Georgia Institute of Technology College of Sciences

Given a finite set of points $\Gamma$ in $\mathbb{P}^n$, we say that $\Gamma$ satisfies the Cayley-Bacharach condition with respect to degree r polynomials, or is CB(r), if any degree r homogeneous polynomial F vanishing on all but one point of $\Gamma$ must vanish at the last point. In recent literature, the condition has played an important role in computing a birational invariant called the degree of irrationality of complex projective varieties. However, the condition itself has not been studied extensively, and surprisingly little is known about the geometric properties of CB(r) points. 

In this talk, I will discuss a new combinatorial approach to the study of the CB(r) condition, using matroid theory, and present some examples of how matroid theory can shed light on the underlying geometry of such sets.
 

The theory of stable polynomials features a key notion called proper position, which generalizes interlacing of real-rooted polynomials to higher dimensions. In a recent paper, I introduced a Lorentzian analog of proper position and used it to give a new characterization of elementary quotients of valuated matroids. This connects the local structure of spaces of Lorentzian polynomials with the incidence geometry of tropical linear spaces. A central object in this connection is the moduli space of codimension-1 tropical linear subspaces of a given tropical linear space. In this talk, I will show some new structural results on this moduli space and their implications for Lorentzian polynomials.

Young tableaux arise in the enumerative geometry of linear series on curves in formulas for the Chow class and the holomorphic Euler characteristic of Brill--Noether varieties. I will discuss an intriguing tropical generalization of these two facts: the formulas for Chow class and Euler characteristic of Brill--Noether loci on a general curve occur in the first and last terms of the Ehrhart polynomial of the tropical Brill--Noether loci on a chain of loops. I will speculate on some generalizations and algebraic analogs of this calculation.

Chow rings and augmented Chow rings of matroids played important roles in the settlement of the Heron-Rota-Welsh conjecture and the Dowling-Wilson top-heavy conjecture. Their Hilbert series have been extensively studied since then. It was shown by Ferroni, Mathern, Steven, and Vecchi, and independently by Wang, that the Hilbert series of Chow rings of matroids are $\gamma$-positive using inductive arguement followed from the semismall decompositions of the Chow ring of matroids. However, they do not have an interpretation for the coefficients in the $\gamma$-expansion. Recently, Angarone, Nathanson, and Reiner further conjectured that Chow rings of matroids are equivariant $\gamma$-positive under the action of groups of matroid automorphisms. In this talk, I will give a proof of this conjecture without using semismall decomposition, showing that both Chow rings and augmented Chow rings of matroids are equivariant $\gamma$-positive. Moreover, we obtain explicit descriptions for the coefficients of the equivariant $\gamma$-expansions. Then we consider the special case of uniform matroids which extends Shareshian and Wachs Schur-$\gamma$-positivity of Frobenius characteristics of the cohomologies of the permutahedral and the stellahedral varieties.