The Universal Post-Lie-Rinehart Algebra of Planar Aromatic Trees
Ludwig Rahm
TL;DR
This work constructs the universal free object in the category of tracial post-Lie-Rinehart algebras by extending aromatic-B-series machinery to the post-Lie-Rinehart setting. It introduces planar aromatic trees and a Guin-Oudom extension framework to model endomorphisms, obtaining a concrete free object $\mathcal{APT}=S(\mathcal{PA})\otimes Lie(\mathcal{PT})$ with a tracial post-Lie-Rinehart structure and a decomposable endomorphism algebra that is freely generated over $S(\mathcal{PA})$. The freeness is established through a detailed universality construction using maps $\zeta,\beta,\gamma$ that extend any generating-set map to a morphism, guaranteeing unique factorization. The results connect to post-Lie algebroids and homogeneous-space examples, illustrating how planar-aromatic techniques generalize aromatic B-series to curved spaces and providing a robust algebraic framework for universal objects in this category.
Abstract
This paper defines the algebraic structure of tracial post-Lie-Rinehart algebras and describes the free object in this category. Post-Lie-Rinehart algebras is a generalisation of pre-Lie-Rinehart algebras, and of post-Lie algebroids.
