The rigidity of pseudo-rotations on the two-torus and a question of Norton-Sullivan

TL;DR

This paper establishes rigidity results for conservative irrational pseudo-rotations on the two-torus under certain conditions, explores their centralizers, and constructs examples that answer a question of Norton and Sullivan negatively.

Contribution

It extends rigidity theory for pseudo-rotations, characterizes topological linearizability, and provides counterexamples in the smooth category.

Findings

Rigidity results for $C^{r}$ and H"older pseudo-rotations.

Description of the structure of conservative centralizers.

Construction of a smooth, nonlinearizable pseudo-rotation diffeomorphism.

Abstract

We show that under certain boundedness condition, a $C^{r}$ conservative irrational pseudo-rotations on $\mathbb{T}^2$ with a generic rotation vector is $C^{r-1}$-rigid. We also obtain $C^0$-rigidity for H\"older pseudo-rotations with similar properties. These provide a partial generalisation of the main results in [B. Bramham, Invent. Math. (2015), no. 2, 561-580; A. Avila, B. Fayad, P. Le Calvez, D. Xu and Z. Zhang, arXiv: 1509.06906v1]. We then use these results to study conservative irrational pseudo-rotations on $\mathbb{T}^2$ with a generic rotation vector that is semi-conjugate to a translation via a semi-conjugacy homotopic to the identity. We show that the conservative centralizers of any such diffeomorphism is isomorphic to a uncountable subgroup of $\mathbb{R}^2/\mathbb{Z}^2$. In connection with a question of Alec Norton and Dennis Sullivan, we describe the topologically linearizable maps within this class using the topology of the conservative centralizer group. In the minimal case, we obtain a precise characterization of topological linearizability for all totally irrational vectors. We also construct a $C^\infty$ conservative and minimal totally irrational pseudo-rotation diffeomorphism that is semi-conjugate to a translation, but is topologically nonlinearizable. This gives a negative answer to the question of Norton and Sullivan in the $C^{\infty}$ category.