BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Emily Cliff (Sherbrooke University) DTSTART:20230421T140000Z DTEND:20230421T150000Z DTSTAMP:20260423T024552Z UID:CIRGET/91 DESCRIPTION:Title: Smooth 2-groups and their principal bundles\nby Emily Cliff (Sherbrook e University) as part of CRM - Séminaire du CIRGET / Géométrie et Topol ogie\n\nLecture held in PK-5115.\n\nAbstract\nA 2-group is a categorical g eneralization of a group: it's a category with a multiplication operation which satisfies the usual group axioms only up to coherent isomorphisms. I n this talk I will introduce the category of Lie groupoids and bibundles b etween them\, in order to provide the definition of a smooth 2-group. I wi ll define principal bundles for such a smooth 2-group\, and provide classi fication results that allow us to compare them to principal bundles for or dinary groups. As a consequence in specific settings\, we obtain a categor ification of the Freed--Quinn line bundle over the moduli stack Bun_G(X) f or a finite group G and Riemann surface X. This is a line bundle which pla ys an important role in Dijkgraaf--Witten theory (i.e. Chern--Simons theo ry for the finite group G). This talk is based on joint work with Dan Berw ick-Evans\, Laura Murray\, Apurva Nakade\, and Emma Phillips. I will not a ssume any previous background on 2-groups\, Lie groupoids\, or Dijkgraaf-- Witten theory.\n\nNote that we have 2 talks this week\, one at 10 am (E. C liff)\, another one at 11 am (A. Adem).\n LOCATION:https://researchseminars.org/talk/CIRGET/91/ END:VEVENT END:VCALENDAR