54,276 research outputs found

    Color dipole cross section and inelastic structure function

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    Instead of starting from a theoretically motivated form of the color dipole cross section in the dipole picture of deep inelastic scattering, we start with a parametrization of the deep inelastic structure function for electromagnetic scattering with protons, and then extract the color dipole cross section. Using the parametrizations of F2(ξ=x or W2,Q2)F_2(\xi=x \ {\rm or}\ W^2,Q^2) by Donnachie-Landshoff and Block et al., we find the dipole cross section from an approximate form of the presumed dipole cross section convoluted with the perturbative photon wave function for virtual photon splitting into a color dipole with massless quarks. The color dipole cross section determined this way reproduces the original structure function within about 10\% for 0.10.1 GeV2≤Q2≤10^2\leq Q^2\leq 10 GeV2^2. We discuss the large and small form of the dipole cross section and compare with other parameterizations.Comment: 11 pages, 12 figure

    Nonleptonic two-body charmless B decays involving a tensor meson in the Perturbative QCD Approach

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    Two-body charmless hadronic B decays involving a light tensor meson in the final states are studied in the perturbative QCD approach based on kTk_T factorization. From our calculations, we find that the decay branching ratios for color allowed tree-dominated decays B→a20π+B\to a_{2}^{0}\pi^{+} and B→a2−π+B\to a_{2}^{-}\pi^{+} modes are of order 10−610^{-6} and 10−510^{-5}, respectively. While other color suppressed tree-dominated decays have very small branching ratios. In general, the branching ratios of most decays are in the range of 10−510^{-5} to 10−810^{-8}, which are bigger by one or two orders of magnitude than those predictions obtained in Isgur-Scora-Grinstein-Wise II model and in the covariant light-front approach, but consistent with the recent experimental measurements and the QCD factorization calculations. Since the decays with a tensor meson emitted from vacuum are prohibited in naive factorization, the contributions of nonfactorizable and annihilation diagrams are very important to these decays, which are calculable in our perturbative QCD approach. We also give predictions to the direct CP asymmetries, some of which are large enough for the future experiments to measure. Because we considered the mixing between f2f_{2} and f2′f_{2}', the decay rates are enhanced significantly for some decays involving f2′f_{2}^{\prime} meson, even with a small mixing angle.Comment: 26 pages, 2 figure

    Path integral Monte Carlo study of the interacting quantum double-well model: Quantum phase transition and phase diagram

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    The discrete time path integral Monte Carlo (PIMC) with a one-particle density matrix approximation is applied to study the quantum phase transition in the coupled double-well chain. To improve the convergence properties, the exact action for a single particle in a double well potential is used to construct the many-particle action. The algorithm is applied to the interacting quantum double-well chain for which the zero-temperature phase diagram is determined. The quantum phase transition is studied via finite-size scaling and the critical exponents are shown to be compatible with the classical two-dimensional (2D) Ising universality class -- not only in the order-disorder limit (deep potential wells) but also in the displacive regime (shallow potential wells).Comment: 17 pages, 7 figures; Accepted for publication in Phys. Rev.
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