Colloquia/Fall18: Difference between revisions

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===September 4: Isaac Goldbring (UIC) ===
===September 4: Isaac Goldbring (UIC) ===
Title: Hindman's theorem and idempotent types
Title: On Kirchberg's embedding problem


Abstract: For a set A of natural numbers, let FS(A) denote the set of sums of finitely many distinct elements of A. A set B of natural numbers is said to be an IP set if B contains FS(A) for some infinite set A. A central result in combinatorial number theory is Hindman's theorem, which states that if one finitely colors an IP set, then at least one of the colors is an IP set. The slickest proof of this result uses idempotent ultrafilters. Di Nasso suggested a model-theoretic generalization of idempotent ultrafilters, aptly named idempotent types, and asked in what completions of PA idempotent types exist. In this talk, I will show that Hindman's theorem is actually equivalent to the existence of idempotent types in all countable complete extensions of PA. This is joint work with Uri Andrews.
Abstract: In his seminal work on the classification program for nuclear C*-algebras, Kirchberg showed that a particular C*-algebra, the Cuntz algebra O2, plays a seminal role. Subsequent work with Chris Phillips showed that O2 also plays a prominent role in regards to the wider class of exact C*-algebras, and this led Kirchberg to conjecture that every C*-algebra is finitely representable in O2, that is, is embeddable in an ultrapower of O2. The main goal of this talk is to sketch a proof of a local finitary reformulation of this conjecture of Kirchberg. The proof uses model theory and in particular the notion of model-theoretic forcing. No knowledge of C*-algebras or model theory will be assumed. This is joint work with Thomas Sinclair.


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Revision as of 13:46, 2 September 2015


Mathematics Colloquium

All colloquia are on Fridays at 4:00 pm in Van Vleck B239, unless otherwise indicated.

Fall 2015

Go to next semester, Spring 2016.


date speaker title host(s)
September 4 Isaac Goldbring (UIC) On Kirchberg's embedding problem Andrews/Lempp
September 11 Doron Puder (IAS) Word-Measures on Groups Gurevich
September 18 Izzet Coskun (UIC) The geometry of points in the plane Erman
September 25 Abbas Ourmazd (UW-Milwaukee) Mitchell
October 2
October 9 Igor Mezic (UC Santa Barbara) Budisic, Thiffeault
October 16 Hadi Salmasian (Ottawa) Gurevich
October 23 Wisconsin Science Festival.
October 30 Ruth Charney (Brandeis) Dymarz
November 6 Reserved *S
November 13 Reserved *T
November 20 Reserved
November 27 University Holiday No Colloquium
December 4 Reserved
December 11 Reserved

Abstracts

September 4: Isaac Goldbring (UIC)

Title: On Kirchberg's embedding problem

Abstract: In his seminal work on the classification program for nuclear C*-algebras, Kirchberg showed that a particular C*-algebra, the Cuntz algebra O2, plays a seminal role. Subsequent work with Chris Phillips showed that O2 also plays a prominent role in regards to the wider class of exact C*-algebras, and this led Kirchberg to conjecture that every C*-algebra is finitely representable in O2, that is, is embeddable in an ultrapower of O2. The main goal of this talk is to sketch a proof of a local finitary reformulation of this conjecture of Kirchberg. The proof uses model theory and in particular the notion of model-theoretic forcing. No knowledge of C*-algebras or model theory will be assumed. This is joint work with Thomas Sinclair.

September 11: Doron Puder (IAS)

Title: Word-Measures on Groups.

Abstract: Let w be a word in the free group on k generators, and let G be a finite (compact) group. The word w induces a measure on G by substituting the letters of w with k independent uniformly (Haar) chosen random elements of G and evaluating the product. Questions about word-measures on groups attracted attention in recent years both for their own sake and as a tool to analyze random walks on groups.

We will explain some properties of word-measure, give examples and state conjectures. We will also talk about recent results regarding word-measures on symmetric groups and word-measures on unitary groups.

September 18: Izzet Coskun (UIC)

Title: The geometry of points in the plane

Abstract: Grothendieck's Hilbert scheme of points is a smooth compactification of the configuration space of points in the plane. It has close connections with combinatorics, representation theory, mathematical physics and algebraic geometry. In this talk, I will survey some of the basic properties of this beautiful space. If time permits, I will discuss joint work with Arcara, Bertram and Huizenga on codimension one subvarieties of the Hilbert scheme.

October 9: Igor Mezic (UC Santa Barbara)

Past Colloquia

Spring 2015

Fall 2014

Spring 2014

Fall 2013

Spring 2013

Fall 2012