arXiv subjects

Hiroki Matui

Publications and source records attributed to Hiroki Matui.

At least 19 recordsLinked to original sources

arXiv2026

HK and GL

We study the HK conjecture and the gap-labelling problem for transformation groupoids associated with free actions of poly-$\Z$ groups on Cantor sets. The main tool is a comparison of the long exact sequences in groupoid homology and cohomology with the Pimsner--Voiculescu exact sequence for crossed products by $\Z$. In addition to the canonical homology comparison maps $\mu_0$ and $\mu_1$, we introduce cohomology comparison maps associated with suitable $K$-theory classes of the acting group. Together with Poincar\'e duality, these maps detect the higher homology terms occurring in the HK conjecture. We apply this method to free actions of poly-$\Z$ groups of small Hirsch length. For actions of $\Z$, $\Z^2$, and the Klein bottle group, we recover HK and gap-labelling. For several classes of groups of Hirsch length three and four, we either prove HK or obtain explicit exact sequences describing the $K$-groups in terms of groupoid homology and cohomology. For gap-labelling, we combine the de la Harpe--Skandalis determinant, the trace formula for the Pimsner--Voiculescu boundary map, and transposition decompositions in topological full groups. This gives gap-labelling up to a factor of two for all free actions of poly-$\Z$ groups of Hirsch length three and for certain groups of Hirsch length four, including $\Z^4$. We also recover gap-labelling for $\Z^3$-actions and prove gap-labelling up to a factor of two for $\Z^5$-actions by using cohomology comparison maps for mapping tori.

math.OA↗

arXiv2026

Topological entropy in continuous orbit equivalence of one-sided topological Markov shifts

In this paper, we prove that the continuous orbit equivalence class of a one-sided topological Markov shift contains a one-sided topological Markov shift whose topological entropy is greater than an arbitrary prescribed positive real number, and also contains a one-sided topological Markov shift whose topological entropy is less than an arbitrary prescribed positive real number.

math.DS↗

arXiv2024

Classifying Stein's groups

In this paper, we provide a comprehensive classification of Stein's groups, which generalize the well-known Higman-Thompson groups. Stein's groups are defined as groups of piecewise linear bijections of an interval with finitely many breakpoints and slopes belonging to specified additive and multiplicative subgroups of the real numbers. Our main result establishes a classification theorem for these groups under the assumptions that the slope group is finitely generated and the additive group has rank at least 2. We achieve this by interpreting Stein's groups as topological full groups of ample groupoids. A central concept in our analysis is the notion of $H^1$-rigidity in the cohomology of groupoids. In the case where the rank of the additive group is 1, we adopt a different approach using attracting elements to impose strong constraints on the classification.

math.DS↗

arXiv2024

Cup and cap products for cohomology and homology groups of ample groupoids

This paper explores the cup and cap products within the cohomology and homology groups of ample groupoids, focusing on their applications and fundamental properties. Ample groupoids, which are \'etale groupoids with a totally disconnected unit space, play a crucial role in the study of topological dynamical systems and operator algebras. We introduce the cup product, which defines a bilinear map on cohomology classes, providing a graded ring structure, and the cap product, which defines a bilinear map relating homology and cohomology. The paper aims to make these concepts accessible to a broader mathematical audience, offering clear definitions and detailed explanations. We also demonstrate an application of the cap product in the analysis of automorphisms of groupoid $C^*$-algebras. Specifically, we show how it helps determine the asymptotic innerness of automorphisms. Our results include the first explicit computations of cup products in the cohomology of tiling spaces, which may pave the way for new research in this area.

math.OA↗

arXiv2021

Long exact sequences of homology groups of \'etale groupoids

When a pair of \'etale groupoids $\mathcal{G}$ and $\mathcal{G}'$ on totally disconnected spaces are related in some way, we discuss the difference of their homology groups. More specifically, we treat two basic situations. In the subgroupoid situation, $\mathcal{G}'$ is assumed to be an open regular subgroupoid of $\mathcal{G}$. In the factor groupoid situation, we assume that $\mathcal{G}'$ is a quotient of $\mathcal{G}$ and the factor map $\mathcal{G}\to\mathcal{G}'$ is proper and regular. For each, we show that there exists a long exact sequence of homology groups. We present examples which arise from SFT groupoids and hyperplane groupoids.

