Network analysis of online bidding activity

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

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

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

Electromagnetic production of vector mesons at low energies

We have investigated exclusive photoproduction of light vector mesons ($\omega$, $\rho$ and $\phi$) 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 $s$- and $u$-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 and missing resonances in omega photoproduction

We study the role of the nucleon resonances ($N^*$) in $\omega$ photoproduction by using the quark model resonance parameters predicted by Capstick and Roberts. The employed $\gamma N \to N^*$ and $N^* \to \omega N$ 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 $N\frac32^+ (1910)$, a missing resonance, and $N\frac32^- (1960)$ which is identified as the $D_{13}(2080)$ 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

Electronic States in Diffused Quantum Wells

In the present study we calculate the energy values and the spatial distributions of the bound electronic states in some diffused quantum wells. The calculations are performed within the virtual crystal approximation, $sp^3 s^*$ spin dependent empirical tight-binding model and the surface Green function matching method. A good agreement is found between our results and experimental data obtained for AlGaAs/GaAs quantum wells with thermally induced changes in the profile at the interfaces. Our calculations show that for diffusion lengths $L_{D}=20\div100$ {\AA} the transition (C3-HH3) is not sensitive to the diffusion length, but the transitions (C1-HH1), (C1-LH1), (C2-HH2) and (C2-LH2) display large "blue shifts" as L_{D} increases. For diffusion lengths $L_{D}=0\div20$ {\AA} the transitions (C1-HH1) and (C1-LH1) are less sensitive to the L_{D} changes than the (C3-HH3) transition. The observed dependence is explained in terms of the bound states spatial distributions.Comment: ReVTeX file, 7pp., no macros, 4 figures available on the reques

Absorption cross section in the topologically massive gravity at the critical point

The absorption cross section for the the warped AdS$_3$ black hole background shows that it is larger than the area even if the s-wave limit is considered. It raises some question whether the deviation from the areal cross section is due to the warped configuration of the geometry or the rotating coordinate system, where these two effects are mixed up in the warped AdS$_3$ black hole. So, we study the low-frequency scattering dynamics of propagating scalar fields under the warped AdS$_3$ background at the critical point which reduces to the BTZ black hole in the rotating frame without the warped factor, which shows that the deformation effect at the critical point does not appear.Comment: 12 pages, LaTe

Entanglement between qubits induced by a common environment with a gap

We study a system of two qubits interacting with a common environment, described by a two-spin boson model. We demonstrate two competing roles of the environment: inducing entanglement between the two qubits and making them decoherent. For the environment of a single harmonic oscillator, if its frequency is commensurate with the induced two-qubit coupling strength, the two qubits could be maximally entangled and the environment could be separable. In the case of the environment of a bosonic bath, the gap of its spectral density function is essential to generate entanglement between two qubits at equilibrium and for it to be used as a quantum data bus.Comment: accepted for publication in Physical Review