An infinitesimal deformation of the post-Lie and post-Hopf algebra correspondence

@misc{rivezzi2026infinitesimal,
  title = {{An infinitesimal deformation of the post-Lie and post-Hopf algebra correspondence}},
  author = {Andrea Rivezzi and Andrea Sciandra and Thomas Weber},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2607.28009},
  eprint = {2607.28009},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.28009},
  note = {CC BY-NC-ND 4.0},
}

TY  - UNPB
TI  - An infinitesimal deformation of the post-Lie and post-Hopf algebra correspondence
AU  - Andrea Rivezzi
AU  - Andrea Sciandra
AU  - Thomas Weber
PY  - 2026
DA  - 2026/11/03
PB  - arXiv
DO  - 10.48550/arxiv.2607.28009
UR  - https://arxiv.org/abs/2607.28009
AB  - We describe infinitesimal deformations of post-Lie algebras and post-Hopf algebras and prove that the universal enveloping algebra and primitive elements adjunction is compatible with the infinitesimal structure. In characteristic zero, this restricts to an equivalence for connected cocommutative infinitesimal post-Hopf algebras, extending the Cartier--Milnor--Moore theorem. We parametrize all infinitesimal post-Lie structures on sl(2) and exhibit a second-order obstruction. From a geometric point of view, infinitesimal post-Lie algebras emerge from flat connections with covariantly constant torsion and an additional compatible symmetric (1,2)-tensor. This leads to explicit examples of infinitesimal post-Lie structures based on Heisenberg Lie algebras. On the Hopf side, we classify infinitesimal structures above the trivial action, prove rigidity for group algebras, and describe the structures on Sweedler's Hopf algebra. The subadjacent construction induces a Hopf algebra deformation with fixed coproduct. Finally, we prove that the quadratic operad of infinitesimal post-Lie algebras is Koszul, using a filtered distributive law between the operads of Lie algebras and bi-magmas.
ER  -