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About
President
Governance
Partner Institutions
Visit
People
Management
Faculty
Postdocs
Visiting Scholars
Staff
Research
Research Groups
Courses
Seminars
Join Us
Faculty
Postdocs
Students
Events
Conferences
Workshops
Forum
Life @ BIMSA
Accommodation
Transportation
Facilities
Tour
News
News
Announcement
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Qiuzhen College, Tsinghua University
Yau Mathematical Sciences Center, Tsinghua University (YMSC)
Tsinghua Sanya International  Mathematics Forum (TSIMF)
Shanghai Institute for Mathematics and  Interdisciplinary Sciences (SIMIS)
BIMSA > BIMSA TQFT and Higher Symmetries Seminar Condensable Defects in 4D Dijkgraaf-Witten Models
Condensable Defects in 4D Dijkgraaf-Witten Models
Organizers
Ansi Bai , Chun Chen , Liang Kong , Yi Long Wang , Zhi Hao Zhang , Hao Zheng
Speaker
Hao Xu
Time
Tuesday, April 1, 2025 4:00 PM - 6:00 PM
Venue
A3-1-301
Online
Zoom 468 248 1222 (BIMSA)
Abstract
Given a finite symmetry group G with anomaly π∈H4(G,U(1)), the 4D Dijkgraaf–Witten model provides an exactly solvable gauge theory with applications in high-energy physics and topological phases of matter. The topological defects in these models form a braided fusion 2-category Z(2VectGπ), the Drinfeld center of π-twisted G-crossed finite semisimple linear categories.
Extending the theory of anyon condensation in 3D, my work (in collaboration with Décoppet) develops a higher-dimensional framework using étale algebras and their local modules in braided fusion 2-categories. In particular, I classify connected étale algebras in Z(2VectGπ), which correspond to twisted G-crossed braided multifusion categories.
Additionally, Décoppet has shown that the Drinfeld center of any fusion 2-category is either a 4D Dijkgraaf–Witten model or a fermionic analogue. Time permitting, I will also discuss classification results for fusion 2-categories via the study of Lagrangian algebras.
Beijing Institute of Mathematical Sciences and Applications
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