Particle Theory Group
Institute for Theoretical Physics
University of Leipzig
High energy scattering in Quantum Chromodynamics
We study the behaviour of scattering amplitudes in the Regge asymptotics, where the c.m. energy is large compared to all masses and momentum transfers. If there is a second momentum scale, large compared to the hadronic scale but much smaller than the energy, then essential features of the scattering process can be calculated perturbatively. Semi-hard processes are an interesting field of phenomenology. Deep-inelastic scattering at small values of the Bjorken variable is the prominent example, which attracts much attention in connection whith the experiments at HERA.
The high-energy effective action has been shown to be a uselful tool for analyzing the Regge asymptotics in gauge theories. This action describes the scattering of partons by the exchange of reggeized quaks and gluons. The reggeon interaction exhibits remarkable symmetry properties. Interacting reggeons can be treated as integrable spin chains.
Some reviews:
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L.N. Lipatov, Small-x physics in pert. QCD, Phys. Reports 286 (1997) 131, ps file hep-ph/9610276
R. Kirschner, Small-x physics, Zakopane school 1995, Acta Physica Polonica B26 (1995),1961,
J.R. Forshaw and D.A. Ross, Quantum Chromodynamics and the Pomeron, Cambridge Univ. Press 1997.
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Some recent results:
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The effective action has been extended to non-leading gluonic reggeons.
authors: R. Kirschner, L. Szymanowski
The aymptotics of polarized structure functions related to the transversity distributions of quarks and of gluons have been analysed.
authors: B. Ermolaev, R. Kirschner, L. Szymanowski; R. Kirschner, L. Mankiewicz, A. Schäfer, L. Szymanowski
The helicity flip amplitudes of semi-hard diffractive electroproduction of vector mesons has been calculated. There are significant helicity non-conservation effects measurable in current HERA experiments.
authors: D.Yu. Ivanov, R. Kirschner
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For references please consult SPIRES at SLAC or at DESY.
Collaboration and related research groups:
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L.N. Lipatov (St. Petersburg), L. Szymanowski (Warsaw), D.Yu. Ivanov (Novosibirsk).
J. Bartels (Hamburg Univ., DESY), J. Blumlein (DESY-Zeuthen), M. Ciafaloni (Firenze), V.S. Fadin (Novosibirsk), J.Kwiecinski (Cracow), G. Marchesini (Milano), A.H. Mueller (Columbia Univ.), A. White (Argonnne).
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Financial support (beyond University budget):
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Deutsche Forschungsgemeinschaft, post-doc position 1997, 1999-2000.
German Bundesministerium f. Forschung und Technologie, BMBF, Projektträger HEP, post doc position 1997-98.
BMBF, Polish-German agreement on scientific and technological collaboration, travel support Warsaw-Leipzig, 1996-1999.
Volkswagen-Stiftung, travel support St. Petersburg - Leipzig, Warsaw - Leipzig, 1996-1998.
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