BEGIN:VCALENDAR
CALSCALE:GREGORIAN
METHOD:PUBLISH
PRODID:-//github.com/rianjs/ical.net//NONSGML ical.net 4.0//EN
VERSION:2.0
X-FROM-URL:https://eom.sdu.dk/events/ical/f2cd3817-f9e5-4881-bea0-3d2cd20d
 5609
X-WR-CALNAME:QM Research Seminar: Condensable Defects in 4D Dijkgraaf-Witt
 en Models
BEGIN:VTIMEZONE
TZID:Europe/Copenhagen
X-LIC-LOCATION:Europe/Copenhagen
BEGIN:DAYLIGHT
DTSTAMP:20260602T163105Z
DTSTART:20261028T030000
SEQUENCE:0
TZNAME:CEST
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
UID:1a2b5ec8-3e7b-4f5e-9153-f6ee2a08c8d2
END:DAYLIGHT
BEGIN:STANDARD
DTSTAMP:20260602T163105Z
DTSTART:20260325T020000
SEQUENCE:0
TZNAME:CEST
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
UID:363876f4-da27-4ed2-90f8-f998fc72d7cd
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
DESCRIPTION:[b]Speaker: Hao Xu[/b]\n(Georg-August University of Göttingen)
  \n\n\n[b]Abstract:[/b] Given a finite symmetry group $G$ with an anomaly
  $\pi \in \mathrm{H}^4(G\,U(1))$\, one can construct a twisted 4D gauge t
 heory called a Dijkgraaf-Witten model. These models are exactly solvable 
 and play important roles in both higher energy physics and topological or
 ders of quantum phases of matter. People have previously studied (codim >
  1) topological defects (such as generalizations of Wilson lines) within 
 them\, which together form a **braided fusion 2-category**\, $\mathscr{Z}
 (\mathbf{2Vect}^\pi_G)$\, the Drinfeld center of $\pi$-twisted $G$-crosse
 d finite semisimple linear categories.\nAnyons (i.e. topological line def
 ects) can condense in 3D quantum systems to produce new ones\, with gappe
 d 2D domain walls sitting between these 3D systems. It has been known for
  a decade that such a physical process can be described mathematically co
 nsidering connected étale algebras (which in physical terms correspond to
  a condensable set of anyons)\, their ordinary and local modules within m
 odular tensor categories. In particular\, the after-condensation phase is
  trivial if and only if the condensable set of anyons is maximal\, and he
 nce the gapped 2D domain wall becomes a 2D topological boundary of the or
 iginal phase. \nMy doctoral project is to develop a mathematical framewor
 k for the same picture but in one higher dimension. This goal has been ac
 hieved with Décoppet in a series of past papers\, where we define **étale
  algebras** and their **local modules** in braided fusion 2-categories an
 d study their properties. In a recent independent work\, I applied the ge
 neral machinery to $\mathscr{Z}(\mathbf{2Vect}^\pi_G)$\, where étale alge
 bras mean $\pi$-twisted $G$-crossed braided multifusion 1-categories. Bui
 lt upon essential tools developed by Drinfeld et al.\, I obtain a **class
 ification of connected étale algebras** in $\mathscr{Z}(\mathbf{2Vect}^\p
 i_G)$. In particular\, Lagrangian algebras in $\mathscr{Z}(\mathbf{2Vect}
 ^\pi_G)$ correspond to 3D topological boundaries of 4D Dijkgraaf-Witten M
 odels. \nDécoppet has shown that the Drinfeld center of an arbitrary fusi
 on 2-category is either equivalent to a 4D Dijkgraaf-Witten model $\maths
 cr{Z}(\mathbf{2Vect}^\pi_G)$ or a more complicated fermionic version. If 
 time allows\, I would introduce my classification result for all **fusion
  2-categories** based on studying Lagrangian algebras in 4D Dijkgraaf-Wit
 ten models.
DTEND:20250317T150000Z
DTSTAMP:20260602T163105Z
DTSTART:20250317T140000Z
LOCATION:Syddansk Universitet\, Campusvej 55\, 5230\, Odense M
SEQUENCE:0
SUMMARY:QM Research Seminar: Condensable Defects in 4D Dijkgraaf-Witten Mo
 dels
UID:a0329006-68e7-42cc-8f59-2fdf7fe3e333
END:VEVENT
END:VCALENDAR