Cylindrical contact homology for weakly convex contact forms in dimension three

A contact form $\lambda$ on a closed contact three-manifold $(M,\xi )$ is called weakly convex if either it has no contractible Reeb orbit, or the first Chern class of $\xi$ vanishes on ${\pi }_2(M)$, and the index of every contractible Reeb orbit is at least $2$. We present conditions for a weakly convex contact form to admit a well-defined cylindrical contact homology. The key point is a cancellation mechanism for boundary degenerations involving index-2 Reeb orbits, based on a parity property of holomorphic planes.