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This article is cited in 22 scientific papers (total in 22 papers)
Joint spectrum and the infinite dihedral group
Rostislav Grigorchukab, Rongwei Yangc a Department of Mathematics, Texas A&M University, College Station, TX 77843-3368, USA
b Steklov Mathematical Institute of Russian Academy of Sciences, ul. Gubkina 8, Moscow, 119991 Russia
c Department of Mathematics and Statistics, University at Albany, State University of New York, Albany, NY 12222, USA
Abstract:
For a tuple $A=(A_1,A_2,\dots,A_n)$ of elements in a unital Banach algebra $\mathcal B$, its projective joint spectrum $P(A)$ is the collection of $z\in\mathbb C^n$ such that the multiparameter pencil $A(z)=z_1A_1+z_2A_2+\dots+z_nA_n$ is not invertible. If $\mathcal B$ is the group $C^*$-algebra for a discrete group $G$ generated by $A_1,A_2,\dots,A_n$ with respect to a representation $\rho$, then $P(A)$ is an invariant of (weak) equivalence for $\rho $. This paper computes the joint spectrum of $R=(1,a,t)$ for the infinite dihedral group $D_\infty=\langle a,t\mid a^2=t^2=1\rangle$ with respect to the left regular representation $\lambda_{D_\infty}$, and gives an in-depth analysis on its properties. A formula for the Fuglede–Kadison determinant of the pencil $R(z)=z_0+z_1a+z_2t$ is obtained, and it is used to compute the first singular homology group of the joint resolvent set $P^\mathrm c(R)$. The joint spectrum gives new insight into some earlier studies on groups of intermediate growth, through which the corresponding joint spectrum of $(1,a,t)$ with respect to the Koopman representation $\rho$ (constructed through a self-similar action of $D_\infty$ on a binary tree) can be computed. It turns out that the joint spectra with respect to the two representations coincide. Interestingly, this fact leads to a self-similar realization of the group $C^*$-algebra $C^*(D_\infty)$. This self-similarity of $C^*(D_\infty)$ manifests itself in some dynamical properties of the joint spectrum.
Received: September 1, 2016
Citation:
Rostislav Grigorchuk, Rongwei Yang, “Joint spectrum and the infinite dihedral group”, Order and chaos in dynamical systems, Collected papers. On the occasion of the 125th anniversary of the birth of Academician Dmitry Victorovich Anosov, Trudy Mat. Inst. Steklova, 297, MAIK Nauka/Interperiodica, Moscow, 2017, 165–200; Proc. Steklov Inst. Math., 297 (2017), 145–178
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https://www.mathnet.ru/eng/tm3797https://doi.org/10.1134/S0371968517020091 https://www.mathnet.ru/eng/tm/v297/p165
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