2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76334We investigate nonlinear dynamics near an unstable constant equilibrium in the classical Keller-Segel model. Given any general perturbation of magnitude $δ$, we prove that its nonlinear evolution is dominated by the corresponding linear dynamics along a fixed finite number of fastest growing modes, over a time period of $ln(1/δ)$. Our result can be interpreted as a rigourous mathematical characterization for early pattern formation in the Keller-Segel model.Analysis of PDEstext