Isospin Splitting in the Pion-Nucleon Couplings from QCD Sum Rules

We use QCD sum rules for the three point function of a pseudoscalar and two nucleonic currents in order to estimate the charge dependence of the pion nucleon coupling constant coming from isospin violation in the strong interaction. The effect can be attributed primarily to the difference of the quark condensates and . Assuming that the pi0 is a pure isostate we obtain for the splitting between the coupling of proton and neutron to the neutral pion an interval of [0.008 ; 0.023], the uncertainties coming mainly from the input parameters. In order to obtain the coupling to a physical pi0 we have to take pi - eta mixing into account leading to an interval of [0.012 ; 0.037]. The charged pion nucleon coupling is found to be the average of the two neutral ones. Electromagnetic effects are not included.Comment: contributed talk at CIPANP97 (Big Sky, Montana); 3 pages (aipproc.sty), no figure

Axial current matrix elements and pentaquark decay widths in chiral soliton models

Here I explain why in chiral soliton models the hadronic transition operator of the pentaquark decay cannot be identified from the axial current.Comment: seven pages, note on Delta resonance added, refs updated, version to be published in PR

Injury of Aboriginal and Torres Strait Islander people due to transport: 2005-06 to 2009-10

This report looks at death and serious injury of Aboriginal and Torres Strait Islander people in Australia due to transport accidents in the five-year period 2005-06 to 2009-10. Land transport accidents accounted for 26% of all fatal injury cases and 9% of all serious injury cases for Aboriginal and Torres Strait Islander people. The age-standardised rate for Aboriginal and Torres Strait Islander people was 2.8 times the rate for Other Australians for fatal cases, and 1.3 times the rate for Other Australians for serious injuries

Mesons and the Structure of Nucleons

The role of mesons, particularly the pion, in the structure of nucleons is reviewed and investigated. Since quark-antiquark pairs are likely to ``transform" into mesons at large distances, mesons are expected to contribute to nucleon structure. Their effects on the Gottfried sum rule, on the strangeness content of the nucleon, and on the spin of the nucleon are discussed.Comment: 15 pages, TeX file followed by 3 uuencoded PostScript figures (optional), DOE/ER/40427-08-N9

Housing and the Great Recession : a VAR accounting exercise

We use a vector autoregression (VAR) for the components of gross domestic product (GDP) to conduct some sectoral and temporal accounting for the current recession. It is obvious that housing played an important role in the current recession, but residential investment declined for two years before GDP declined. According to the VAR, the level of GDP in the second quarter of 2009---the trough of the decline in GDP---was close to but above the level implied by the estimated sequence of VAR innovations to residential investment over the period 2006:Q1--2009:Q2. Until late 2007 other offsetting shocks kept real GDP growing roughly at trend, but after that the other shocks disappeared or reversed sign. Taking a similar approach with employment, we first observe that, as with output, employment in the housing industry began to fall well before aggregate employment. However, unlike output, the eventual decline in aggregate employment dwarfed the decline in housing-industry employment. The shock to residential construction employment can nonetheless explain a small portion of the current employment shortfall relative to trend.Labor market ; Housing ; Recessions

Isospin-breaking two-nucleon force with explicit Delta-excitations

We study the leading isospin-breaking contributions to the two-nucleon two-pion exchange potential due to explicit Delta degrees of freedom in chiral effective field theory. In particular, we find important contributions due to the delta mass splittings to the charge symmetry breaking potential that act opposite to the effects induced by the nucleon mass splitting.Comment: 10 pages, 4 figure

Novel Properties of Frustrated Low Dimensional Magnets with Pentagonal Symmetry

In the context of magnetism, frustration arises when a group of spins cannot find a configuration that minimizes all of their pairwise interactions simultaneously. We consider the effects of the geometric frustration that arises in a structure having pentagonal loops. Such five-fold loops can be expected to occur naturally in quasicrystals, as seen for example in a number of experimental studies of surfaces of icosahedral alloys. Our model considers classical vector spins placed on vertices of a subtiling of the two dimensional Penrose tiling, and interacting with nearest neighbors via antiferromagnetic bonds. We give a set of recursion relations for this system, which consists of an infinite set of embedded clusters with sizes that increase as a power of the golden mean. The magnetic ground states of this fractal system are studied analytically, and by Monte Carlo simulation.Comment: 7 pages, 7 figures, contribution to ICQ11 (Sapporo, Japan 2010) conference proceeding

Depleted pyrochlore antiferromagnets

I consider the class of "depleted pyrochlore" lattices of corner-sharing triangles, made by removing spins from a pyrochlore lattice such that every tetrahedron loses exactly one. Previously known examples are the "hyperkagome" and "kagome staircase". I give criteria in terms of loops for whether a given depleted lattice can order analogous to the kagome \sqrt{3} \times \sqrt{three} state, and also show how the pseudo-dipolar correlations (due to local constraints) generalize to even the random depleted case.Comment: 6pp IOP latex, 1 figure; Proc. "Highly Frustrated Magnetism 2008", Sept 2008, Braunschwei