Chow groups and $L$-derivatives of automorphic motives for unitary groups

TL;DR

This paper links the nonvanishing of central derivatives of automorphic L-functions to the nontriviality of certain Chow groups of unitary Shimura varieties, advancing the understanding of the Beilinson--Bloch conjecture and generalizing the Gross--Zagier formula.

Contribution

It proves a case of the Beilinson--Bloch conjecture for Chow groups and L-functions, constructs explicit elements via arithmetic theta lifting, and verifies a conjectural arithmetic inner product formula.

Findings

Nonvanishing of L'-values implies nontrivial Chow groups.

Explicit construction of Chow group elements using arithmetic theta lifting.

Height computations relate L'-values to geometric cycles.

Abstract

In this article, we study the Chow group of the motive associated to a tempered global $L$-packet $\pi$ of unitary groups of even rank with respect to a CM extension, whose global root number is $-1$. We show that, under some restrictions on the ramification of $\pi$, if the central derivative $L'(1/2,\pi)$ is nonvanishing, then the $\pi$-nearly isotypic localization of the Chow group of a certain unitary Shimura variety over its reflex field does not vanish. This proves part of the Beilinson--Bloch conjecture for Chow groups and $L$-functions, which generalizes the Birch and Swinnerton-Dyer conjecture. Moreover, assuming the modularity of Kudla's generating functions of special cycles, we explicitly construct elements in a certain $\pi$-nearly isotypic subspace of the Chow group by arithmetic theta lifting, and compute their heights in terms of the central derivative $L'(1/2,\pi)$ and local doubling zeta integrals. This confirms the conjectural arithmetic inner product formula proposed by one of us, which generalizes the Gross--Zagier formula to higher dimensional motives.