Let A be an abelian variety over a strictly henselian discretely valued field K. In his 1992 paper "Néron models and tame ramification", Edixhoven has constructed a filtration on the special fiber of the Néron model of A that measures the behaviour of the Néron model with respect to tamely ramified extensions of K. The filtration is indexed by rational numbers in [0,1], and if A is wildly ramified, it is an open problem whether the places where it jumps are always rational. I will explain how an interpretation of the filtration in terms of logarithmic geometry leads to explicit formulas for the jumps in the case where A is a Jacobian, which confirms in particular that they are rational. This is joint work with Dennis Eriksson and Lars Halvard Halle.

# Past Number Theory Seminar

Mirror symmetry is a duality from string theory that states that given a Calabi-Yau variety, there exists another Calabi-Yau variety so that various geometric and physical data are exchanged. The investigation of this mirror correspondence has its roots in enumerative geometry and hodge theory, but has been later interpreted by Kontsevich in a categorical setting. This exchange in data is very powerful, and has been shown to persist for zeta functions associated to Calabi-Yau varieties, although there is no rigorous statement for what arithmetic mirror symmetry would be. Instead of directly trying to state and prove arithmetic mirror symmetry, we will instead use mirror symmetry as an intuitional framework to obtain arithmetic results for special Calabi-Yau pencils in projective space from the Hodge theoretic viewpoint. If time permits, we will discuss work in progress in starting to find arithmetic implications of Kontsevich's Homological Mirror Symmetry.

In this talk on joint work with REBECCA BELLOVIN we discuss the “local ε-isomorphism” conjecture of Fukaya and Kato for (crystalline) families of G_{Q_p}-representations. This can be regarded as a local analogue of the global Iwasawa main conjecture for families, extending earlier work of Kato for rank one modules, of Benois and Berger for crystalline representations with respect to the cyclotomic extension as well as of Loeffler, Venjakob and Zerbes for crystalline representations with respect to abelian p-adic Lie extensions of Q_p. Nakamura has shown Kato’s - conjecture for (ϕ,\Gamma)-modules over the Robba ring, which means in particular only after inverting p, for rank one and trianguline families. The main ingredient of (the integrality part of) the proof consists of the construction of families of Wach modules generalizing work of Wach and Berger and following Kisin’s approach via a corresponding moduli space.

There are several conjectures in the literature suggesting that absolute Galois groups of fields tend to be "as free as possible," given their "almost-abelian" data.

This can be made precise in various ways, one of which is via the notion of "1-formality" arising in analogy with the concept in rational homotopy theory.

In this talk, I will discuss several examples which illustrate this phenomenon, as well as some surprising diophantine consequences.

This discussion will also include some recent joint work with Guillot, Mináč, Tân and Wittenberg, concerning the vanishing of mod-2 4-fold Massey products in the Galois cohomology of number fields.

I will discuss some recent work, joint with R. Maffucci, concerning random Laplace eigenfunctions on the torus T^3=R^3/Z^3. Studying various statistics of these 'random waves' we will be confronted with an arithmetic question about linear relations among integer points on spheres.

In this talk we will start by introducing the notion of Siegel-Jacobi modular form and explain its close relation to Siegel modular forms through the Fourier-Jacobi expansion. Then we will discuss how one can attach an L-function to an appropriate (i.e. eigenform) Siegel-Jacobi modular form due to Shintani, and report on joint work with Jolanta Marzec on analytic properties of this L-function, extending results of Arakawa and Murase.

We develop the asymptotic formulas for correlations

\[ \sum_{n\le x}f_1(P_1(n))f_2(P_2(n))\cdot \dots \cdot f_m(P_m(n))\]

where $f_1,\dots,f_m$ are bounded ``pretentious" multiplicative functions, under certain natural hypotheses. We then deduce several desirable consequences: first, we characterize all multiplicative functions $f:\mathbb{N}\to\{-1,+1\}$ with bounded partial sums. This answers a question of Erd{\"o}s from $1957$ in the form conjectured by Tao. Second, we show that if the average of the first divided difference of multiplicative function is zero, then either $f(n)=n^s$ for $\operatorname{Re}(s)<1$ or $|f(n)|$ is small on average. This settles an old conjecture of K\'atai. Third, we discuss applications to the study of sign patterns of $(f(n),f(n+1),f(n+2))$ and $(f(n),f(n+1),f(n+2),f(n+3))$ where $f:\mathbb{N}\to \{-1,1\}$ is a given multiplicative function. If time permits, we discuss multidimensional version of some of the results mentioned above.

The equidistribution theorem for rational points on expanding horospheres with fixed denominator in the space of d-dimensional Euclidean lattices has been derived in the work by M. Einsiedler, S. Mozes, N. Shah and U. Shapira. The proof of their theorem requires ergodic theoretic tools, including Ratner's measure classification theorem. In this talk I will present an alternative approach, based on harmonic analysis and Weil's bound for Kloosterman sums. In the case of d=3, unlike the ergodic-theoretic approach, this provides an explicit estimate on the rate of convergence. This is a joint work with Jens Marklof.

In 2000, Vojta solved the n-squares problem under the Bombieri-Lang conjecture, by explicitly finding all the curves of genus 0 or 1 on the surfaces related to this problem. The fundamental notion used by him is $\omega$-integrality of curves.

In this talk, I will show a generalization of Vojta's method to find all curves of low genus in some surfaces, with arithmetic applications.

I will also explain how to use $\omega$-integrality to obtain a bound of the height of a non-constant morphism from a curve to $\mathbb{P}^2$ in terms of the number of intersections (without multiplicities) of its image with a divisor of a particular kind.

This proves some new special cases of Vojta's conjecture for function fields.

I will revisit the theory of Hodge-Tate local systems in the light of the p-adic Simpson correspondence. This is a joint work with Michel Gros.