On the convexity of the KdV Hamiltonian

Thomas Kappeler, Alberto Maspero, Jan-Cornelius Molnar +1

We prove that the nonlinear part $H^{\ast }$ of the KdV Hamiltonian $H^{kdv}$, when expressed in action variables $I=(I_n{)}_{n\ge 1}$, extends to a real analytic function on the pos…