Seminars Sorted by Series

During the 2026-27 academic year the School will have a special program on Conformally Symplectic Dynamics and Geometry. Michael Hutchings, University of California, Berkeley will be the Distinguished Visiting Professor.

The purpose of this special...

This will be a survey talk about recent progress on pointwise convergence problems for multiple ergodic averages along polynomial orbits and their relations with the Furstenberg-Bergelson-Leibman conjecture.

Given a topological dynamical system $(X,T)$ a bounded sequence $(a_n)$ and $f\in C(X)$ we are interested in the asymptotic behavior of $$\frac{1}{\sum_{n\leq N}|a_n|}\sum_{n\leq N}a_nf(T^nx)$$

The restriction conjecture, one of the most central problems in harmonic analysis, studies the Fourier transform of functions defined on curved surfaces; specifically, it claims that the level sets of such Fourier transforms are relatively small...

A number is called y-smooth if all of its prime factors are bounded above by y. The set of y-smooth numbers below x forms a sparse subset of the integers below x as soon as x is sufficiently large in terms of y. If f_1, …, f_r \in Z[x_1,…,x_s] is a...

A word on d letters is an element of the free group of rank d, say, with basis x_1,…,x_d. Given a word w=w(x_1,…,x_d) on d letters, for every group G, there is a word map w:G^d—> G given by substituting the x_i’s with elements of G. We say that a...

A famous conjecture of Littlewood states that the Fourier transform of every set of N integers has $l^1$ norm at least log(N), up to a constant multiplicative factor. This was proved independently by McGehee-Pigno-Smith and Konyagin in the 1980s...

The talk will consists of a long historical introduction to  the topic of deviation
of ergodic averages for locally Hamiltonian flows on compact surafces  as well as
some current results obtained in collaboration with Corinna Ulcigrai  and Minsung...

The celebrated product theorem says if A is a generating subset of a finite simple group of Lie type G, then |AAA| \gg \min \{ |A|^{1+c}, |G| \}. In this talk, I will show that a similar phenomenon appears in the continuous setting: If A is a subset...

A discrete subgroup of PSL(2,C) is called a Kleinian group. I will present  a criterion on  when a discrete faithful representation of a Kleinian group into PSL(2,C) is a conjugation, or equivalently  a criterion on when an equivariant embedding of...

If a set of integers is syndetic (finitely many translates cover the integers), must it contain two integers whose ratio is a square?  No one knows.  In the broader context of the disjointness between additive and multiplicative configurations and...

A conjecture of Erdős states that for every large enough prime q, every reduced residue class modulo q is the product of two primes less than q. I will discuss my on-going work with Kaisa Matomäki establishing among other things a ternary variant of...

The Bowen-Ruelle conjecture predicts that geodesic flows on negatively curved manifolds are exponentially mixing with respect to all their equilibrium states. In a breakthrough in '98, Dolgopyat pioneered a method rooted in the thermodynamic...

We discuss some recent progress on the model-theoretic problem of classifying the reducts of the complex field (with named parameters and up to interdefinability). The tools we use include Castle’s recent solution of the Restricted Trichotomy...

The Chowla conjecture from 1965 predicts that all autocorrelations of the Liouville function vanish. In fact, after an adaptation, the Chowla conjecture was expected to hold for all aperiodic multiplicative functions with values in the unit disc (cf...

Finding the smallest integer N=ES_d(n) such that in every configuration of N points in R^d in general position there exist n points in convex position is one of the most classical problems in extremal combinatorics, known as the Erdős-Szekeres...

Horospherical group actions on homogeneous spaces are famously known to be extremely rigid. In finite volume homogeneous spaces, it is a special case of Ratner’s theorems that all horospherical orbit closures are homogeneous. Rigidity further...

It is an open question as to whether the prime numbers contain the sum A+B of two infinite sets of natural numbers A, B (although results of this type are known assuming the Hardy-Littlewood prime tuples conjecture).  Using the Maynard sieve and the...

Incidence bound for points and spheres in higher dimensions generally becomes trivial in higher dimensions due to the existence of the Lenz example consisting of two orthogonal circles in ${\Bbb R}^4$, and the corresponding construction in higher...

The last decade has witnessed a revolution in the circle of problems concerned with proving sharp moment inequalities for exponential sums on tori. This has in turn led to a better understanding of pointwise estimates, but this topic remains...

We show that for every positive integer k there are positive constants C and c such that if A is a subset of {1, 2, ..., n} of size at least C n^{1/k}, then, for some d \leq k-1, the set of subset sums of A contains a homogeneous d-dimensional...

The Gowers uniformity k-norm on a finite abelian group measures the averages of complex functions on such groups over k-dimensional arithmetic cubes. The inverse question about these norms asks if a large norm implies correlation with a function of...

The Mackey-Zimmer representation theorem is a key structural result from ergodic theory: Every compact extension between ergodic measure-preserving systems can be written as a skew-product by a homogeneous space of a compact group. This is used, e.g...

