paper

Coloured peak algebras and Hopf algebras

arXiv:math/0505612 · doi:10.1007/s10801-006-0009-4

Abstract

For a finite abelian group, we study the properties of general equivalence relations on $G_n=G^n\rtimes \SG_n$, the wreath product of with the symmetric group $\SG_n$, also known as the -coloured symmetric group. We show that under certain conditions, some equivalence relations give rise to subalgebras of $\k G_n$ as well as graded connected Hopf subalgebras of $\bigoplus_{n\ge o} \k G_n$. In particular we construct a -coloured peak subalgebra of the Mantaci-Reutenauer algebra (or -coloured descent algebra). We show that the direct sum of the -coloured peak algebras is a Hopf algebra. We also have similar results for a -colouring of the Loday-Ronco Hopf algebras of planar binary trees. For many of the equivalence relations under study, we obtain a functor from the category of finite abelian groups to the category of graded connected Hopf algebras. We end our investigation by describing a Hopf endomorphism of the -coloured descent Hopf algebra whose image is the -coloured peak Hopf algebra. We outline a theory of combinatorial -coloured Hopf algebra for which the -coloured quasi-symmetric Hopf algebra and the graded dual to the -coloured peak Hopf algebra are central objects.

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