24,208 research outputs found

    Diffraction and Low-Q^2 Physics Including Two-Photon Physics

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    Recent experimental results on the partonic structure of the photon and on the color singlet exchange in strong interaction processes are reviewed. At the LEP electron-positron and HERA lepton-proton colliders, complementary and consistent measurements have been achieved on the quark-gluon structure of quasi-real and virtual photons. At the HERA lepton-proton and Tevatron proton-antiproton colliders, the quark-gluon configuration of the diffractive exchange is consistently found to have a large gluon component. The rate of diffractive interactions observed by the HERA and Tevatron experiments, however, is largely different and challenges explanation (invited plenary talk at the XXIX International Conference on High Energy Physics, Vancouver, B.C. Canada (1998)).Comment: 36 pages (Latex), 35 figures (Postscript); in this replaced version the report on 'Structure Functions' by A.T.Doyle has been taken out and is available in hep-ex/981202

    Weighted Surface Algebras

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    A finite-dimensional algebra AA over an algebraically closed field KK is called periodic if it is periodic under the action of the syzygy operator in the category of AAA-A- bimodules. The periodic algebras are self-injective and occur naturally in the study of tame blocks of group algebras, actions of finite groups on spheres, hypersurface singularities of finite Cohen-Macaulay type, and Jacobian algebras of quivers with potentials. Recently, the tame periodic algebras of polynomial growth have been classified and it is natural to attempt to classify all tame periodic algebras. We introduce the weighted surface algebras of triangulated surfaces with arbitrarily oriented triangles and describe their basic properties. In particular, we prove that all these algebras, except the singular tetrahedral algebras, are symmetric tame periodic algebras of period 44. Moreover, we describe the socle deformations of the weighted surface algebras and prove that all these algebras are symmetric tame periodic algebras of period 44. The main results of the paper form an important step towards a classification of all periodic symmetric tame algebras of non-polynomial growth, and lead to a complete description of all algebras of generalized quaternion type. Further, the orbit closures of the weighted surface algebras (and their socle deformations) in the affine varieties of associative KK-algebra structures contain wide classes of tame symmetric algebras related to algebras of dihedral and semidihedral types, which occur in the study of blocks of group algebras with dihedral and semidihedral defect groups

    On Ext(2) between Weyl modules for quantum GL(n)

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