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.
We introduce some graded versions of the walled Brauer algebra, working over
a field of characteristic zero. This allows us to prove that the walled Brauer
algebra is Morita equivalent to an idempotent truncation of a certain infinite
dimensional version of Khovanov's arc algebra, as suggested by recent work of
Cox and De Visscher. We deduce that the walled Brauer algebra is Koszul
whenever its defining parameter is non-zero.
We show that the algebras describing blocks of the category of cuspidal
weight (respectively generalized weight) $\mathfrak{sl}_n$-modules are
one-parameter (respectively multi-parameter) deformations of certain Brauer
tree algebras. We explicitly determine these deformations both graded and
ungraded. The algebras we deform also appear as special centralizer subalgebras
of Temperley-Lieb algebras or as generalized Khovanov algebras.
A simple, combinatorial construction of the sl(n)-WZNW fusion ring, also
known as Verlinde algebra, is given. As a byproduct of the construction one
obtains an isomorphism between the fusion ring and a particular quotient of the
small quantum cohomology ring of the Grassmannian Gr(k,k+n). We explain how our
approach naturally fits into known combinatorial descriptions of the quantum
cohomology ring, by establishing what one could call a
`Boson-Fermion-correspondence' between the two rings.