Constraints of the DΔΔKP hierarchy to the semi-discrete AKNS and Burgers hierarchies

This paper investigates three eigenfunction constraints on the differential-difference Kadomtsev-Petviashvili (DΔ\DeltaKP) hierarchy, demonstrating that a squared eigenfunction constraint yields the semi-discrete AKNS hierarchy while two distinct linear eigenfunction constraints lead to a combined semi-discrete Burgers hierarchy, with all results rigorously proved using recursive algebraic structures generated by master symmetries.

Jin Liu, Da-jun Zhang2026-03-10🌀 nlin

Lagrangian formulation of the Darboux system

This paper establishes that the classical Darboux system admits a scalar Lagrangian formulation equivalent to the generating PDE of the KP hierarchy, extends this framework to differential-difference and fully discrete versions using elementary and special functions respectively, and demonstrates that their dispersionless limits yield a complete classification of 3D second-order integrable Lagrangians.

Lingling Xue, E. V. Ferapontov, M. V. Pavlov2026-03-06🔬 physics

Quantum two-dimensional superintegrable systems in flat space: exact-solvability, hidden algebra, polynomial algebra of integrals

This review paper demonstrates that six specific two-dimensional quantum superintegrable systems in flat space are exactly solvable and share a common hidden Lie algebraic structure, characterized by polynomial eigenfunctions, infinite flags of invariant subspaces, and finite-order polynomial algebras of integrals.

Alexander V Turbiner, Juan Carlos Lopez Vieyra, Pavel Winternitz2026-03-06⚛️ quant-ph