104 research outputs found

    Perturbative Evolution and Regge Behaviour

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    The known analytic properties of the Compton amplitude at small Q2Q^2 place significant constraints on its behaviour at large Q2Q^2. This calls for a re-evaluation of the role of perturbative evolution in past fits to data.Comment: Revised figures 4 and

    Proton structure function at small Q^2

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    A fit is made to the data for the proton structure function up to Q^2=10 GeV^2, including the real gamma p total cross-section. It is economical and simple, and its form is motivated by physical principles. It is extrapolated down to very small values of x. Data for the ratio (nu W_2^n/nu W_2^p) are also fitted. A FORTRAN program for the fit to (nu W_2^p) is available by email on request Figure 5 from the original version has been deleted.Comment: 10 pages plus 9 figure

    Photon Radiation in a Heat Bath

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    We discuss the bremsstrahlung of photons into a heat bath, and calculate from first principles the energy radiated. Even to lowest order the spectrum of the radiation at low frequency is no more singular than at zero temperature. In addition to the obvious contributions, this spectrum includes terms associated with fluctuations. [Revised version has additional explanations]Comment: 7 pages, plus 2 figures in pictex DAMTP 94/

    Unusual high-pT jet events at HERA

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    We calculate the cross-section for events at HERA where the proton loses only a minute fraction of its initial energy, all of which goes into producing a single pair of transverse jets.Comment: 4 pages plus figure

    QCD Pressure and the Trace Anomaly

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    Exact relations between the QCD thermal pressure and the trace anomaly are derived. These are used, first, to prove the equivalence of the thermodynamic and the hydrodynamic pressure in equilibrium in the presence of the trace anomaly, closing a gap in previous arguments. Second, in the temporal axial gauge a formula is derived which expresses the thermal pressure in terms of a Dyson-resummed two-point function. This overcomes the infrared problems encountered in the conventional perturbation-theory approach.Comment: 9 pages plain te

    Total cross sections

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    Regge theory provides a very simple and economical description of all total cross sectionsComment: 7 pages + 5 figures (appended as a ps file

    The proton's gluon structure

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    The proton's gluon structure function at small x is larger than nowadays is commonly believedComment: Talk at QCD 02, Montpellier, July 200

    Simple Physical Approach to Thermal Cutting Rules

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    A first-principles derivation is given of the imaginary part of a Green's function in real-time thermal field theory. The analysis and its conclusions are simpler than in the usual circled-vertex formalism. The relationship to Cutkosky-like cutting rules is explained.Comment: 9 pages, plain tex, 5 figures embedded with epsf -- 2 typos correcte

    Urgent problems at small x

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    Regge theory provides an excellent fit to small-x structure-function data from Q^2=0 right up to the highest available values, but it also teaches us that conventional approaches to perturbative evolution are incorrect.Comment: Talk at DIS99, Zeuthen, April 1999. 3 pages, latex, 3 figure

    Thermalisation of Longitudinal Gluons

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    In the usual real-time finite-temperature gauge theory both the physical and the unphysical degrees of freedom are thermalised. We discuss the alternative approach where only the physical transverse components of the gauge field have bare thermal propagators, whereas the unphysical degrees of freedom are not heated. We show how pinch singularities are avoided: sometimes this requires resummation. If only the hard thermal loop is included in the resummation, the spatially-longitudinal component of the gauge field, which contains an extra collective plasmon mode, becomes fully thermalised, though the Faddeev-Popov ghost and the remaining unphysical component of the gauge field remain frozen.Comment: 10 pages, 1 figure appended as pictex-file, DAMTP 93-06, TUW-93-0
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