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arXiv2019

Poly-$\mathbb{Z}$ group actions on Kirchberg algebras II

This is the second part of our serial work on the classification of poly-$\mathbb{Z}$ group actions on Kirchberg algebras. Based on technical results obtained in our previous work, we completely reduce the problem to the classification of continuous fields of Kirchberg algebras over the classifying spaces. As an application, we determine the number of cocycle conjugacy classes of outer $\mathbb{Z}^n$-actions on the Cuntz algebras.

math.OA↗

arXiv2018

A weak homotopy equivalence type result related to Kirchberg algebras

We obtain a weak homotopy equivalence type result between two topological groups associated with a Kirchberg algebra: the unitary group of the continuous asymptotic centralizer and the loop group of the automorphism group of the stabilization. This result plays a crucial role in our subsequent work on the classification of poly-$\mathbb{Z}$ group actions on Kirchberg algebras. As a special case, we show that the $K$-groups of the continuous asymptotic centralizer are isomorphic to the $KK$-groups of the Kirchberg algebra.

math.OA↗

arXiv2018

Poly-$\mathbb{Z}$ group actions on Kirchberg algebras I

Toward the complete classification of poly-$\mathbb{Z}$ group actions on Kirchberg algebras, we prove several fundamental theorems that are used in the classification. In addition, as an application of them, we classify outer actions of poly-$\mathbb{Z}$ groups of Hirsch length not greater than three on unital Kirchberg algebras up to $KK$-trivial cocycle conjugacy.

math.OA↗

arXiv2016

Topological full groups of etale groupoids

This is a survey of the recent development of the study of topological full groups of etale groupoids on the Cantor set. Etale groupoids arise from dynamical systems, e.g. actions of countable discrete groups, equivalence relations. Minimal Z-actions, minimal Z^N-actions and one-sided shifts of finite type are basic examples. We are interested in algebraic, geometric and analytic properties of topological full groups. More concretely, we discuss simplicity of commutator subgroups, abelianization, finite generation, cohomological finiteness properties, amenability, the Haagerup property, and so on. Homology groups of etale groupoids, groupoid C*-algebras and their K-groups are also investigated.

math.OA↗

arXiv2015

Etale groupoids arising from products of shifts of finite type

Two conjectures about homology groups, K-groups and topological full groups of minimal etale groupoids on Cantor sets are formulated. We verify these conjectures for many examples of etale groupoids including products of etale groupoids arising from one-sided shifts of finite type. Furthermore, we completely determine when these product groupoids are mutually isomorphic. Also, the abelianization of their topological full groups are computed. They are viewed as generalizations of the higher dimensional Thompson groups.

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arXiv2014

Universal properties of group actions on locally compact spaces

We study universal properties of locally compact G-spaces for countable infinite groups G. In particular we consider open invariant subsets of the β-compactification of G (which is a G-space in a natural way), and their minimal closed invariant subspaces. These are locally compact free G-spaces, and the latter are also minimal. We examine the properies of these G-spaces with emphasis on their universal properties. As an example of our resuts, we use combinatorial methods to show that each countable infinite group admits a free minimal action on the locally compact non-compact Cantor set.

math.GR↗

arXiv2014

Full groups of Cuntz-Krieger algebras and Higman-Thompson groups

In this paper, we will study presentations of the continuous full group $\Gamma_A$ of a one-sided topological Markov shift $(X_A,\sigma_A)$ for an irreducible matrix $A$ with entries in $\{0,1\}$ as a generalization of Higman-Thompson groups $V_N, 1<N \in {\mathbb{N}}$. We will show that the group $\Gamma_A$ can be represented as a group $\Gamma_A^{\operatorname{tab}}$ of matrices, called $A$-adic tables, with entries in admissible words of the shift space $X_A$, and a group $\Gamma_A^{\operatorname{PL}}$ of right continuous piecewise linear functions, called $A$-adic PL functions, on $[0,1]$ with finite singularities.

math.OA↗

arXiv2014

Continuous orbit equivalence of topological Markov shifts and dynamical zeta functions

For continuously orbit equivalent one-sided topological Markov shifts $(X_A,\sigma_A)$ and $(X_B,\sigma_B)$, their eventually periodic points and cocycle functions are studied. As a result we directly construct an isomorphism between their ordered cohomology groups $(\bar{H}^A, \bar{H}^A_+)$ and $(\bar{H}^B, \bar{H}^B_+)$. We also show that the cocycle functions for the continuous orbit equivalences give rise to positive elements of the ordered cohomology, so that the the zeta functions of continuously orbit equivalent topological Markov shifts are related. The set of Borel measures is shown to be invariant under continuous orbit equivalence of one-sided topological Markov shifts.

