71 research outputs found
Mixed ladder determinantal varieties from two-sided ladders
We study the family of ideals defined by mixed size minors of two-sided
ladders of indeterminates. We compute their Groebner bases with respect to a
skew-diagonal monomial order, then we use them to compute the height of the
ideals. We show that these ideals correspond to a family of irreducible
projective varieties, that we call mixed ladder determinantal varieties. We
show that these varieties are arithmetically Cohen-Macaulay. We characterize
the arithmetically Gorenstein ones, among those that satisfy a technical
condition. Our main result consists in proving that mixed ladder determinantal
varieties belong to the same G-biliaison class of a linear variety.Comment: 15 pages, contains an improved version of Theorem 1.25 (now 1.23
Distributive Lattices, Affine Semigroups, and Branching Rules of the Classical Groups
We study algebras encoding stable range branching rules for the pairs of
complex classical groups of the same type in the context of toric degenerations
of spherical varieties. By lifting affine semigroup algebras constructed from
combinatorial data of branching multiplicities, we obtain algebras having
highest weight vectors in multiplicity spaces as their standard monomial type
bases. In particular, we identify a family of distributive lattices and their
associated Hibi algebras which can uniformly describe the stable range
branching algebras for all the pairs we consider.Comment: 30 pages, extensively revise
The nullcone in the multi-vector representation of the symplectic group and related combinatorics
We study the nullcone in the multi-vector representation of the symplectic
group with respect to a joint action of the general linear group and the
symplectic group. By extracting an algebra over a distributive lattice
structure from the coordinate ring of the nullcone, we describe a toric
degeneration and standard monomial theory of the nullcone in terms of double
tableaux and integral points in a convex polyhedral cone.Comment: 21 pages, v2: title changed, typos and errors correcte
- …