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Criteria for rational smoothness of some symmetric orbit closures
KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
2010 (engelsk)Inngår i: DMTCS Proceedings, 22nd International Conference on Formal Power Series and Algebraic Combinatorics (FPSAC 2010), 2010, s. 319-330Konferansepaper, Publicerat paper (Fagfellevurdert)
Abstract [en]

Let G be a connected reductive linear algebraic group over ℂ with an involutionθ. Denote by K the subgroup of fixed points. In certain cases, the K-orbits in the flag variety G/B are indexed by the twisted identities ι(θ) = {θ (w -1)w |w ∈ W} in the Weyl group W. Under this assumption, we establish a criterion for rational smoothness of orbit closures which generalises classical results of Carrell and Peterson for Schubert varieties. That is, whether an orbit closure is rationally smooth at a given point can be determined by examining the degrees in a "Bruhat graph" whose vertices form a subset of ι(θ). Moreover, an orbit closure is rationally smooth everywhere if and only if its corresponding interval in the Bruhat order on ι(θ) is rank symmetric. In the special case K = Sp 2n(ℂ), G = SL 2n(ℂ), we strengthen our criterion by showing that only the degree of a single vertex, the "bottom one", needs to be examined. This generalises a result of Deodhar for type A Schubert varieties.

sted, utgiver, år, opplag, sider
2010. s. 319-330
Emneord [en]
Bruhat graph, Rational smoothness, Symmetric orbit
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-150314Scopus ID: 2-s2.0-84860541566OAI: oai:DiVA.org:kth-150314DiVA, id: diva2:742431
Konferanse
22nd International Conference on Formal Power Series and Algebraic Combinatorics, FPSAC'10, 2 August 2010 through 6 August 2010, San Francisco, CA, United States
Merknad

QC 20140901

Tilgjengelig fra: 2014-09-01 Laget: 2014-09-01 Sist oppdatert: 2014-09-01bibliografisk kontrollert

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