Annals of Combinatorics

, Volume 16, Issue 1, pp 1–36 | Cite as

Words and Polynomial Invariants of Finite Groups in Non-Commutative Variables

  • Anouk Bergeron-Brlek
  • Christophe Hohlweg
  • Mike Zabrocki


Let V be a complex vector space with basis {x 1, x 2, . . . , x n } and G be a finite subgroup of GL(V). The tensor algebra T(V) over the complex is isomorphic to the polynomials in the non-commutative variables x 1, x 2, . . . , x n with complex coefficients. We want to give a combinatorial interpretation for the decomposition of T(V) into simple G-modules. In particular, we want to study the graded space of invariants in T(V) with respect to the action of G. We give a general method for decomposing the space T(V) into simple modules in terms of words in a Cayley graph of the group G. To apply the method to a particular group, we require a homomorphism from a subalgebra of the group algebra into the character algebra. In the case of G as the symmetric group, we give an example of this homomorphism from the descent algebra. When G is the dihedral group, we have a realization of the character algebra as a subalgebra of the group algebra. In those two cases, we have an interpretation for the graded dimensions and the number of free generators of the algebras of invariants in terms of those words.

Mathematics Subject Classification

05C25 05E10 20C30 20F55 20F10 


non-commutative invariant theory representation theory finite groups symmetric group dihedral group Cayley graphs words 


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Copyright information

© Springer Basel AG 2011

Authors and Affiliations

  • Anouk Bergeron-Brlek
    • 1
  • Christophe Hohlweg
    • 2
  • Mike Zabrocki
    • 1
  1. 1.Department of Mathematics and StatisticsYork UniversityTorontoCanada
  2. 2.LaCIM, Université du Québec à MontréalMontréal (Québec)Canada

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