Complex dynamics explores the evolution of points under iteration of functions of complex variables. In this talk I will introduce into the context of complex dynamics, a new approximation tool allowing us to construct new examples of entire...

Given $n\in\mathbb{N}$ and $\xi\in\mathbb{R}$, let $\tau(n;\xi)=\sum_{d|n}d^{i\xi}$. Hall and Tenenbaum asked in their book \textit{Divisors} what is the value of $\max_{\xi\in[1,2]} |\tau(n;\xi)|$ for a ``typical'' integer $n$. I will present work...

Erdős-style geometry is concerned with combinatorial questions about simple geometric objects, such as counting incidences between finite sets of points, lines, etc. These questions can be typically viewed as asking for the possible number of...

The goal of this talk is to present new results dealing with the asymptotic joint independence properties of commuting strongly mixing transformations along polynomials. These results form natural strongly mixing counterparts to various weakly and...

Link to Abstract

In 1996 Manjul Barghava introduced a notion of P-orderings for arbitrary sets S of a Dedekind domain, with respect to a prime ideal P, which defined associated invariants called P-sequences. He combined these invariants to define generalized...

In its dynamical formulation, the Furstenberg—Sárközy theorem states that for any invertible measure-preserving system $(X, \mu, T)$, any set $A \subseteq X$ with $\mu(A) > 0$, and any integer polynomial $P$ with $P(0) = 0$,
$$c(A) = \lim_{N-M \to...

I will discuss pointwise ergodic theory as it developed out of Bourgain's work in the 80s, leading up to my work with Mirek and Tao on bilinear ergodic averages.

Ruzsa asked whether there exist Fourier-uniform subsets of $\mathbb{Z}/N\mathbb{Z}$ with very few 4-term arithmetic progressions (4-AP). The standard pedagogical example of a Fourier uniform set with a "wrong" density of 4-APs actually has 4-AP...

This talk is based on a joint work with Steve Lester.

We review the Gauss circle problem, and Hardy's conjecture regarding the order of magnitude of the remainder term. It is attempted to rigorously formulate the folklore heuristics behind Hardy's...

Let SO(3,R) be the 3D-rotation group equipped with the real-manifold topology and the normalized Haar measure \mu. Confirming a conjecture by Breuillard and Green, we show that if A is an open subset of SO(3,R) with sufficiently small measure, then...

Link to Abstract

This is the organizational meeting for a learning seminar during the fall term on topics related to non-abelian p-adic Hodge theory. 

With every bounded prism Bhatt and Scholze associated a cohomology theory of formal p-adic schemes. The prismatic cohomology comes equipped with the Nygaard filtration and the Frobenius endomorphism. The Bhatt-Scholze construction has been advanced...

Multiplier ideals in characteristic zero and test ideals in positive characteristic are fundamental objects in the study of commutative algebra and birational geometry in equal characteristic.  We introduced a mixed characteristic version of the...

This talk will introduce background, achievements and challenges in the quest to find non-Archimedean versions of the celebrated Corlette-Simpson correspondence, which on Kähler manifolds relates representations of the fundamental group to certain...

I will discuss the following conjecture: an irreducible $\bar{Q}$$_{\ell}$-local system L on a smooth complex algebraic variety S arises in cohomology of a family of varieties over S if and only if L can be extended to an etale local system over...

In this talk, we introduce the analytic de Rham stack for rigid varieties over $Q_p$ (and more general analytic stacks). This object is an analytic incarnation of the (algebraic) de Rham stack of Simpson, and encodes a theory of analytic D-modules...

Cohomology of classifying space/stack of a group G is the home which resides all characteristic classes of G-bundles/torsors. In this talk, we will try to explain some results on Hodge/de Rham cohomology of BG where G is a $p$-power order...

Etale cohomology of $F_p$-local systems does not behave nicely on general smooth p-adic rigid-analytic spaces; e.g., the $F_p$-cohomology of the 1-dimensional closed unit ball is infinite. 

However, it turns out that the situation is much better if...

The notion of $p$-adic shtukas are introduced by Scholze in his Berkeley lectures on $p$-adic geometry. They are closely related to $p$-divisible groups when their ``legs" are bounded by some minuscule cocharacter. But compared to $p$-divisible...

In this talk, I will first describe how classical Dieudonne module of finite flat group schemes and $p$-divisible groups can be recovered from crystalline cohomology of classifying stacks. Then, I will explain how in mixed characteristics, using...

I will present a new theory of motivic cohomology for general (qcqs) schemes. It is related to non-connective algebraic K-theory via an Atiyah-Hirzebruch spectral sequence. In particular, it is non-$A^1$-invariant in general, but it recovers...

I will present two settings where $q$-De Rham and prismatic vector bundles can be described in terms of modules over an appropriate ring of $q$-twisted differential operators and also the relation with former results. 

This is a joint work with...