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SIGMA 3 (2007), 111, 17 pages arXiv:0708.3180
https://doi.org/10.3842/SIGMA.2007.111
Contribution to the Proceedings of the 2007 Midwest Geometry Conference in honor of Thomas P. Branson
Curved Casimir Operators and the BGG Machinery
Andreas Cap a, b and Vladimír Soucek c
a) Fakultät für Mathematik, Universität Wien, Nordbergstr. 15, A-1090 Wien, Austria
b) International Erwin Schrödinger Institute for Mathematical Physics,
Boltzmanngasse 9, A-1090 Wien, Austria
c) Mathematical Institute, Charles University, Sokolovská 83, Praha, Czech Republic
Received August 24, 2007, in final form November 16, 2007; Published online November 22, 2007
Abstract
We prove that the Casimir operator acting on sections of a
homogeneous vector bundle over a generalized flag manifold naturally
extends to an invariant differential operator on arbitrary parabolic
geometries. We study some properties of the resulting invariant
operators and compute their action on various special types of
natural bundles. As a first application, we give a very general
construction of splitting operators for parabolic geometries. Then
we discuss the curved Casimir operators on differential forms with
values in a tractor bundle, which nicely relates to the machinery of
BGG sequences. This also gives a nice interpretation of the
resolution of a finite dimensional representation by (spaces of
smooth vectors in) principal series representations provided by a
BGG sequence.
Key words:
induced representation; parabolic geometry; invariant differential operator; Casimir operator; tractor bundle; BGG sequence.
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