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Dynamical systems on measure spaces, invariant measures, ergodic averages, mixing properties.

4 votes
1 answer
270 views

A sufficient condition for an ergodic system to be weakly mixing

Let $\mathbf X := (X, \mathcal S, \mu, T)$ be an ergodic measure preserving system with finite measure such that for every increasing sequence $\{n_k\}$ of natural numbers with positive lower density, …
Nate River's user avatar
  • 6,321
0 votes
1 answer
211 views

Uniformity of convergence in the pointwise ergodic theorem

Definitions and some motivation: Let $X$ be a compact metric space, and $T$ a uniquely ergodic measure preserving transformation on $X$, with associated invariant ergodic probability measure $\mu$. As …
Nate River's user avatar
  • 6,321
3 votes
1 answer
333 views

Can every ergodic map be approximated by ergodic maps close to the identity?

Let $\mathbf X := (X, \mathcal S, \mu)$ be a probability space without atoms. We say two measure preserving transformations $T$ and $F$ on $\mathbf X$ are $\delta$-close, for $\delta > 0$, if $ \int_X …
Nate River's user avatar
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1 vote
1 answer
208 views

Robustness of ergodic dynamical systems

Let $\mathbf X := (X, \mathcal F, \mu)$ be a standard probability space. For an ergodic measure preserving transformation $T$, we define the ergodic robustness $\mathcal R(T)$ of $T$ as follows: For $ …
Nate River's user avatar
  • 6,321
3 votes
1 answer
147 views

Are $C^1$ vector fields generating an ergodic flow $C^0$ dense?

Note: This is a concrete case of the following question: Are almost all measure-preserving flows on compact manifolds ergodic? Let $M$ be a Riemannian manifold with its natural Riemannian measure, and …
Nate River's user avatar
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0 votes
1 answer
133 views

Entropy maximising ergodic transformation

Let $(\Omega, \mathcal F, \mu)$ be a standard probability space. Question: For each $f \in L^\infty (\Omega)$, does there exist an ergodic measure preserving transformation $T: \Omega \to \Omega$ such …
Nate River's user avatar
  • 6,321
3 votes
1 answer
237 views

Does an “almost mixing” transformation admit a non-null ergodic component?

Problem set up: Let $\mathbf X := (X, \mathcal A, \mu)$ be a standard probability space. We say that a measure preserving transformation $T$ on $\mathbf X$ is $\varepsilon$-almost mixing if for every …
Nate River's user avatar
  • 6,321
3 votes
1 answer
187 views

Does uniform recurrence imply uniform convergence of the Birkhoff sums?

Let $(X, T, \mathcal F, \mu)$ be an ergodic measure preserving system with finite measure. Suppose $T$ is uniformly recurrent, in the following sense: For every $A \in \mathcal F$, there exists an $M …
Nate River's user avatar
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2 votes
1 answer
141 views

Uniformly weak mixing transformations

Let $(X, T, \mathcal F, \mu)$ be a nonatomic standard probability space equipped with a measure preserving transformation $T$. We say $T$ is uniformly weak mixing if for every $\varepsilon > 0$, there …
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7 votes
1 answer
1k views

If the pointwise ergodic theorem holds along all subsequences with nonzero natural density, ...

Let $\mathbf X := (X, \mathcal S, \mu, T)$ be an ergodic measure preserving system with finite measure such that for every increasing sequence $\{n_k\}$ of natural numbers whose natural density exists …
Nate River's user avatar
  • 6,321
1 vote
1 answer
311 views

Alternate definitions of compact and weak mixing extensions

In Furstenberg's proof of the multiple recurrence theorem in ergodic theory, one makes use of the concept of compact and weak mixing extensions of a measure preserving system. The following definition …
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1 vote
1 answer
52 views

On the maximal difference between points in orbit

Let $(X, T, \mu)$ be an ergodic measure preserving system with finite measure, and $f \in L^{\infty} (X)$. Define the maximal orbit deviation function $D_f: X \to \mathbb R$ by $$D_f := \sup_{n, m \ge …
Nate River's user avatar
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4 votes
1 answer
241 views

Does an “almost weakly mixing” transformation admit a non-null ergodic component?

Problem set up: Let $\mathbf X := (X, \mathcal A, \mu)$ be a standard probability space. We say that a measure preserving transformation $T$ on $\mathbf X$ is $\varepsilon$-almost weakly mixing if for …
Nate River's user avatar
  • 6,321
1 vote
1 answer
180 views

Is a “uniformly minimal” dynamical system ergodic?

Let $X$ be a compact metric space, and $\mu$ a probability measure on $X$ with $\text{supp} \ \mu = X$. Suppose $T: X \to X$ is continuous, measure preserving and uniformly transitive in the sense tha …
Nate River's user avatar
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5 votes
1 answer
306 views

Is a random circle rotation weak mixing almost surely?

Consider the random circle rotation $x \to x + Z \text{ mod 1}$ on $([0, 1], \text{Lebesgue})$ where at each rotation, $Z$ is uniformly distributed on $[0, 1]$ and independent of previous rotations. I …
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