27,883 research outputs found

    Higher and missing resonances in omega photoproduction

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    We study the role of the nucleon resonances (NN^*) in ω\omega photoproduction by using the quark model resonance parameters predicted by Capstick and Roberts. The employed γNN\gamma N \to N^* and NωNN^* \to \omega N amplitudes include the configuration mixing effects due to the residual quark-quark interactions. The contributions from the nucleon resonances are found to be important in the differential cross sections at large scattering angles and various spin observables. In particular, the parity asymmetry and beam-target double asymmetry at forward scattering angles are suggested for a crucial test of our predictions. The dominant contributions are found to be from N32+(1910)N\frac32^+ (1910), a missing resonance, and N32(1960)N\frac32^- (1960) which is identified as the D13(2080)D_{13}(2080) of the Particle Data Group.Comment: 8 pages, LaTeX with ws-p8-50x6-00.cls, 4 figures (5 eps files), Talk presented at the NSTAR2001 Workshop on the Physics of Excited Nucleons, Mainz, Germany, Mar. 7-10, 200

    Electromagnetic production of vector mesons at low energies

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    We have investigated exclusive photoproduction of light vector mesons (ω\omega, ρ\rho and ϕ\phi) on the nucleon at low energies. In order to explore the questions concerning the so-called missing nucleon resonances, we first establish the predictions from a model based on the Pomeron and meson exchange mechanisms. We have also explored the contributions due to the mechanisms involving ss- and uu-channel intermediate nucleon state. Some discrepancies found at the energies near threshold and large scattering angles suggest a possibility of using this reaction to identify the nucleon resonances.Comment: 9 pages, LaTeX with sprocl.sty, 5 figures (11 eps files), Talk presented at the NSTAR2000 Workshop, The Physics of Excited Nucleons, Jefferson Lab., Newport News, Feb. 16-19, 200

    Higher Derivative CP(N) Model and Quantization of the Induced Chern-Simons Term

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    We consider higher derivative CP(N) model in 2+1 dimensions with the Wess-Zumino-Witten term and the topological current density squared term. We quantize the theory by using the auxiliary gauge field formulation in the path integral method and prove that the extended model remains renormalizable in the large N limit. We find that the Maxwell-Chern-Simons theory is dynamically induced in the large N effective action at a nontrivial UV fixed point. The quantization of the Chern-Simons term is also discussed.Comment: 8 pages, no figure, a minor change in abstract, added Comments on the quantization of the Chern-Simons term whose coefficient is also corrected, and some references are added. Some typos are corrected. Added a new paragraph checking the equivalence between (3) and (5), and a related referenc

    Network analysis of online bidding activity

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    With the advent of digital media, people are increasingly resorting to online channels for commercial transactions. Online auction is a prototypical example. In such online transactions, the pattern of bidding activity is more complex than traditional online transactions; this is because the number of bidders participating in a given transaction is not bounded and the bidders can also easily respond to the bidding instantaneously. By using the recently developed network theory, we study the interaction patterns between bidders (items) who (that) are connected when they bid for the same item (if the item is bid by the same bidder). The resulting network is analyzed by using the hierarchical clustering algorithm, which is used for clustering analysis for expression data from DNA microarrays. A dendrogram is constructed for the item subcategories; this dendrogram is compared with a traditional classification scheme. The implication of the difference between the two is discussed.Comment: 8 pages and 11 figure

    Direct-write, focused ion beam-deposited,7 K superconducting C-Ga-O nanowire

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    We have fabricated C-Ga-O nanowires by gallium focused ion beam-induced deposition from the carbon-based precursor phenanthrene. The electrical conductivity of the nanowires is weakly temperature dependent below 300 K, and indicates a transition to a superconducting state below Tc = 7 K. We have measured the temperature dependence of the upper critical field Hc2(T), and estimate a zero temperature critical field of 8.8 T. The Tc of this material is approximately 40% higher than that of any other direct write nanowire, such as those based on C-W-Ga, expanding the possibility of fabricating direct-write nanostructures that superconduct above liquid helium temperaturesComment: Accepted for AP

    Orbital Magnetism of 2D Chaotic Lattices

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    We study the orbital magnetism of 2D lattices with chaotic motion of electrons withing a primitive cell. Using the temperature diagrammatic technique we evaluate the averaged value and rms fluctuation of magnetic response in the diffusive regime withing the model of non-interacting electrons. The fluctuations of magnetic susceptibility turn out to be large and at low temperature can be of the order of χL(kFl)3/2\chi_{L} (k_{F}l)^{3/2}, where kFk_{F} is the Fermi wavevector, ll is the mean free path, and χL\chi_{L} is the Landau susceptibility. In the certain region of magnetic fields the paramagnetic contribution to the averaged response is field independent and larger than the absolute value of Landau response.Comment: 6 pages, Latex file, figures available upon reques

    Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)

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    We investigated the electronic structures of the two-dimensional layered perovskite Sr2_{2}\textit{M}O4_{4} (\textit{M}=4\textit{d} Ru, 4\textit{d} Rh, and 5\textit{d} Ir) using optical spectroscopy and polarization-dependent O 1\textit{s} x-ray absorption spectroscopy. While the ground states of the series of compounds are rather different, their optical conductivity spectra σ(ω)\sigma(\omega) exhibit similar interband transitions, indicative of the common electronic structures of the 4\textit{d} and 5\textit{d} layered oxides. The energy splittings between the two ege_{g} orbitals, i.e.i.e., d3z2r2d_{3z^{2}-r^{2}} and dx2y2d_{x^{2}-y^{2}}, are about 2 eV, which is much larger than those in the pseudocubic and 3\textit{d} layered perovskite oxides. The electronic properties of the Sr2_{2}\textit{M}O4_{4} compounds are discussed in terms of the crystal structure and the extended character of the 4\textit{d} and 5\textit{d} orbitals
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