BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Chris Bruce (Queen Mary University of London) DTSTART:20200708T190000Z DTEND:20200708T200000Z DTSTAMP:20260420T053037Z UID:NYC-NCG/11 DESCRIPTION:Title: C*-algebras from actions of congruence monoids\nby Chris Bruce (Queen Mary University of London) as part of Noncommutative geometry in NYC\n\n\ nAbstract\nI will give an overview of recent results for semigroup C*-alge bras associated with number fields. These results are already interesting in the case where the field is the rational numbers\, and I will focus mos tly on this case to make everything more explicit and accessible.\nC*-alge bras of full ax+b-semigroups over rings of algebraic integers were first s tudied by Cuntz\, Deninger\, and Laca\; their construction has since been generalized by considering actions of congruence monoids. Semigroup C*-alg ebras obtained this way provide an example class of unital\, separable\, n uclear\, strongly purely infinite C*-algebras which\, in many cases\, comp letely characterize the initial number-theoretic data. They also carry can onical time evolutions\, and the associated C*-dynamical systems exhibit i ntriguing phenomena. For instance\, the striking similarity between the K- theory formula and the parameterization space for the low temperature KMS states\, observed by Cuntz in the case of the full ax+b-semigroup\, persis ts in the more general setting.\nPart of this work is joint with Xin Li\, and part is joint with Marcelo Laca and Takuya Takeishi.\n LOCATION:https://researchseminars.org/talk/NYC-NCG/11/ END:VEVENT END:VCALENDAR