3
$\begingroup$

We say that an invariant measure $\mu$ on some symbolic space $\Sigma$ has local product structure if there is a measurable function $\psi: \Sigma \rightarrow(0, \infty)$ such that the restriction is of the form $$ \mu_{|[I]}=\psi(\mu^{+} \times \mu^{-}),$$ where $\psi$ is continuous and positive, and $\mu^{+}$ and $\mu^{-}$ are the projections of $\mu_{|[I]}$ to the spaces of one-sided sequences indexed by positive and negative integers, respectively.

Let $T:\Sigma \to \Sigma$ be a full shift. Are all $T-$ invariant measures have the local product structure?if not, could you please give an example ?

Update: Let $f:M \to M$ be a $C^{1+\alpha}$ diffeomorphism. Is it true that all hyperbolic measures have local product structure?

$\endgroup$

1 Answer 1

4
$\begingroup$

No. Take $\mu$ to be a measure supported on a Sturmian shift corresponding to some irrational rotation $R_\alpha$. If $\mathcal F^+$ denotes the $\sigma$-algebra generated by the coordinates in $\mathbb Z_{\ge 0}$ and $\mathcal F^-$ denotes the $\sigma$-algebra generated by coordinates in $\mathbb Z_{<0}$, then conditional on $\mathcal F^+$, $\mu$ is supported on a single point (there is an almost everywhere one-one correspondence between negative and positive tails). This means $\mu$ is very far from a product of $\mu^-$ and $\mu^+$ (in which for each positive tail, all negative tails occur with conditional probability $\psi$).

$\endgroup$
4
  • $\begingroup$ Thanks for your answer. What about hyperbolic measures? Is it true that all hyperbolic measures have the local product structure ? $\endgroup$
    – Adam
    Commented Jun 29, 2021 at 20:51
  • $\begingroup$ What do you mean by a hyperbolic measure? $\endgroup$ Commented Jun 29, 2021 at 22:59
  • $\begingroup$ Lyaunov exponents of $f$ are non-zero a.e $\endgroup$
    – Adam
    Commented Jun 30, 2021 at 9:04
  • 1
    $\begingroup$ Are we still talking about the shift space? If so, the Lyapunov exponents are $\pm\log 2$ everywhere. $\endgroup$ Commented Jun 30, 2021 at 17:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .