband model is combined with a tight-binding-LMTO bandstructure calculation to describe real magnetic materials. As an example we present results for the archetypal ferromagnetic local-moment systems EuO and EuS. The proposed method avoids the double counting of relevant interactions and takes into account the correct symmetry of atomic orbitals.Comment: 15 pages, 10 figure

Radiatively Induced Neutrino Masses and Large Higgs-Neutrino Couplings in the Standard Model with Majorana Fields

The Higgs sector of the Standard Model with one right-handed neutrino per family is systematically analyzed. In a model with intergenerational independent mixings between families, we can account for very light neutrinos acquiring Majorana masses radiatively at the first electroweak loop level. We also find that in such a scenario the Higgs coupling to the light-heavy neutrinos and to the heavy-heavy ones may be remarkably enhanced with significant implications for the production of these heavy neutrinos at high energy colliders.Comment: Making the text of an old paper electronically availabl

Review of the k-Body Embedded Ensembles of Gaussian Random Matrices

The embedded ensembles were introduced by Mon and French as physically more plausible stochastic models of many--body systems governed by one--and two--body interactions than provided by standard random--matrix theory. We review several approaches aimed at determining the spectral density, the spectral fluctuation properties, and the ergodic properties of these ensembles: moments methods, numerical simulations, the replica trick, the eigenvector decomposition of the matrix of second moments and supersymmetry, the binary correlation approximation, and the study of correlations between matrix elements.Comment: Final version. 29 pages, 4 ps figures, uses iopart.st

New Fermions at e+^+e−^- Colliders: I. Production and Decay

We analyze the production in $e^+e^-$ collisions of new heavy fermions stemming from extensions of the Standard Model. We write down the most general expression for the production of two heavy fermions and their subsequent decays, allowing for the polarization of the e$^+$e$^-$ initial state and taking into account the final polarization of the fermions. We then discuss the various decay modes including cascade and three body decays, and the production mechanisms, both pair production and single production in association with ordinary fermions.Comment: 21 pages (no figures), Preprint UdeM-LPN-TH-93-15

WormBase 2007

WormBase (www.wormbase.org) is the major publicly available database of information about Caenorhabditis elegans, an important system for basic biological and biomedical research. Derived from the initial ACeDB database of C. elegans genetic and sequence information, WormBase now includes the genomic, anatomical and functional information about C. elegans, other Caenorhabditis species and other nematodes. As such, it is a crucial resource not only for C. elegans biologists but the larger biomedical and bioinformatics communities. Coverage of core areas of C. elegans biology will allow the biomedical community to make full use of the results of intensive molecular genetic analysis and functional genomic studies of this organism. Improved search and display tools, wider cross-species comparisons and extended ontologies are some of the features that will help scientists extend their research and take advantage of other nematode species genome sequences

Quark-hadron-duality in the charmonium and upsilon system

In this work we discuss the practical and conceptual issues related to quark-hadron-duality in heavy-heavy systems. Recent measurements in the charmonium region allow a direct test of quark-hadron-duality. We present a formula for non-resonant background production in e^+ e^- \to D{\bar D} and extract the resonance parameters of the \psi(3S)-\psi(6S). The obtained results are used to investigate the upsilon energy range.Comment: 21 pages, 3 figures, references adde

Rigorous QCD-Potential for the ttˉt\bar{t}-System at Threshold

Recent evidence for the top mass in the region of 160 $GeV$ for the first time provides an opportunity to use the full power of relativistic quantum field theoretical methods, available also for weakly bound systems. Because of the large decay width \G of the top quark individual energy-levels in "toponium" will be unobservable. However, the potential for the $t\bar{t}$ system, based on a systematic expansion in powers of the strong coupling constant \a_s can be rigorously derived from QCD and plays a central role in the threshold region. It is essential that the neglect of nonperturbative (confining) effects is fully justified here for the first time to a large accuracy, also just {\it because} of the large \G. The different contributions to that potential are computed from real level corrections near the bound state poles of the $t\bar{t}$-system which for \G \ne 0 move into the unphysical sheet of the complex energy plane. Thus, in order to obtain the different contributions to that potential we may use the level corrections at that (complex) pole. Within the relevant level shifts we especially emphasize the corrections of order O(\a_s^4 m_t) and numerically comparable ones to that order also from electroweak interactions which may become important as well.Comment: 36 pages (mailer uncorrupted version), TUW-94-1