We prove pointwise-in-time dispersive estimates for solutions to the generalized Korteweg--de Vries (gKdV) equation. In particular, for solutions to the mass-critical model, we assume only that initial data lie in Ḣ^1{4} Ḣ^-1{12} and show that solutions decay in L^ like |t|^-1{3}. To accomplish this, we develop a persistence of negative regularity for solutions to gKdV and extend Lorentz--Strichartz estimates to the mixed norm case.
Kowalski et al. (Thu,) studied this question.