Spectrum of weighted Birkhoff average

Let ${s_n}_{ninmathbb{N}}$ be a decreasing nonsummable sequence of positive reals. In this paper, we investigate the weighted Birkhoff average $frac{1}{S_n}sum_{k=0}^{n-1}s_kphi(T^kx)$ on aperiodic irreducible subshift of finite type $Sigma_{bf A}$ where $phi: Sigma_{bf A}mapsto mathbb{R}$ is a continuous potential. Firstly, we show the entropy spectrum of the weighed Birkhoff averages remains the same as that of the Birkhoff averages. Then we prove that the packing spectrum of the weighed Birkhoff averages equals to either that of the Birkhoff averages or the whole space.

Zero-dimensional and symbolic extensions of topological flows

A zero-dimensional (resp. symbolic) flow is a suspension flow over a zero-dimensional system (resp. a subshift). We show that any topological flow admits a principal extension by a zero-dimensional flow. Following [Bur19] we deduce that any topological flow admits an extension by a symbolic flow if and only if its time-$t$ map admits an extension by a subshift for any $t eq 0$. Moreover the existence of such an extension is preserved under orbit equivalence for regular topological flows, but this property does not hold more true for singular flows. Finally we investigate symbolic extensions for singular suspension flows. In particular, the suspension flow over the full shift on ${0,1}^{mathbb Z}$ with a roof function $f$ vanishing at the zero sequence $0^infty$ admits a principal symbolic extension or not depending on the smoothness of $f$ at $0^infty$.

Mean dimension of continuous cellular automata

We investigate the mean dimension of a cellular automaton (CA for short) with a compact non-discrete space of states. A formula for the mean dimension is established for (near) strongly permutative, permutative algebraic and unit one-dimensional automata. In higher dimensions, a CA permutative algebraic or having a spaceship has infinite mean dimension. However, building on Meyerovitchs example, we give an example of algebraic surjective cellular automaton with positive finite mean dimension.

Divergent coindex sequence for dynamical systems

When a finite group freely acts on a topological space, we can define its index and coindex. They roughly measure the size of the given action. We explore the interaction between this index theory and topological dynamics. Given a fixed-point free dynamical system, the set of $p$-periodic points admits a natural free action of $mathbb{Z}/pmathbb{Z}$ for each prime number $p$. We are interested in the growth of its index and coindex as $pto infty$. Our main result shows that there exists a fixed-point free dynamical system having the divergent coindex sequence. This solves a problem posed by [TTY20].

Finite mean dimesnion and marker property

In this paper, we develop the theory of $mathbb{Z}_p$-index which has been introduced by Tsukamoto, Tsutaya and Yoshinaga. As an application, we show that given any positive number, there exists a dynamical system with mean dimension equal to such number such that it does not have the marker property.

On variational principles for metric mean dimension

In this note, we show several variational principles for metric mean dimension. First we prove a variational principles in terms of Shapiras entropy related to finite open covers. Second we establish a variational principle in terms of Katoks entropy. Finally using these two variational principles we develop a variational principle in terms of Brin-Katok local entropy.

Embedding theorems for discrete dynamical systems and topological flows

In this paper, we investigate the embeddings for topological flows. We prove an embedding theorem for discrete topological system. Our results apply to suspension flows via constant function, and for this case we show an embedding theorem for suspension flows and give a new proof of Gutman-Jin embedding theorem.

On the multifractal spectrum of weighted Birkhoff averages

In this paper, we study the topological spectrum of weighted Birkhoff averages over aperiodic and irreducible subshifts of finite type. We show that for a uniformly continuous family of potentials, the spectrum is continuous and concave over its domain. In case of typical weights with respect to some ergodic quasi-Bernoulli measure, we determine the spectrum. Moreover, in case of full shift and under the assumption that the potentials depend only on the first coordinate, we show that our result is applicable for regular weights, like Mobius sequence.

A counter-example for polynomial version of Sarnaks conjecture

We construct the counter-example for polynomial version of Sarnaks conjecture for minimal systems, which assets that the Mobius function is linearly disjoint from subsequences along polynomials of deterministic sequences realized in minimal systems. Our example is in the class of Toeplitz systems, which are minimal.

On $p$-adic spectral measures

A Borel probability measure $mu$ on a locally compact group is called a spectral measure if there exists a subset of continuous group characters which forms an orthogonal basis of the Hilbert space $L^2(mu)$. In this paper, we characterize all spectral measures in the field $mathbb{Q}_p$ of $p$-adic numbers.