Optimal critical mass in the two dimensional Keller–Segel model in R2

Abstract The Keller–Segel system describes the collective motion of cells that are attracted by a chemical substance and are able to emit it. In its simplest form it is a conservative drift-diffusion equation for the cell density coupled to an elliptic equation for the chemo-attractant concentration. It is known that, in two space dimensions, for small initial mass there is global existence of classical solutions and for large initial mass blow-up occurs. In this Note we complete this picture and give an explicit value for the critical mass when the system is set in the whole space. To cite this article: J. Dolbeault, B. Perthame, C. R. Acad. Sci. Paris, Ser. I 339 (2004).