Top-level heading

Projections of nilpotent orbits in simple Lie algebras

Categoria
Seminari di Algebra e Geometria
Data e ora inizio evento
Data e ora fine evento
Aula
Sala di Consiglio
Sede

Dipartimento di Matematica Guido Castelnuovo, Università Sapienza Roma

Speaker
Dmitri Panyushev
Let \( G \) be a simple algebraic group and \( \mathcal O \subset \mathfrak g = Lie(G) \) a nilpotent orbit. If \( H \) is a reductive subgroup of \( G \), then \( \mathfrak g = \mathfrak h \oplus \mathfrak m \), where \( \mathfrak m = \mathfrak h^\perp \). We consider the natural projections \( \varphi : \overline{\mathcal O} \to \mathfrak h \) and \( \psi : \overline{\mathcal O} \to \mathfrak m \) and two related properties of \( (H, \mathcal O) \): \( (P_1) \): \( \mathcal O \cap \mathfrak m = \{0\} \); \( (P_2) \): \( H \) has a dense orbit in \( \mathcal O \). We prove that \( (P_1) \Rightarrow (P_2) \) for all \( \mathcal O \) and the converse holds for \( \mathcal O_{min} \), the minimal nilpotent orbit. If \( (P_1) \) holds, then \( \varphi \) is finite and \( [\varphi(e), \psi(e)] = 0 \) for all \( e \in \mathcal O \). Here \( \overline{\varphi(\mathcal O)} \) is the closure of a nilpotent \( H \)-orbit \( \mathcal O' \) and the orbits \( \mathcal O \) and \( O' \) are “shared” in the sense of Brylinski–Kostant (1994). We provide a classification of all pairs \( (H, \mathcal O) \) with property \( (P_1) \) and discuss relations between \( O \) and \( O' \). In particular, we point out an omission in the list of “shared” orbits. This seminar is part of the activities of the Dipartimento di Eccellenza CUP B83C23001390001 and it is funded by the European Union – Next Generation EU.
Contatti/Organizzatori
bravi@mat.uniroma1.it