Actions of Cremona groups on CAT(0) cube complexes

Cremona groups over finite fields, Neretin groups, and non-positively curved cube complexes

We show that plane Cremona groups over finite fields embed as dense subgroups into Neretin groups, i.e. groups of almost automorphisms of rooted trees. We also show that if the finite base field has even characteristic and contains at least 4 elements, then the permutations induced by birational transformations on rational points of regular projective surfaces are even. In a second part, we construct explicit locally compact CAT(0) cube complexes, on which Neretin groups act properly. This allows us to recover in a unified way various results on Neretin groups such as that they are of type $F_…

关于高阶格的立方体和克雷莫纳刚性

On cube and Cremona rigidity for higher-rank lattices

研究实秩至少为2的半单李群中不可约格在CAT(0)立方体复形上的作用，通过证明上同调消失结果及利用超刚性等方法，得出相关作用可正则性的结论，绕过对FW性质的直接使用。

从中位数几何视角看Cremona群的综述

Survey on Cremona groups from a median geometric point of view

本文基于2023年Riverside研讨会讲义，介绍Cremona群在中位数图上作用的最新构造，旨在同时服务于几何群论学家和代数几何学家。

Categorical dimension of birational automorphisms and filtrations of Cremona groups

Using a filtration on the Grothendieck ring of triangulated categories, we define the categorical dimension of a birational map between smooth projective varieties. We show that birational automorphisms of bounded categorical dimension form subgroups, which provide a nontrivial filtration of the Cremona group. We discuss some geometrical aspect and some explicit example. In the case of threefolds, we can moreover recover the genus of a birational automorphism, and the filtration defined by Frumkin.

The action of the Cremona group on the non-commutative ring

The Cremona group acts on the field of two independent commutative variables over complex numbers. We provide a non-commutative ring that is an analog of non-commutative field of two independent variables and prove that the Cremona group embeds in the group of outer automorphisms of this ring. First proof of this result is technical, the second one is conceptual and gives a way to obtain non-commutative rings from the bounded derived categories of coherent sheaves.

Characterization of affine surfaces with a torus action by their automorphism groups

In this paper we prove that if two normal affine surfaces $S$ and $S'$ have isomorphic automorphism groups, then every connected algebraic group acting regularly and faithfully on $S$ acts also regularly and faithfully on $S'$. Moreover, if $S$ is non-toric, we show that the dynamical type of a 1-torus action is preserved in presence of an additive group action. We also show that complex affine toric surfaces are determined by the abstract group structure of their regular automorphism groups in the category of complex normal affine surfaces using properties of the Cremona group. As a generaliz…