# Scientific

## A construction of Bowen-Margulis measure (Main talk)

In this talk we try to understand the Bowen-Margulis measure for geodesic flow on manifolds of (variable) negative curvature. In the first half-hour (pre-talk), I will discuss the necessary backgrounds from hyperbolic geometry and dynamics, and during the next hour (main talk), I will explain a construction due to Hamenstädt, which relates Bowen-Margulis measure to the Hausdorff measure with respect to a certain metric.

## A construction of Bowen-Margulis measure (Pre-Talk)

In this talk we try to understand the Bowen-Margulis measure for geodesic flow on manifolds of (variable) negative curvature. In the first half-hour (pre-talk), I will discuss the necessary backgrounds from hyperbolic geometry and dynamics, and during the next hour (main talk), I will explain a construction due to Hamenstädt, which relates Bowen-Margulis measure to the Hausdorff measure with respect to a certain metric.

## The value distribution of the Hurwitz zeta function with an irrational shift

The Hurwitz zeta function $\zeta(s, \alpha)$ is a shifted integer analogue of the Riemann zeta function which shares many of its properties, but is not an ”L-function” under any reasonable definition of the word. We will first review the basics of the value distribution of the Riemann zeta function in the critical strip (moments, Bohr–Jessen theory...) and then contrast it with the value distribution of the Hurwitz zeta function.

Our focus will be on shift parameters $\alpha / \in \mathbb{Q}$, i.e., algebraic irrational or transcendental. We will present a new result (joint with Winston Heap) on moments of these objects on the critical line.

## On the Quality of the ABC-Solutions

The quality of the triplet $(a,b,c)$, where $\gcd(a,b,c) = 1$, satisfying $a + b = c$ is defined as

$$

q(a,b,c) = \frac{\max\{\log |a|, \log |b|, \log |c|\}}{\log \mathrm{rad}(|abc|)},

$$

where $\mathrm{rad}(|abc|)$ is the product of distinct prime factors of $|abc|$. We call such a triplet an $ABC$-solution. The $ABC$-conjecture states that given $\epsilon > 0$ the number of the $ABC$-solutions $(a,b,c)$ with $q(a,b,c) \geq 1 + \epsilon$ is finite.

In the first part of this talk, under the $ABC$-conjecture, we explore the quality of certain families of the $ABC$-solutions formed by terms in Lucas and associated Lucas sequences. We also introduce, unconditionally, a new family of $ABC$-solutions that has quality $> 1$.

In the remaining of the talk, we prove a conjecture of Erd\"os on the solutions of the Brocard-Ramanujan equation

$$

n! + 1 = m^2

$$

by assuming an explicit version of the $ABC$-conjecture proposed by Baker.

## Theta-finite pro-Hermitian vector bundles from loop groups elements

In the finite-dimensional situation, Lie's third theorem provides a correspondence between Lie groups and Lie algebras. Going from the latter to the former is the more complicated construction, requiring a suitable representation, and taking exponentials of the endomorphisms induced by elements of the group.

As shown by Garland, this construction can be adapted for some Kac-Moody algebras, obtained as (central extensions of) loop algebras. The resulting group is called a loop group. One also obtains a relevant infinite-rank Chevalley lattice, endowed with a metric. Recent work by Bost and Charles provide a natural setting, that of pro-Hermitian vector bundles and theta invariants, in which to study these objects related to loop groups. More precisely, we will see in this talk how to define theta-finite pro-Hermitian vector bundles from elements in a loop group. Similar constructions are expected, in the future, to be useful to study loop Eisenstein series for number fields.

This is joint work with Manish M. Patnaik.

## Torsion points and concurrent lines on Del Pezzo surfaces of degree one

The blow up of the anticanonical base point on X, a del Pezzo surface of degree 1, gives rise to a rational elliptic surface E with only irreducible fibers. The sections of minimal height of E are in correspondence with the 240 exceptional curves on X.

A natural question arises when studying the configuration of those curves: If a point of X is contained in “many” exceptional curves, is it torsion on its fiber on E?

In 2005, Kuwata proved for del Pezzo surfaces of degree 2 (where there is 56 exceptional curves) that if “many” equals 4 or more, then yes. In a joint paper with Rosa Winter, we prove that for del Pezzo surfaces of degree 1, if “many” equals 9 or more, then yes. Moreover, we find counterexamples where a torsion point lies at the intersection of 7 exceptional curves.

## The question of q, a look at the interplay of number theory and ergodic theory in continued fractions

In the theory of continued fractions, the denominator of the truncated fraction (often denoted q) contains a great deal of information important in applications. However, q is a surprisingly complicated object from the point of view of ergodic theory. We will look at a few problems related to q and see how different techniques have overcome these difficulties, including modular properties (Moeckel, Fisher-Schmidt), renewal-type theorems (Sinai-Ulcigrai, Ustinov), and "nonstandard" arrangements of points (Avdeeva-Bykovskii).

## Sums of Fibonacci numbers close to a power of 2

The Fibonacci sequence \(F(n) : (n\geq 0) is the binary recurrence sequence defined by

$$

F(0) = F(1) = 1 \qquad \mbox{and} \\

F(n+2) = F(n+1) + F(n) \qquad \forall n \geq 0.

$$

There is a broad literature on the Diophantine equations involving the Fibonacci numbers. In this talk, we will study the Diophantine inequality

$$

\left\lvert F(n) + F(m) − 2a\right\rvert < 2a/2

$$

in positive integers n,m and a with $n \geq m$. The main tools used are lower bounds for linear forms in logarithms due to Matveev and Dujella-Petho version of the Baker-Davenport reduction method in Diophantine approximation.

## Quadratic Twists of Modular L-functions

The behavior of quadratic twists of modular L-functions at the critical point is related both to coefficients of half integer weight modular forms and data on elliptic curves. Here we describe a proof of an asymptotic for the second moment of this family of L-functions, previously available conditionally on the Generalized Riemann Hypothesis by the work of Soundararajan and Young. Our proof depends on deriving

an optimal large sieve type bound.

This event is part of the PIMS CRG Group on L-Functions in Analytic Number Theory. More details can be found on the webpage here: https://sites.google.com/view/crgl-functions/crg-weekly-seminar

## AI for Science; and the Implication for Mathematics

Modern machine learning has had remarkable success in all kinds of AI applications, and is also poised to change fundamentally the way we do research in traditional areas of science and engineering. In this talk, I will give an overview of some of the recent progress made in this exciting new direction and the theoretical and practical issues that I consider most important.