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arXiv2013

Decomposition rank of UHF-absorbing C*-algebras

Let A be a unital separable simple C*-algebra with a unique tracial state. We prove that if A is nuclear and quasidiagonal, then A tensored with the universal UHF-algebra has decomposition rank at most one. Then it is proved that A is nuclear, quasidiagonal and has strict comparison if and only if A has finite decomposition rank. For such A, we also give a direct proof that A tensored with a UHF-algebra has tracial rank zero. Applying this characterization, we obtain a counter-example to the Powers-Sakai conjecture.

math.OA↗

arXiv2013

Continuous orbit equivalence of topological Markov shifts and Cuntz-Krieger algebras

Let A,B be square irreducible matrices with entries in {0,1}. We will show that if the one-sided topological Markov shifts (X_A,\sigma_A) and (X_B,\sigma_B) are continuously orbit equivalent, then the two-sided topological Markov shifts (\bar X_A,\bar\sigma_A) and (\bar X_B,\bar\sigma_B) are flow equivalent, and hence det(id-A)=det(id-B). As a result, the one-sided topological Markov shifts (X_A,\sigma_A) and (X_B,\sigma_B) are continuously orbit equivalent if and only if the Cuntz-Krieger algebras O_A and O_B are isomorphic and det(id-A)=det(id-B).

math.OA↗

arXiv2013

Topological full groups of $C^*$-algebras arising from $\beta$-expansions

We will introduce a family $\Gamma_\beta, 1 < \beta \in {\mathbb{R}}$ of infinite non-amenable discrete groups as an interpolation of the Higman-Thompson groups $V_n, 1 < n \in {\mathbb{N}}$ by using the topological full groups of the groupoids defined by $\beta$-expansions of real numbers. They are regarded as full groups of certain interpolated Cuntz algebras. The groups $\Gamma_\beta, 1 < \beta \in {\mathbb{R}}$ are realized as groups of piecewise linear functions on $[0,1]$ if the $\beta$-expansion of $1$ is finite or ultimately periodic. We also classify the groups $\Gamma_\beta, 1 < \beta \in {\mathbb{R}}$ by the number theoretical property of $\beta$.

math.OA↗

arXiv2013

Topological full groups of one-sided shifts of finite type

We explore the topological full group [[G]] of an essentially principal etale groupoid G on a Cantor set. When G is minimal, we show that [[G]] (and its certain normal subgroup) is a complete invariant for the isomorphism class of the etale groupoid G. Furthermore, when G is either almost finite or purely infinite, the commutator subgroup D([[G]]) is shown to be simple. The etale groupoid G arising from a one-sided irreducible shift of finite type is a typical example of a purely infinite minimal groupoid. For such G, [[G]] is thought of as a generalization of the Higman-Thompson group. We prove that [[G]] is of type F_\infty, and so in particular it is finitely presented. This gives us a new infinite family of finitely presented infinite simple groups. Also, the abelianization of [[G]] is calculated and described in terms of the homology groups of G.

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arXiv2012

Z-stability of crossed products by strongly outer actions II

We consider a crossed product of a unital simple separable nuclear stably finite Z-stable C*-algebra A by a strongly outer cocycle action of a discrete countable amenable group \Gamma. Under the assumption that A has finitely many extremal tracial states and \Gamma is elementary amenable, we show that the twisted crossed product C*-algebra is Z-stable. As an application, we also prove that all strongly outer cocycle actions of the Klein bottle group on Z are cocycle conjugate to each other. This is the first classification result for actions of non-abelian infinite groups on stably finite C*-algebras.

math.OA↗