Abstracts

Shrenik Shah (Columbia U)
Class number formulae for some Shimura varieties of low dimension
The class number formula connects the residue of the Dedekind zeta function at s=1 to the regulator, which measures the covolume of the lattice generated by logarithms of units. Beilinson defined a generalized regulator morphism and conjectural class number formula in the "motivic" setting. His formula provides arithmetic meaning to the orders of "trivial" zeroes of Lfunctions at integer points as well as the value of the first nonzero derivative at these points.
We study this conjecture for the middle degree cohomology of the Shimura varieties associated to unitary groups of signature (2,1) and (2,2) over Q. We construct explicit "BeilinsonFlach elements" in the motivic cohomology of these varieties and compute their regulator. This is joint work with Aaron Pollack.

Nicole Looper (Northwestern U)
A lower bound on the canonical height for polynomials
The canonical height associated to a rational function defined over a number field measures arithmetic information about the forward orbits of points under that function. Silverman conjectured that given any number field K and degree d at least 2, there is a uniform lower bound on the canonical heights associated to degree d rational functions defined over K, evaluated at points of K having infinite forward orbit. I will discuss a proof of such a lower bound across large families of polynomials. I will also discuss related questions, both in the setting of elliptic curves and that of dynamical systems.

Liang Xiao (U Connecticut)
Cycles on the special fiber of some Shimura varieties and Tate conjecture
We describe the irreducible components of the basic locus of Shimura varieties of Hodge type at a place with good reduction, when the basic locus is of middle dimension. Under certain genericity condition, we show that they generate the Tate classes of the special fiber of the Shimura varieties. This is a joint work with Xinwen Zhu.

Lue Pan (Princeton U)
Fontaine–Mazur conjecture in the residually reducible case
We prove the modularity of some twodimensional residually reducible padic Galois representations over Q under certain hypothesis on the residual representation at p. To do this, we generalize Emerton's localglobal compatibility and devise a patching argument for completed homology in this setting.

Lucia Mocz (Princeton U)
A new Northcott property for Faltings height
The Faltings height is a useful invariant for addressing questions in arithmetic geometry. In his celebrated proof of the Mordell and Shafarevich conjectures, Faltings shows the Faltings height satisfies a certain Northcott property, which allows him to deduce his finiteness statements. In this work we prove a new Northcott property for the Faltings height. Namely we show, assuming the Colmez Conjecture and the Artin Conjecture, that there are finitely many CM abelian varieties of a fixed dimension which have bounded Faltings height. The technique developed uses new tools from integral padic Hodge theory to study the variation of Faltings height within an isogeny class of CM abelian varieties. In special cases, we are able to use these techniques to moreover develop new Colmeztype formulas for the Faltings height.

Daniel Kriz (Princeton U)
A new padic MaassShimura operator and supersingular RankinSelberg padic Lfunctions
We introduce a new padic MaassShimura operator acting on a space of "generalized padic modular forms" (extending Katz's notion of padic modular forms) defined on the padic (preperfectoid) universal cover of Shimura curves. Using this operator, we construct new padic Lfunctions in the style of Katz, BertoliniDarmonPrasanna and LiuZhangZhang for RankinSelberg families over imaginary quadratic fields K in the case where p is inert or ramified in K. We also establish new padic Waldspurger formulas, relating padic logarithms of elliptic units and Heegner points to special values of these padic Lfunctions.

Jingren Chi (U Chicago)
Geometry of generalized affine Springer fibers
This talk is about certain generalization of affine Springer fibers that arises naturally in the study of orbital integrals of spherical Hecke functions on a padic group. We compare basic geometric properties of these generalized affine Springer fibers with their classical Lie algebra analogue. In particular, we will formulate a conjecture relating the number of irreducible components of such varieties to certain weight multiplicities defined by the Langlands dual group and discuss known cases of this conjecture.

Isabel Leal (U Chicago)
Generalized HasseHerbrand functions
The classical HasseHerbrand function is an important object in ramification theory, related to higher ramification groups. In this talk, I will discuss generalizations of the HasseHerbrand function and go over some of their properties. These generalized HasseHerbrand functions are defined for extensions L/K of complete discrete valuation fields where the residue field k of K is perfect of characteristic p>0 but the residue field l of L is possibly imperfect.

Ari Schnidman (Boston C)
A higher order GrossKohnenZagier formula
I'll present a formula relating the intersection of two different HeegnerDrinfeld cycles to the rth derivative of an automorphic Lfunction. This is a "higherorder" generalization of the GrossKohnenZagier formula, in the function field setting, and is inspired by recent work of Yun and W. Zhang. Our formula gives strong evidence that all HeegnerDrinfeld cycles are colinear in cohomology. This is joint work with Ben Howard.

Anthony VárillyAlvarado (Rice U)
Vojta's conjecture and uniform boundedness of fulllevel structures on abelian varieties over number fields
In 1977, Mazur proved that the torsion subgroup of an elliptic curve over Q is, up to isomorphism, one of only 15 groups. Before Merel gave a qualitative generalization of this result to arbitrary number fields, it was known that variants of the abc conjecture would imply uniform boundedness of torsion on elliptic curves over number fields of bounded degree. In this talk, I will explain how, using Vojta’s conjecture as a higherdimensional generalization of the abc conjecture, one can deduce similar uniform boundedness statements for fulllevel structures on abelian varieties of fixed dimension over number fields. This is joint work with Dan Abramovich and Keerthi MadapusiPera.

KaiWen Lan (U Minnesota)
Nearby cycles of automorphic étale sheaves
I will explain that, in most cases where integral models are available in the literature, the automorphic étale cohomology of a (possibly noncompact) Shimura variety in characteristic zero is canonically isomorphic to the cohomology of the associated (ladic) nearby cycles in positive characteristics. If time permits, I will also talk about some applications or related results. (This is joint work with Stroh.)

Charlotte Chan (U Michigan)
Periods identities of CM forms on quaternion algebras
A few decades ago, Waldspurger proved a groundbreaking identity between the central value of an Lfunction and the norm of a torus period. Combining this with the JacquetLanglands correspondence gives a relationship between the norm of torus periods arising from different quaternion algebras for automorphic forms attached to Hecke characters. In this talk, we will give a direct proof of the identity of the torus periods themselves.

Jayce Getz (Duke U)
Summation formulae for triples of quadratic forms
Braverman and Kazhdan have conjectured the existence of summation formulae that are essentially equivalent to the analytic continuation and functional equation of Langlands Lfunctions in great generality. Motivated by their conjectures and related conjectures of L. Lafforgue, Ngo, and Sakellaridis, Baiying Liu and I have proven a summation formula analogous to the Poisson summation formula for the subscheme cut out of three quadratic spaces (V_i,Q_i) of even dimension by the equation Q_1(V_1)=Q_2(V_2)=Q_3(V_3). I will sketch the proof of this formula.
