Effective Operator Treatment of the Lipkin Model

We analyze the Lipkin Model using effective operator techniques. We present both analytical and numerical results for effective Hamiltonians. The accuracy of the cluster approximation is investigated.Comment: To appear in Phys.Rev.

Diffractive heavy pseudoscalar-meson productions by weak neutral currents

A first theoretical study for neutrino-induced diffractive productions of heavy pseudoscalar-mesons, \eta_c and \eta_b, off a nucleon is performed based on factorization formalism in QCD. We evaluate the forward diffractive production cross section in perturbative QCD in terms of the light-cone wave functions of Z boson and \eta_{c,b} mesons, and the gluon distribution of the nucleon. The diffractive production of \eta_c is governed by the axial vector coupling of the longitudinally polarized Z boson to Q\bar{Q} pair, and the resulting \eta_c production cross section is larger than the J/\psi one by one order of magnitude. The bottomonium \eta_b production, which shows up for higher beam energy, is also discussed.Comment: 5 pages with 3 embedded figures. Talk presented at the 15th International Spin Physics Symposium, Spin 2002, Brookhaven National Laboratory, September 9-14, 200

Structure of the constituent quark and quark distributions of hadrons

We study the structure of constituent quarks by dressing bare quarks with the Goldstone bosons and its implications for quark distribution functions of hadrons $f_1(x)$, $g_1(x)$ and $h_1(x)$. In particular we discuss effects of the dressing on the nucleon spin structure, and find that contributions to chiral-odd $h_1(x)$ is quite different from those to $g_1 (x)$, which can be measured in the semi-inclusive polarized deep inelastic scattering.Comment: 7 pages, LaTeX, 4 figures are included using epsfig.sty, talk presented at QULEN97, to appear in the proceedings, Complete PS fils is also available at http://WWW.physik.tu-muenchen.de/~ksuzuki/publication.htm