Unconditional Well-posedness for the MMT Equation on the Torus

We consider the initial value problem (IVP) for a two-parameter family of derivative nonlinear Schrödinger equations on the torus, known as the Majda-McLaughlin-Tabak (MMT) model arising in weak wave turbulence theory.

For positive derivative order, we show that the flow map is not $C^3$ at the origin.

Using an enhanced energy method, we prove unconditional local well-posedness in Sobolev spaces.

At the energy regularity, conservation of the Hamiltonian and a mass-type quantity yields unconditional global well-posedness.