Hamiltonians with high-order integrals and the ‘‘weak-Painlevé’’ concept

Abstract
We examine the singularity structure of the equations of motion associated to integrable two-dimensional Hamiltonians with second integrals of order higher than 2. We show in these specific examples that the integrability is associated to a singularity expansion of the ‘‘weak-Painlevé’’ type. New cases of integrability are discovered, with still higher-order integrals which are explicitly computed.