Rooted trees and symmetric functions: Zhao’s homomorphism and the commutative hexagon

Keywords: Connes-Kreimer Hopf algebra, rooted trees, planar rooted trees, quasi-symmetric functions, noncommutative symmetric functions MR Classifications: Primary 05C05, 16W30; Secondary 81T15 Recent work in perturbative quantum field theory has led to much study of the Connes-Kreimer Hopf algebra. Its (graded) dual, the Grossman-Larson Hopf algebra of rooted trees, had already been studied by algebraists. L. Foissy introduced a noncommutative version of the Connes-Kreimer Hopf algebra, which turns out to be self-dual. Using some homomorphisms defined by the author and W. Zhao, we describe a commutative diagram that relates the aforementioned Hopf algebras to each other and to the Hopf algebras of symmetric functions, noncommutative symmetric functions, and quasi-symmetric functions. 1