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On the complex and convex geometry of Ol'shanskii semigroups

Karl-Hermann Neeb — 1998

Annales de l'institut Fourier

To a pair of a Lie group G and an open elliptic convex cone W in its Lie algebra one associates a complex semigroup S = G Exp ( i W ) which permits an action of G × G by biholomorphic mappings. In the case where W is a vector space S is a complex reductive group. In this paper we show that such semigroups are always Stein manifolds, that a biinvariant domain D S is Stein is and only if it is of the form G Exp ( D h ) , with D h i W convex, that each holomorphic function on D extends to the smallest biinvariant Stein domain containing D ,...

Globality in semisimple Lie groups

Karl-Hermann Neeb — 1990

Annales de l'institut Fourier

In the first section of this paper we give a characterization of those closed convex cones (wedges) W in the Lie algebra s l ( 2 , R ) n which are invariant under the maximal compact subgroup of the adjoint group and which are controllable in the associated simply connected Lie group S l ( 2 , R ) n , i.e., for which the subsemigroup S = ( exp W ) generated by the exponential image of W agrees with the whole group G (Theorem 13). In Section 2 we develop some algebraic tools concerning real root decompositions with respect to compactly...

On the complex geometry of invariant domains in complexified symmetric spaces

Karl-Hermann Neeb — 1999

Annales de l'institut Fourier

Let M = G / H be a real symmetric space and 𝔤 = 𝔥 + 𝔮 the corresponding decomposition of the Lie algebra. To each open H -invariant domain D 𝔮 i 𝔮 consisting of real ad-diagonalizable elements, we associate a complex manifold Ξ ( D 𝔮 ) which is a curved analog of a tube domain with base D 𝔮 , and we have a natural action of G by holomorphic mappings. We show that Ξ ( D 𝔮 ) is a Stein manifold if and only if D 𝔮 is convex, that the envelope of holomorphy is schlicht and that G -invariant plurisubharmonic functions correspond to convex H -invariant...

Central extensions of infinite-dimensional Lie groups

Karl-Hermann Neeb — 2002

Annales de l’institut Fourier

The main result of the present paper is an exact sequence which describes the group of central extensions of a connected infinite-dimensional Lie group G by an abelian group Z whose identity component is a quotient of a vector space by a discrete subgroup. A major point of this result is that it is not restricted to smoothly paracompact groups and hence applies in particular to all Banach- and Fréchet-Lie groups. The exact sequence encodes in particular precise obstructions for a given Lie algebra...

Non-abelian extensions of infinite-dimensional Lie groups

Karl-Hermann Neeb — 2007

Annales de l’institut Fourier

In this article we study non-abelian extensions of a Lie group G modeled on a locally convex space by a Lie group N . The equivalence classes of such extension are grouped into those corresponding to a class of so-called smooth outer actions S of G on N . If S is given, we show that the corresponding set Ext ( G , N ) S of extension classes is a principal homogeneous space of the locally smooth cohomology group H s s 2 ( G , Z ( N ) ) S . To each S a locally smooth obstruction class χ ( S ) in a suitably defined cohomology group H s s 3 ( G , Z ( N ) ) S is defined....

Lie group extensions associated to projective modules of continuous inverse algebras

Karl-Hermann Neeb — 2008

Archivum Mathematicum

We call a unital locally convex algebra A a continuous inverse algebra if its unit group A × is open and inversion is a continuous map. For any smooth action of a, possibly infinite-dimensional, connected Lie group G on a continuous inverse algebra A by automorphisms and any finitely generated projective right A -module E , we construct a Lie group extension G ^ of G by the group GL A ( E ) of automorphisms of the A -module E . This Lie group extension is a “non-commutative” version of the group Aut ( 𝕍 ) of automorphism...

Finite-dimensional Lie subalgebras of algebras with continuous inversion

Daniel BeltiţăKarl-Hermann Neeb — 2008

Studia Mathematica

We investigate the finite-dimensional Lie groups whose points are separated by the continuous homomorphisms into groups of invertible elements of locally convex algebras with continuous inversion that satisfy an appropriate completeness condition. We find that these are precisely the linear Lie groups, that is, the Lie groups which can be faithfully represented as matrix groups. Our method relies on proving that certain finite-dimensional Lie subalgebras of algebras with continuous inversion commute...

On the cohomology of vector fields on parallelizable manifolds

Yuly BilligKarl-Hermann Neeb — 2008

Annales de l’institut Fourier

In the present paper we determine for each parallelizable smooth compact manifold M the second cohomology spaces of the Lie algebra 𝒱 M of smooth vector fields on M with values in the module Ω ¯ M p = Ω M p / d Ω M p - 1 . The case of p = 1 is of particular interest since the gauge algebra of functions on M with values in a finite-dimensional simple Lie algebra has the universal central extension with center Ω ¯ M 1 , generalizing affine Kac-Moody algebras. The second cohomology H 2 ( 𝒱 M , Ω ¯ M 1 ) classifies twists of the semidirect product of 𝒱 M with the...

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