A Higgs Boson Composed of Gauge Bosons

It is proposed to replace the Higgs boson of the standard model by a Lorentz- and gauge-invariant combination of SU(2) gauge bosons. A pair of Higgs bosons is identified with pairs of gauge bosons by setting their mass Lagrangians equal to each other. That immediately determines the mass of the composite Higgs boson. It becomes simply half of the vacuum expectation value of the standard Higgs boson, which matches the observed mass with tree-level accuracy (2%). The two parameters of the standard Higgs potential are replaced by five one-loop self-interactions of the SU(2) gauge bosons, derived from the fundamental gauge couplings. The Brout-Englert-Higgs mechanism of spontaneous symmetry breaking is generalized from scalars to vectors. Their transverse components acquire finite vacuum expectation values which generate masses for both gauge bosons and the Higgs boson. This concept leads beyond the standard model by enabling calculations of the Higgs mass and its potential without adjustable parameters. It can be applied to non-abelian gauge theories in general, such as grand unified models and supersymmetry.Comment: 27 pages, 10 figures, added appendix, fixed errors and typos, clarified the text, added explanation of Equation (15), added reference

Structure and energetics of Si(111)-(5x2)-Au

We propose a new structural model for the Si(111)-(5x2)-Au reconstruction. The model incorporates a new experimental value of 0.6 monolayer for the coverage of gold atoms, equivalent to six gold atoms per 5x2 cell. Five main theoretical results, obtained from first-principles total-energy calculations, support the model. (1) In the presence of silicon adatoms the periodicity of the gold rows spontaneously doubles, in agreement with experiment. (2) The dependence of the surface energy on the adatom coverage indicates that a uniformly covered phase is unstable and will phase-separate into empty and covered regions, as observed experimentally. (3) Theoretical scanning tunneling microscopy images are in excellent agreement with experiment. (4) The calculated band structure is consistent with angle-resolved photoemission spectra; analysis of their correspondence allows the straightforward assignment of observed surface states to specific atoms. (5) The calculated activation barrier for diffusion of silicon adatoms along the row direction is in excellent agreement with the experimentally measured barrier.Comment: 11 pages, 7 figures, also available with higher-resolution figures from http://cst-www.nrl.navy.mil/users/erwin/ausi111.v5.pd

Surface and Grain Boundary Analysis of High Temperature Superconductors

The purpose of this paper is to survey the methods that are available for probing surfaces and grain boundaries of high temperature superconductors. Various surface-sensitive spectroscopies are applied to the analysis of YBa2Cu3O7-x and Bi2Sr2CaCu2O8+x including photoelectron spectroscopy, spatially-resolved electron energy loss spectroscopy, and scanning electron microscopy (SEM). One of the major sources of contamination at surfaces and grain boundaries is found to be BaCO3. The cleavage surface of single crystal Bi2Sr2CaCu2O8+x is inert and can be used to probe bulk properties of superconductors, even with surface-sensitive techniques. The orbital character of the superconducting oxygen 2p holes is found to be Px,y, with x,y in the a,b plane. Photoemission at the Fermi level indicates a Fermi liquid nature of these states

Unoccupied states in Cu and Zn octaethyl-porphyrin and phthalocyanine

Copper and zinc phthalocyanines and porphyrins are used in organic light emitting diodes and dye-sensitized solar cells. Using near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the Cu 2p and Zn 2p edges, the unoccupied valence states at the Cu and Zn atoms are probed and decomposed into 3d and 4s contributions with the help of density functional calculations. A comparison with the N 1s edge provides the 2p states of the N atoms surrounding the metal, and a comparison with inverse photoemission provides a combined density of states.This work was supported by the NSF (Award Nos. CHE-1026245 and DMR-0537588 (SRC)) and by the DOE (Contract Nos. DE-FG02-01ER45917 (end station) and DE-AC03-76SF00098 (ALS)). J.M.G.L. and A.R. acknowledge financial support from Spanish MEC (FIS2007-65702-C02-01), ACI-Promociona (ACI2009-1036), Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-319-07), the European Union through the FP7 e-I3 ETSF (Contract No. 211956), and THEMA (Contract No. 228539) projects.Peer Reviewe