Groups acting simply transitively on the vertices of a building of type \(\tilde A_ 2\). I. (English) Zbl 0784.51010

Let \(K\) denote a not necessarily commutative field with discrete valuation. For each \(n \geq 2\) there is a building \(\Delta\) of type \(\tilde A_{n-1}\) on which \({\mathcal G}= \text{PGL}(n,K)\) acts. For the case \(n=2\) see M. Ronan, ‘Lectures on buildings’, Academic Press, New York (1989; Zbl 0694.51001). The authors of the present article consider the case \(n=3\), motivated by the case when \(\Delta\) is the building of \({\mathcal G}= \text{PGL}(3,K)\), \(K\) is a local field, and when \(\Gamma \leq{\mathcal G}\), where \(\Gamma\) is a group acting simply transitively on the vertices of an affine building \(\Delta\).
The authors consider general buildings \(\Delta\) and show that if \(\Delta\) admits a group \(\Gamma\) of automorphisms, then \(\Delta\) must have a diagram of very restricted type. Thereafter, they consider only thick affine buildings \(\Delta\) and assume that their group \(\Gamma\) consists of type-rotating automorphisms of \(\Delta\). They show that there is point-line correspondence \(\lambda:P \to L\) and a triangle presentation \(T\) compatible with \(\lambda\) such that \(\Gamma=\{\{g_ x\}_{x \in P} \mid g_ xg_ yg_ z=1\) for each \((x,y,z) \in T \}\), where \(L\) and \(P\) are sets of neighbours of types 1 and 2, respectively, of a fixed vertex \(v_ 0\) of type 0 and \(g_ x\) is the unique element of \(\Gamma\) such that \(g_ x v_ 0=x\). Then the authors consider the Desarguesian projective plane \((P,L)\) of order \(q\), where \(q\) is any prime power and give a point-line correspondence \(\lambda_ 0:P \to L\) and compatible triangle representation \(T_ 0\). Modifying construction of Tits they embed the associated group \(\Gamma_ 0\) in \({\mathcal G}=\text{PGL} \biggl( 3,F_ q \bigl(( X) \bigr) \biggr)\), where it acts simply transitively on vertices of \(\Delta\). They construct all triangle presentations whose symmetry groups are similarly large as symmetry group of \(T_ 0\) and suppose that it is not clear whether all associate groups \(\Gamma_ T\) arise as subgroups of matrix groups. It is essential that triangle presentations mentioned above give rise to some new building of type \(\tilde A_ 2\).
Reviewer: P.Burda (Ostrava)


51E24 Buildings and the geometry of diagrams
51E15 Finite affine and projective planes (geometric aspects)
20G25 Linear algebraic groups over local fields and their integers
20F05 Generators, relations, and presentations of groups


Zbl 0694.51001
Full Text: DOI


[1] Albert, A. A.,Structure of Algebras, Amer. Math. Soc. Colloq. Publications, Vol. XXIV, Amer. Math. Soc. 1939. · Zbl 0023.19901
[2] Betori, W. and Pagliacci, M., ?Harmonic analysis for groups acting on trees?,Boll. Un. Mat. Ital. 3-B (1984), 333-349. · Zbl 0579.43014
[3] Brown, K. S.,Buildings, Springer-Verlag, 1989.
[4] Figá-Talamanca, A. and Nebbia, C., ?Harmonic analysis and representation theory for groups acting on homogeneous trees?,London Mathematical Society Lecture Note Series 162, Cambridge University Press, 1991.
[5] Figá-Talamanca, Picardello, M. A., ?Harmonic analysis on free groups?,Lecture Notes in Pure and Applied Mathematics, Marcel Dekker, New York, 1983. · Zbl 0536.43001
[6] Kantor, W. M., ?Generalized polygons, SCABs and GABs?, inBuildings and the Geometry of Diagrams (L. A. Rosati, ed.),Lecture Notes in Math. 1181, Springer Verlag, 1970. pp. 79-158.
[7] Köhler, P., Meixner, T. and Wester, M., ?The affine building of typeà 2 over a local field of characteristic 2?,Archiv Math. 42 (1984), 400-407. · Zbl 0546.20028 · doi:10.1007/BF01190688
[8] Margulis, G. A., ?Discrete subgroups of semisimple Lie groups?,Ergeb. Math. Grenzgeb. (3), Band 17, Springer-Verlag, 1989. · Zbl 0675.10010
[9] Prasad, G., ?Lattices in semisimple groups over local fields?, in ?Studies in Algebra and Number Theory? (G. Rota, ed.), Advances in Mathematics Supplementary Studies, Vol. 6, Academic Press, New York, 1979.
[10] Ronan, M.,Lectures on Buildings, Academic Press, New York, 1989. · Zbl 0694.51001
[11] Serre, J.,Trees, Springer-Verlag, 1980. · Zbl 0548.20018
[12] Tits, J., ?Sur le groupe des automorphismes d’un arbre?, inEssays on Topology and Related Topics, Memoires dédiés à G. de Rham, Springer-Verlag, 1970, pp. 188-211.
[13] Tits, J., ?Buildings and group amalgamations?, inProc. of Groups-St. Andrews, 1985, pp. 110-127 (E. F. Robertson and C. M. Campbell, eds);London Mathematical Society Lecture Note Series 121, Cambridge University Press, 1986.
[14] Tits, J., ?A local approach to buildings?, inThe Geometric Vein. The Coxeter Festschrift, Springer Verlag, New York, Heidelberg, Berlin, 1981 pp. 519-547.
[15] Weil, A., ?Basic number theory?,Grundlehren Math. Wiss. 144, Springer-Verlag, 1974. · Zbl 0326.12001
[16] Zimmer, R. J.,Ergodic Theory and Semisimple Groups, Birkhäuser, 1984. · Zbl 0571.58015
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. In some cases that data have been complemented/enhanced by data from zbMATH Open. This attempts to reflect the references listed in the original paper as accurately as possible without claiming completeness or a perfect matching.