NTS ABSTRACTSpring2025

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Jan 30

L-values and the Mahler measures of polynomials

Xuejun Guo (Nanjing University)

When the zero locus of a tempered polynomial f(x,y) defines an elliptic curve E, the  value L(E,2) is related to the Mahler measure of  f(x,y). In this talk,  we will explore explicit identities that connect these L-values with Mahler measures for several families of polynomials.

Feb 6

The Geometry and Combinatorics of Matrix Points on Curves

Yifan Wei (UW-Madison)

The study of matrix points on curves was initiated by Yifeng Huang in his consideration of Cohen-Lenstra series, which captures the groupoid point-counts of the number of commuting matrices solutions to the defining equation of a curve. In our recent work, we incorporated ideas from geometric representation theory to study the rational cohomology ring of the space of matrix solutions. This new work refines previous results on point-counts, and leads to interesting directions in algebraic combinatorics.

Feb 13

A new proof of the arithmetic Siegel-Weil formula

Joey Yu Luo (UW-Madison)

The arithmetic Siegel-Weil formula establishes a profound connection between intersection numbers in Shimura varieties and the Fourier coefficients of central derivatives of Eisenstein series. This result was proven by C. Li and W. Zhang in 2021 using local methods. In this talk, I will present a new proof of the formula that uses the local-global compatibility and the modularity of generating series of special divisors.

Feb 20

(A)FL at infinity and generating series of arithmetic CM cycles

Tonghai Yang (UW-Madison)

In this talk, we propose a FL and AFL at the real place with a proof of FL (if time permits). We also define a generating series of arithmetic CM cycles indexed by integer and conjecture it to be modular. Finally, we explain the connection between the two. This is a preliminary report of my joint work with Andreas Mihatsch and Siddarth Sankaran.

Mar 13

Criteria for pseudorepresentations to arise from genuine representations

Jinyue Luo (UChicago)

In application to modularity, one often seeks for an R=T theorem, that is, the deformation ring R is isomorphic to a (localized) Hecke algebra T. However, sometimes only the framed deformation ring exists. With the framing variables, it is obviously larger than the Hecke algebra. Pseudorepresentations, which is a generalization of the notion of traces of representations, was invented to get around this issue. We will introduce the notion of pseudorepresentations and discuss the criteria for pseudo representations to arise from genuine representations. Next, we will introduce the algorithm used to explicitly compute usual deformation rings and pseudodeformation rings for finitely presented groups, which leads to the discovery of a counterexample.