Jochen Bartels

Publications (7)0 Total impact

• Article: Double-logarithms in Einstein-Hilbert gravity and supergravity

  Jochen Bartels, Lev N. Lipatov, Agustin Sabio Vera
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  ABSTRACT: We study the interplay between graviton reggeization and double-logarithmic in energy contributions to four-graviton scattering in theories with and without supersymmetry. Predictions to all orders in the gravitational coupling are given for these double-logarithms. As the number of supersymmetries grows these terms generate a convergent behaviour for the amplitudes at very high energies. At two-loop level, we find agreement with previous exact results for N=8 supergravity and with those of Boucher-Veronneau and Dixon, who studied the N=4,5,6 supergravities using a conjectured double-copy structure of gravity.
  08/2012;
• Source

  Available from: ArXiv

  Article: Twist expansion of the nucleon structure functions, F2 and FL, in the DGLAP improved saturation model

  Jochen Bartels, Krzysztof Golec-Biernat, Leszek Motyka
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  ABSTRACT: Higher twist effects in the deeply inelastic scattering are studied. We start with a short review of the theoretical results on higher twists in QCD. Within the saturation model we perform a twist analysis of the nucleon structure functions FT and FL at small value of the Bjorken variable x. The parameters of the model are fitted to the HERA F2 data, and we derive a prediction for the longitudinal structure function FL. We conclude that for FL the higher twist corrections are sizable whereas for F2 = FT + FL there is a nearly complete cancellation of twist-4 corrections in FT and FL. We discuss a few consequences for future LHC measurements. Comment: 27 pages, 11 figures
  11/2009;
• Source

  Available from: Krzysztof Kutak

  Article: What HERA may provide ?

  Hannes Jung, Albert De Roeck, Jochen Bartels, Olaf Behnke, Johannes Blumlein, Stanley Brodsky, Amanda Cooper-Sarkar, Michal Deak, Robin Devenish, Markus Diehl, [......], Leif Lonnblad, Leszek Motyka, Paul R. Newman, Fred Olness, Daniel Pitzl, Marta Ruspa, Agustin Sabio Vera, Gavin P Salam, Thomas Schorner-Sadenius, Mark Strikman
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  ABSTRACT: More than 100 people participated in a discussion session at the DIS08 workshop on the topic What HERA may provide. A summary of the discussion with a structured outlook and list of desirable measurements and theory calculations is given.
  10/2008;
• Source

  Available from: Jeppe Rosenkrantz Andersen

  Article: Small x Phenomenology - summary of the 3rd Lund Small x Workshop in 2004

  The Small x Collaboration, Jeppe R. Andersen Serguei Baranov, Jochen Bartels, Gergely G. Barnafoldi, Grigorios Chachamis, John Collins, Guenter Grindhammer, Goesta Gustafson, Magnus Hansson, Gunnar Ingelman, [......], Michael Lublinsky, Giuseppe Marchesini, Izabela Milcewicz, Christiane Risler, Agustin Sabio Vera, Malin Sjoedahl, Anna Stasto, Jacek Turnau, Graeme Watt, Nikolai Zotov
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  ABSTRACT: A third workshop on small-x physics, within the Small-x Collaboration, was held in Hamburg in May 2004 with the aim of overviewing recent theoretical progress in this area and summarizing the experimental status. Comment: Edited by: Goesta Gustafson, Hannes Jung, Leif Joensson, Leif Loennblad
  04/2006;
• Source

  Available from: arxiv.org

  Article: $\gamma^* \gamma^*$ Scattering via Secondary Reggeon Exchange in QCD

  Jochen Bartels, Michael Lublinsky
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  ABSTRACT: We summarize the results on the high energy behavior of quark-antiquark exchange in $\gamma^* \gamma^*$ elastic scattering. The ladder diagrams, summed in the double logarithmic approximation, provide a perturbative QCD model for secondary reggeon exchange. Comment: 14 pages, 5 figures, invited review for Modern Physics Letters A
  06/2004;
• Source

  Available from: arxiv.org

  Article: Factorization of Twist-Four Gluon Operator Contributions

  Jochen Bartels, Claas Bontus, Hubert Spiesberger
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  ABSTRACT: We consider diagrams with up to four t-channel gluons in order to specify gluonic twist-four contributions to deep inelastic structure functions. This enables us to extend the method developed by R.K.Ellis, W.Furmanski, and R.Petronzio (EFP) to the gluonic case. The method is based on low-order Feynman diagrams in combination with a dimensional analysis. It results in explicitly gauge invariant expressions for the factorization of twist-four gluon-operator matrix elements and the corresponding coefficient functions.
  09/1999;
• Source

  Available from: ArXiv

  Article: An Estimate of Twist-Four Contributions at Small x and Low Q^2

  Jochen Bartels, Claas Bontus
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  ABSTRACT: We present a first study of gluonic twist-four corrections to the deep inelastic structure function F_2 at small x and small Q^2. The calculations are based upon the double logarithmic approximation of the coupled twist-four evolution equations of the gluonic twist-four operators that are expected to be dominant at small x. We first review the analytical results which are presently available and define the framework of our calculation. In the second part we discuss the connection with DIS diffractive dissociation which can be used to estimate the size of some of the twist-four corrections. In the final part we show, for three different choices of the input distributions, the relative magnitude of the leading-twist and the twist-four contributions. Comment: 46 pages, 17 figures, 5 tables, LaTeX, AMSMath, requires bm.sty
  06/1999;