13,337 research outputs found

    Low-energy expansion of the pion-nucleon Lagrangian

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    The renormalized pion-nucleon Lagrangian is calculated to O(p^3) in heavy baryon chiral perturbation theory. By suitably chosen transformations of the nucleon field, the Lagrangian is brought to a standard form.Comment: 10 pages, Latex, 1 figure in uuencoded postscript file embedded with epsfig.st

    Four-pion production

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    Starting from the low-energy structure derived from QCD, we extend the amplitudes for four-pion production in e+ e- annihilation and tau decays up to invariant four-pion masses of 1 GeV. Cross sections and branching ratios BR(rho^0 -> 4 pi) are compared with available data.Comment: 4 pages, 3 figures, contribution to Proc. of QCD'02, Montpellier, July 2002, misprints correcte

    Firewalls: A Balance Between Security and Accesibility

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    Access control lists and firewall rules are intended to prevent access to certain resources on a computer network while allowing access to other resources. Access control lists determine who has access to resources while firewall rules prevent general access to resources. The goal of this research is to find the best way to optimize a campus internet connection as well as a balance between the application of rules and lists and the accessibility of the outside world. This research is done utilizing a simulated internet and local network environment. The environment utilized simulates the set-up currently in use by an educational institution and will serve as a test environment upon completion of my research

    Quantum Chromodynamics

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    After a brief historical review of the emergence of QCD as the quantum field theory of strong interactions, the basic notions of colour and gauge invariance are introduced leading to the QCD Lagrangian. The second lecture is devoted to perturbative QCD, from tree-level processes to higher-order corrections in renormalized perturbation theory, including jet production in e+ e- annihilation, hadronic tau decays and deep inelastic scattering. The final two lectures treat various aspects of QCD beyond perturbation theory. The main theme is effective field theories, from heavy quarks to the light quark sector where the spontaneously broken chiral symmetry of QCD plays a crucial role.Comment: 48 pages, 28 figures. Lectures given at the 2005 European School of High-Energy Physics, Kitzbuehel, Austria, Aug. 21 - Sept. 3, 2005; to appear in the Proceedings (CERN Yellow Report

    Rare Kaon Decays Revisited

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    We present an updated discussion of K\ra\pi \bar{l} l decays in a combined framework of chiral perturbation theory and Large--NcN_c QCD, which assumes the dominance of a minimal narrow resonance structure in the invariant mass dependence of the lˉl \bar{l} l pair. The proposed picture reproduces very well, both the experimental K^+\ra\pi^+ e^+ e^- decay rate and the invariant e+e−e^+ e^- mass spectrum. The predicted Br(K_S\ra\pi^0 e^+ e^-) is, within errors, consistent with the recently reported result from the NA48 collaboration. Predictions for the K\ra\pi \mu^{+}\mu^{-} modes are also obtained. We find that the resulting interference between the {\it direct} and {\it indirect} CP--violation amplitudes in K_L\ra\pi^0 e^+ e^- is constructive
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