Ben Webster

  1. Quiver Schur algebras and q-Fock space.

    Authors: Ben Webster, Catharina Stroppel
    Subjects: Rings and Algebras
    Abstract

    We develop a graded version of the theory of cyclotomic q-Schur algebras, in
    the spirit of the work of Brundan-Kleshchev on Hecke algebras and of Ariki on
    q-Schur algebras. As an application, we identify the coefficients of the
    canonical basis on a higher level Fock space with q-analogues of the
    decomposition numbers of cyclotomic q-Schur algebras.

  2. Knot invariants and higher representation theory II: the categorification of quantum knot invariants.

    Authors: Ben Webster
    Subjects: Geometric Topology
    Abstract

    We construct knot invariants categorifying the quantum knot variants for all
    representations of quantum groups. We show that these invariants coincide with
    previous invariants defined by Khovanov for sl_2 and sl_3 and by
    Mazorchuk-Stroppel and Sussan for sl_n. We also suggest an approach to showing
    that these knot homologies are functorial. Our technique uses categorifications
    of the tensor products of integrable representations of Kac-Moody algebras and
    quantum groups, constructed a prequel to this paper.

  3. Knot invariants and higher representation theory.

    Authors: Ben Webster
    Subjects: Geometric Topology
    Abstract

    We construct knot invariants categorifying the quantum knot variants for all
    representations of quantum groups. We show that these invariants coincide with
    previous invariants defined by Khovanov for sl(2) and sl(3) and by
    Mazorchuk-Stroppel and Sussan for sl(n). We also suggest an approach to showing
    that these knot homologies are functorial.

  4. The geometry of Markov traces.

    Authors: Ben Webster, Geordie Williamson
    Subjects: Algebraic Geometry
    Abstract

    We give a geometric interpretation of the Jones-Ocneanu trace on the Hecke
    algebra, using the equivariant cohomology of sheaves on SL(n). This
    construction makes sense for all simple groups, so we obtain a generalization
    of the Jones-Ocneanu trace to Hecke algebras of other types. We show that this
    trace coincides with a trace defined by Gomi using Lusztig's Fourier transform,
    and give a short geometric proof of Gomi's expansion of this trace in terms of
    characters.

  5. Singular blocks of parabolic category O and finite W-algebras.

    Authors: Ben Webster
    Subjects: Representation Theory
    Abstract

    We show that each integral block of parabolic category O (including singular
    ones) for a semi-simple Lie group can be realized as a full subcategory of a
    ``thick'' category O over a finite W-algebra for the same Lie group.

    The nilpotent used to construct this finite W-algebra is determined by the
    central character of the block, and the subcategory taken is that killed by a
    two-sided ideal depending on the original parabolic. The equivalences in
    question are induced by those of Milicic-Soergel and Skryabin.

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