Banach October 2021

banach@mathdept.okstate.edu

1 participants
2 discussions

Colloquium by Thomas Schlumprecht on Oct 21 at UIUC
by Sari, Bunyamin 19 Oct '21

19 Oct '21

Dear all, There is a Math Colloquium talk at University of Illinois Urbana-Champagne on Thursday October 21 by Thomas Schlumprecht. The info is below. Please make sure to use the zoom link below and also note that it is on a different date and time than our usual webinars. Best, Bunyamin Join Zoom Meeting https://illinois.zoom.us/j/86232022920?pwd=SVg2UGhTSkN6TkxTdFhYZ1psNzAzQT09<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fillinois.…> Meeting ID: 862 3202 2920 Password: 999491 Speaker: Thomas Schlumprecht (Texas A&M) Title: Lamplighter metric spaces and their embeddings into $L_1$ Abstract: Understanding how a group or a graph, viewed as a geometric object, can be faithfully embedded into certain Banach spaces is a fundamental topic with applications to geometric group theory and theoretical computer science. In this joint work with Florent Baudier, Pavlos Motakis and Andras Zsak we observe that embeddings into random metrics can be fruitfully used to study the $L_1$-embeddability of lamplighter graphs or groups, and more generally lamplighter metric spaces. Once this connection has been established, several new upper bound estimates on the $L_1$-distortion of lamplighter metrics follow from known related estimates about stochastic embeddings into dominating tree-metrics. For instance, every lamplighter metric on a $n$-point metric space embeds bi-Lipschitzly into $L_1$ with distortion $O(\log n)$. In particular, for every finite group $G$ the lamplighter group $H = \mathbb{Z}_2\wr G$ bi-Lipschitzly embeds into $L_1$ with distortion $O(\log\log|H|)$. In the case where the ground space in the lamplighter construction is a graph with some topological restrictions, better distortion estimates can be achieved. Finally, we discuss how a coarse embedding into $L_1$ of the lamplighter group over the $d$-dimensional infinite lattice $\mathbb Z^d$ can be constructed from bi-Lipschitz embeddings of the lamplighter graphs over finite $d$-dimensional grids, and we include a remark on Lipschitz free spaces over finite metric spaces.

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Banach spaces webinar on Oct 15 by Pavlos Motakis
by Sari, Bunyamin 13 Oct '21

13 Oct '21

Hello, The next Banach spaces webinar is on Friday October 15 9AM Central time. Please join us at https://unt.zoom.us/j/83807914306 Title: Separable spaces of continuous functions as Calkin algebras Speaker: Pavlos Motakis, York University Abstract. The Calkin algebra $\mathcal{C}al(X)$ of a Banach space $X$ is the quotient algebra of all bounded linear operators $\mathcal{L}(X)$ on $X$ over the ideal of all compact ones $\mathcal{K}(X)$. A question that has gathered attention in recent years is what unital Banach algebras admit representations as Calkin algebras. There is a strong connection between quotients algebras of $\mathcal{L}(X)$ and the tight control of the operators on $X$ modulo a small ideal. We discuss a new contribution to this topic, namely that for every compact metric space $K$ there exists a Banach space $X$ so that $\mathcal{C}al(X)$ coincides isometrically with $C(K)$ as a Banach algebra. For more information about the past and future talks, and videos please visit the webinar website http://www.math.unt.edu/~bunyamin/banach Thank you, and best regards, Bunyamin Sari

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Banach October 2021