Matthew Wiersma

activity

20112025

most citedC*-norms for tensor products of discrete group C*-algebras

11 citations · 35 across the 11 of their papers we have counts for

collaborators

18 papers

math.FA2025

On operator Connes-amenability of the Fourier-Stieltjes algebra

Volker Runde, Nico Spronk, Matthew Wiersma

Runde and Spronk showed in 2004 that there are non-amenable groups $G$ , including $F_{2}$ , {whose Fourier-Stieltjes algebra, $B (G)$ ,} is operator Connes-amenable. This result…

math.DS2024

Entropies and Poisson boundaries of random walks on groups with rapid decay

Benjamin Anderson-Sackaney, Tim de Laat, Ebrahim Samei +1

Let $G$ be a countable group and $μ$ a probability measure on $G$ . We build a new framework to compute asymptotic quantities associated with the $μ$ -random walk on $G$ , using metho…

math.OA2023

New tensor products of C-algebras and characterization of type I C-algebras as rigidly symmetric C*-algebras

Hun Hee Lee, Ebrahim Samei, Matthew Wiersma

We construct several new classes of bifunctors $(A, B) \mapsto A \otimes_{α} B$ , where $A \otimes_{α} B$ is a cross norm completion of $A ⊙ B$ for each pair of C*-algebras $A$ and $B$ . F…

math.OA2022

Traces on locally compact groups

Brian Forrest, Nico Spronk, Matthew Wiersma

We conduct a systematic study of traces on locally compact groups, in particular traces on their universal and reduced C*-algebras. We introduce the trace kernel, and examine its r…

math.OA2020★ 1 cited

Cohomological obstructions to lifting properties for full group C $^{*}$ -algebras

Adrian Ioana, Pieter Spaas, Matthew Wiersma

We develop a new method, based on non-vanishing of second cohomology groups, for proving the failure of lifting properties for full C $^{*}$ -algebras of countable groups with (relativ…

math.OA2018★ 1 cited

Exotic C*-algebras of geometric groups

Ebrahim Samei, Matthew Wiersma

We consider a new class of potentially exotic group C*-algebras $C_{P F_{p}^{*}}^{*} (G)$ for a locally compact group $G$ , and its connection with the class of potentially exotic group C*-…

math.FA2018

Quasi-Hermitian locally compact groups are amenable

Ebrahim Samei, Matthew Wiersma

A locally compact group $G$ is called Hermitian if the spectrum $Sp_{L^{1} (G)} (f) \subseteq R$ for every $f \in L^{1} (G)$ satisfying $f = f^{*}$ , and called quasi-Hermitian if…

math.OA2017

Kirchberg's factorization property for locally compact groups

Matthew Wiersma

A locally compact group $G$ has the factorization property if the map $C^{*} (G) ⊙ C^{*} (G) ∋ a \otimes b \mapsto λ (a) ρ (b) \in B (L^{2} (G))$ is continuous with respect to the mi…

math.OA2017★ 7 cited

Existence of tracial states on reduced group C*-algebras

Brian E. Forrest, Nico Spronk, Matthew Wiersma

Let $G$ be a locally compact group. It is not always the case that its reduced C*-algebra $C_{r}^{*} (G)$ admits a tracial state. We exhibit closely related necessary and sufficient con…

math.OA2017

Weak containment by restrictions of induced representations

Matthew Wiersma

A QSIN group is a locally compact group $G$ whose group algebra $L^{1} (G)$ admits a quasi-central bounded approximate identity. Examples of QSIN groups include every amenable group a…

math.OA2015

Weak* tensor products for von Neumann algebras

Matthew Wiersma

The category of $C^{*}$ -algebras is blessed with many different tensor products. In contrast, virtually the only tensor product ever used in the category of von Neumann algebras is t…

math.OA2015★ 2 cited

On exotic group C*-algebras

Zhong-Jin Ruan, Matthew Wiersma

Let $Γ$ be a discrete group. A $C^{*}$ -algebra $A$ is an exotic $C^{*}$ -algebra (associated to $Γ$ ) if there exist proper surjective $C^{*}$ -quotients $C^{*} (Γ) \to A \to C_{r}^{*} (Γ)$ . In this…

math.FA2014★ 3 cited

$L^{p}$ -Fourier and Fourier-Stieltjes algebras for locally compact groups

Matthew Wiersma

Let $G$ be a locally compact group and $1 \leq p < \infty$ . A continuous unitary representation $π : G \to B (H)$ of $G$ is an $L^{p}$ -representation if the matrix coefficient…

math.OA2014★ 11 cited

C-norms for tensor products of discrete group C-algebras

Matthew Wiersma

Let $Γ$ be a discrete group. We show that if $Γ$ is nonamenable, then the algebraic tensor products $C_{r}^{*} (Γ) \otimes C_{r}^{*} (Γ)$ and $C^{*} (Γ) \otimes C_{r}^{*} (Γ)$ do not admit unique $C^*…

math.OA2014★ 3 cited

Exotic group C*-algebras

Matthew Wiersma

Let $Γ$ be a discrete group. When $Γ$ is nonamenable, the reduced and full group $C$ *-algebras differ and it is generally believed that there should be many intermediate $C$ *-algeb…

math.CA2012

Optimal error estimates for corrected trapezoidal rules

Erik Talvila, Matthew Wiersma

Corrected trapezoidal rules are proved for $\int_{a}^{b} f (x) d x$ under the assumption that $f " \in L^{p} ([a, b])$ for some $1 \leq p \leq \infty$ . Such quadrature rules involve the trapezoi…

math.CA2012★ 5 cited

Simple derivation of basic quadrature formulas

Erik Talvila, Matthew Wiersma

Simple proofs of the midpoint, trapezoidal and Simpson's rules are proved for numerical integration on a compact interval. The integrand is assumed to be twice continuously differe…

math.CA2011★ 2 cited

Quadrature rules with (not too many) derivatives

Matthew Wiersma

Quadrature formulas for $\int_{a}^{b} f (x) d x$ where derivative terms need only be evaluated at $a$ and $b$ in the composite rule are identified. Error bounds are given when $f:[a,b]\t…

On operator Connes-amenability of the Fourier-Stieltjes algebra

Entropies and Poisson boundaries of random walks on groups with rapid decay

New tensor products of C*-algebras and characterization of type I C*-algebras as rigidly symmetric C*-algebras

Traces on locally compact groups

Cohomological obstructions to lifting properties for full group C∗-algebras

Exotic C*-algebras of geometric groups

Quasi-Hermitian locally compact groups are amenable

Kirchberg's factorization property for locally compact groups

Existence of tracial states on reduced group C*-algebras

Weak containment by restrictions of induced representations

Weak* tensor products for von Neumann algebras

On exotic group C*-algebras

Lp-Fourier and Fourier-Stieltjes algebras for locally compact groups

C*-norms for tensor products of discrete group C*-algebras

Exotic group C*-algebras

Optimal error estimates for corrected trapezoidal rules

Simple derivation of basic quadrature formulas

Quadrature rules with (not too many) derivatives

New tensor products of C-algebras and characterization of type I C-algebras as rigidly symmetric C*-algebras

Cohomological obstructions to lifting properties for full group C $^{*}$ -algebras

$L^{p}$ -Fourier and Fourier-Stieltjes algebras for locally compact groups

C-norms for tensor products of discrete group C-algebras