TAILIEUCHUNG - Báo cáo toán học: "Affine Weyl groups as infinite permutations"

Tuyển tập các báo cáo nghiên cứu khoa học hay nhất của tạp chí toán học quốc tế đề tài: Affine Weyl groups as infinite permutations. | Affine Weyl groups as infinite permutations Henrik Eriksson Nada KTH S-100 44 Stockholm Sweden henrik@ Kimmo Eriksson Dept. of Mathematics KTH S-100 44 Stockholm Sweden kimmo@ Submitted January 4 1996 Accepted March 23 1998. Abstract We present a unified theory for permutation models of all the infinite families of finite and affine Weyl groups including interpretations of the length function and the weak order. We also give new combinatorial proofs of Bott s formula in the refined version of Macdonald for the Poincare series of these affine Weyl groups. 1991 Mathematics Subject Classification. primary 20B35 secondary 05A15. 1 Introduction The aim of this paper is to present a unified theory for permutation representations of the finite Weyl groups An_ 1 Bn Cn Dn and the affine Weyl groups j4n_1 Bn Cn Dn. Our starting point is the symmetric group Sn the group of permutations of 1 . n . If Sn is presented as the group generated by adjacent transpositions it is isomorphic to the Weyl group An-1 and we obtain well-known interpretations of several Coxeter group concepts in permutation language 1. The Coxeter generators are the adjacent transpositions. 2. Reflections correspond to transpositions. 3. Length-decreasing reflections correspond to inversions. 4. The length of an element K is the number of inversions of K. 5. The weak order relation K Ơ holds if and only if the inversion set of K is included in the inversion set of Ơ. THE ELECTRONIC .JOURNAL OF COmBINATORICS 5 1998 R18 2 We now introduce a mirror at the origin reflecting the points 1. n onto 1. n and we consider permutations of that are mirror symmetric in the sense that they commute with the action of the mirror. The group of such permutations is isomorphic to the Weyl group Cn. Reflection in the origin is a rigid transformation of z and the same game can be played with any group of such rigid transformations. For instance the translation n steps to the right generates a .

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