Didier Pilod - Finite point blowup for the critical generalized Korteweg-de Vries equation

This talk was part of the Thematic Programme on "Nonlinear Waves and Relativity" held at the ESI April 29 -- June 21, 2024.
In the last twenty years, there have been significant advances in the study of the blow-up phenomenon for the critical generalized Korteweg-de~Vries (gKdV) equation, including the determination of sufficient conditions for blowup, the stability of blowup in a refined topology and the classification of minimal mass blowup. Exotic blow-up solutions with a continuum of blow-up rates and multi-point blow-up solutions were also constructed. However, all these results, as well as numerical simulations, involve the bubbling of a solitary wave going at infinity at the blow-up time, which means that the blow-up dynamics and the residue are eventually uncoupled. Even at the formal level, there was no indication whether blowup at a finite point could occur for this equation.
After reviewing the theory of blow-up for the critical gKdV equation in the first part of the talk, we will answer this question by constructing solutions that blow up in finite time under the form of a single-bubble concentrating the ground state at a finite point with an unforeseen blow-up rate. Finding a blow-up rate intermediate between the self-similar rateand other rates previously known also reopens the question of which blow-up rates are actually possible for this equation.
This talk is based on a joint work with Yvan Martel (Université de Versailles/France).