关于Herman的正熵猜想
On Herman's Positive Entropy Conjecture
摘要：
我们发现，任何面积保持$C^r$ -同构的二维表面显示一个椭圆不动点可以$C^r$ -扰动到一个表现出混沌岛的度量熵是积极的，对于每个$1\le r\le \infty$。这证明了Herman的一个猜想，即圆盘的恒等映射可以被$C^\infty$ -扰动为具有正度量熵的保守双同态。这也意味着奇里科夫标准映射的大小参数值可以是$C^\infty$ -近似的保守的同构显示一个积极的度量熵（弱版本的西奈的积极度量熵猜想）。最后，这揭示了赫尔曼的问题上的密度的$C^r$ -保守的仿射显示一个积极的度量熵：我们显示存在一个稠密的集形成的保守仿射要么是弱稳定的（所以，从理论上讲，一致双曲）或显示一个混乱的岛屿的积极度量熵。
英文摘要：
We show that any area-preserving $C^r$-diffeomorphism of a two-dimensional surface displaying an elliptic fixed point can be $C^r$-perturbed to one exhibiting a chaotic island whose metric entropy is positive, for every $1\le r\le \infty$. This proves a conjecture of Herman stating that the identity map of the disk can be $C^\infty$-perturbed to a conservative diffeomorphism with positive metric entropy. This implies also that the Chirikov standard map for large and small parameter values can be $C^\infty$-approximated by a conservative diffeomorphisms displaying a positive metric entropy (a weak version of Sinai's positive metric entropy conjecture). Finally, this sheds light onto a Herman's question on the density of $C^r$-conservative diffeomorphisms displaying a positive metric entropy: we show the existence of a dense set formed by conservative diffeomorphism which either are weakly stable (so, conjecturally, uniformly hyperbolic) or display a chaotic island of positive metric entropy.
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