NTS ABSTRACTFall2022

Sep 08

Ziquan Yang

The Tate conjecture for h^{2, 0} = 1 varieties over finite fields

The past decade has witnessed a great advancement on the Tate conjecture for varieties with Hodge number h^{2, 0} = 1. Charles, Madapusi-Pera and Maulik completely settled the conjecture for K3 surfaces over finite fields, and Moonen proved the Mumford-Tate (and hence also Tate) conjecture for more or less arbitrary h^{2, 0} = 1 varieties in characteristic 0. In this talk, I will explain that the Tate conjecture is true for mod $p$ reductions of complex projective h^{2, 0} = 1 varieties when p is big enough, under a mild assumption on moduli. By refining this general result, we prove that in characteristic p at least 5 the BSD conjecture holds for a height 1 elliptic curve E over a function field of genus 1, as long as E is subject to the generic condition that all singular fibers in its minimal compacification are irreducible. We also prove the Tate conjecture over finite fields for a class of surfaces of general type and a class of Fano varieties. The overall philosphy is that the connection between the Tate conjecture over finite fields and the Lefschetz (1, 1)-theorem over the complex numbers is very robust for h^{2, 0} = 1 varieties, and works well beyond the hyperkahler world. This is based on joint work with Paul Hamacher and Xiaolei Zhao. Zoom ID: 93014934562 Password: The order of A9 (the alternating group of 9 elements)

Sep 15

Congling Qiu

Modularity of arithmetic special divisors for unitary Shimura varieties

We construct explicit generating series of arithmetic extensions of Kudla's special divisors on integral models of unitary Shimura varieties over CM fields with arbitrary split levels and prove that they are modular forms valued in the arithmetic Chow groups. This provides a partial solution to Kudla's modularity problem. The main ingredient in our construction is S. Zhang's theory of admissible arithmetic divisors. The main ingredient in the proof is an arithmetic mixed Siegel-Weil formula. Zoom ID: 93014934562 Password: The order of A9 (the alternating group of 9 elements)

Sep 22

Yousheng Shi

Special cycles on Shimura varieties and theta series

In this talk I will introduce special cycles on Shimura varieties and discuss how to use them to construct geometric and arithmetic theta series. Then I will briefly discuss the connection between these theta series and L functions. In particular I will introduce Kudla-Rapoport conjecture–one key ingredient to make the connection. Zoom ID: 93014934562 Password: The order of A9 (the alternating group of 9 elements)