Fall 2026
Time & Location: All talks are on Wednesday in TBA, at 3:00 PM unless otherwise noted.
Organizers: Kalina Mincheva and Alessandra Costantini
Information on up coming events can be found at unofficial seminar website: Here
September 09, 2026
Algebra and Combinatoric
Title: Combinatorial aspects of lattices associated to subspace arrangements arising from group actions
Speaker: Francesca Gandini - St. Olaf College
Abstract: Consider a finite group acting linearly on a vector space. Each group element can be represented as a linear map whose graph is a subspace and the collection of these graphs gives a subspace arrangement. From an algebraic point of view, the vanishing ideal of the union of the subspaces can be used to find generators for the ring of polynomial invariants under the action of the group. Geometrically, we can also study the intersection lattice of the subspace arrangement, which can give cohomological information about the same ideal.
When one considers permutation actions, new combinatorial perspectives on this intersection lattice arise. In particular, for the regular action of the group on itself, the intersection lattice of the subspace arrangement is isomorphic to the coset poset, a known object of study in geometric and topological combinatorics. For other permutation actions, we establish that stabiliser subgroups of orbit partitions and their cosets can be used to label the vertices of the lattice. We then study these lattices with combinatorial techniques and computational tools to better understand the various algebraic structures associated with them.
September 16, 2026
Algebra and Combinatorics
Title: Relations between higher level Hurwitz class numbers.
Speaker: Trinh Le - Tulane university
Abstract: We connect generalizations of the classical Hurwitz class numbers coming from two different frameworks: one introduced by Pei and Wang, arising from the generalized Cohen--Eisenstein series, and another by Li, Skoruppa, and Zhou, arising from Eichler orders of quaternion algebras. As applications, we obtain new basis for Eisenstein space $E_{3/2}^{+}(4N,\mathrm{id})$, a generalization of recent results of Beckwith and Mono, and a generalization of Gauss' formula. This is joint work with Olivia Beckwith.