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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
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Forum
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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 > Topics in Representation Theory Quasi-flag manifolds, moment graphs and homotopy Lie groups
Quasi-flag manifolds, moment graphs and homotopy Lie groups
Organizer
Shamil Shakirov
Speaker
Yuri Berest
Time
Thursday, April 3, 2025 1:00 PM - 2:30 PM
Venue
A3-4-301
Online
Zoom 242 742 6089 (BIMSA)
Abstract
In this talk, we will introduce a new class of topological $G$-spaces generalizing the classical flag manifolds $G/T$ of compact connected Lie groups. These spaces --- which we call the m-quasi-flag manifolds $F_m(G,T)$ --- are topological realizations of the rings $Q_m(W)$ of m-quasi-invariant polynomials of finite reflection groups, where $W$ is the Weyl group associated to $(G,T)$. Many properties and geometric structures related to the classical flag manifolds can be extended to quasi-flag manifolds (e.g. equivariant $K$-theory and elliptic cohomology can be computed for quasi-flag manifolds in an explicit way).
In general, the spaces $F_m(G,T)$ can be obtained from $G/T$ by a topological `gluing' construction that we call the m-simplicial thickening. This construction applies to other spaces than $G/T$: e.g., a partial flag manifold, $G/P$, or more generally, an arbitrary GKM manifold M with $G$-action. In this last case, the role of a Weyl group --- or rather, its root system --- is played by the moment graph $\Gamma$ of $M$, to which we can now associate a generalized ring $Q_m(\Gamma)$ of quasi-invariants. Another, perhaps more intriguing generalization, arises when we pass to the $p$-local setting ($p$ a fixed prime) and replace compact Lie groups with p-compact groups (aka homotopy Lie groups). In this case, we obtain topological realizations of algebras of quasi-invariants for some non-Coxeter (complex) reflection groups.
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