332 research outputs found
Automorphism groups of right-angled buildings: simplicity and local splittings
We show that the group of type-preserving automorphisms of any irreducible
semi-regular thick right-angled building is abstractly simple. When the
building is locally finite, this gives a large family of compactly generated
(abstractly) simple locally compact groups. Specializing to appropriate cases,
we obtain examples of such simple groups that are locally indecomposable, but
have locally normal subgroups decomposing non-trivially as direct products.Comment: 26 pages. Several points were clarified and a few lemmas were added,
in accordance with the referee's repor
A uniform bound on the nilpotency degree of certain subalgebras of Kac-Moody algebras
Let be a Kac-Moody algebra and be Borel subalgebras of opposite signs. The intersection
is a finite-dimensional
solvable subalgebra of . We show that the nilpotency degree of
is bounded from above by a constant depending
only on . This confirms a conjecture of Y. Billig and A. Pianzola
\cite{BilligPia95}
Bipolar Coxeter groups
We consider the class of those Coxeter groups for which removing from the
Cayley graph any tubular neighbourhood of any wall leaves exactly two connected
components. We call these Coxeter groups bipolar. They include both the
virtually Poincare duality Coxeter groups and the infinite irreducible
2-spherical ones. We show in a geometric way that a bipolar Coxeter group
admits a unique conjugacy class of Coxeter generating sets. Moreover, we
provide a characterisation of bipolar Coxeter groups in terms of the associated
Coxeter diagram.Comment: 25 pages, 2 figure
A sixteen-relator presentation of an infinite hyperbolic Kazhdan group
We provide an explicit presentation of an infinite hyperbolic Kazhdan group
with generators and relators of length at most . That group acts
properly and cocompactly on a hyperbolic triangle building of type .
We also point out a variation of the construction that yields examples of
lattices in -buildings admitting non-Desarguesian residues of
arbitrary prime power order.Comment: 9 pages, 1 figur
Amenable groups and Hadamard spaces with a totally disconnected isometry group
Let be a locally compact Hadamard space and be a totally disconnected
group acting continuously, properly and cocompactly on . We show that a
closed subgroup of is amenable if and only if it is (topologically locally
finite)-by-(virtually abelian). We are led to consider a set \bdfine X which
is a refinement of the visual boundary \bd X. For each x \in \bdfine X, the
stabilizer is amenable.Comment: 15 page
Rank one isometries of buildings and quasi-morphisms of Kac-Moody groups
Given an irreducible non-spherical non-affine (possibly non-proper) building
, we give sufficient conditions for a group G < \Aut(X) to admit an
infinite-dimensional space of non-trivial quasi-morphisms. The result applies
to all irreducible (non-spherical and non-affine) Kac-Moody groups over
integral domains. In particular, we obtain finitely presented simple groups of
infinite commutator width, thereby answering a question of Valerii G. Bardakov
from the Kourovka notebook. Independently of these considerations, we also
include a discussion of rank one isometries of proper CAT(0) spaces from a
rigidity viewpoint. In an appendix, we show that any homogeneous quasi-morphism
of a locally compact group with integer values is continuous.Comment: 19 pages; some typos have been corrected and the list of references
update
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