Seminar on Algebraic Dynamics

Korea Institute for Advanced Study

June 2020 - July 2020

Invited Speakers

Fei Hu (University of Waterloo)

Jia Jia (National University of Singapore)

Yohsuke Matsuzawa (Brown University)

Takahiro Shibata (National University of Singapore)

Shou Yoshikawa (The University of Tokyo)

Guolei Zhong (National University of Singapore)

Organizer

Sheng Meng (KIAS)

shengmeng@kias.re.kr

In this seminar, the speakers will talk about recent progress on algebraic dynamic, involving with height functions, orbits, rigidities, etc. The target audience will include, but not limited to, graduate students and non-experts.

Youtube: https://www.youtube.com/playlist?list=PLnQ8kPUvO6E1pLLOwsbUUlxxbqSDOgCs3

Schedule

Growth of local heights along orbits

Speaker: Yohsuke Matsuzawa

Time: 10 June 2020, 11:00-12:00 (Seoul)

Abstract

In 1993, Silverman proved that the coordinates of orbits on P^1 have asymptotically the same digits.

Behind this theorem, there is an estimate of growth of local height function on P^1 along the orbit.

I generalized the problem to higher dimensional dynamical systems on algebraic varieties involving local heights associated with closed subschemes.

I proved a generalization of Silverman's theorem, partially assuming Vojta's conjecture.

Dynamical degrees of self-maps on abelian varieties

Speaker: Fei Hu

Time: 17 June 2020, 11:00-12:00 (Seoul)

Abstract

Let $X$ be a smooth projective variety defined over an algebraically closed field of arbitrary characteristic, and $f\colon X \to X$ a surjective morphism. The $i$-th cohomological dynamical degree $\chi_i(f)$ of $f$ is defined as the spectral radius of the pullback $f^*$ on the \'etale cohomology group $H^i_{et}(X, \bQ_\ell)$ and the $k$-th numerical dynamical degree $\lambda_k(f)$ as the spectral radius of the pullback $f^*$ on the vector space $N^k(X)_\bR$ of real algebraic cycles of codimension $k$ modulo numerical equivalence. Truong conjectured that $\chi_{2k}(f) = \lambda_k(f)$ for any $1 \le k \le \dim X$. When the ground field is the complex number field, the equality follows from the positivity property inside the de Rham cohomology of the ambient complex manifold $X(\bC)$. We prove this conjecture in the case of abelian varieties. The proof relies on a new result on the eigenvalues of self-maps of abelian varieties in prime characteristic, which is of independent interest.

Density of points with maximal arithmetic degree

Speaker: Takahiro Shibata

Time: 24 June 2020, 11:00-12:00 (Seoul)

Abstract

Given an endomorphism on a projective variety over a number field, we can define the arithmetic degree at a rational point. It is known that the arithmetic degree at any point is less than or equal to the first dynamical degree. In this talk, we see that there are densely many rational points with maximal arithmetic degree. This is a joint work with Kaoru Sano.

Rigidity of rationally connected smooth projective varieties from dynamical viewpoints

Speaker: Guolei Zhong

Time: 1 July 2020, 11:00-12:00 (Seoul)

Abstract

In this talk, I will show that, a rationally connected smooth projective n-fold is n-th product of rational curves if and only if it admits a surjective endomorphism f with its pullback action on the Néron-Severi space having n distinct eigenvalues greater than 1. This is a joint work with Dr. Sheng Meng.

Surjective endomorphisms of normal projective surfaces

Speaker: Jia Jia

Time: 8 July 2020, 11:00-12:00 (Seoul)

Abstract

In this talk, we will give a structure theorem of endomorphisms of normal projective surfaces via equivariant minimal model program. Combining with some local dynamics and known results, we will give an application of the main theorem to Zariski dense orbit property in dimension two. This is a joint work with Dr Junyi Xie and Professor De-Qi Zhang.

Structure of varieties admitting an int-amplified endomorphism

Speaker: Shou Yoshikawa

Time: 15 July 2020, 11:00-12:00 (Seoul)

Abstract

In this talk, we will discuss the structure of varieties admitting a special endomorphism called polarized endomorphism or int-amplified endomorphism. Fujimoto and Nakayama classified smooth surfaces admitting a non-invertible endomorphism using equivariant contractions of (-1)-curves. This strategy also works in the higher dimensional case if we assume the variety has a special endomorphism proved by Meng and Zhang. Improving this strategy, we obtain Fano type fibrations replacing the variety into an étale cover.