Spectral analysis for singularity formation of the two dimensional Keller-Segel system

TL;DR

This paper conducts a spectral analysis of an operator related to singular solutions in the 2D Keller-Segel system, using asymptotic expansions to describe eigenvalues and eigenfunctions, and proving stability and coercivity results.

Contribution

It provides a rigorous spectral analysis near singular stationary states, extending previous work and addressing the challenges of a singular limit and logarithmic corrections.

Findings

Precise eigenvalues and eigenfunctions characterized

Stability results established for perturbations

Coercivity estimate for non-radial components obtained

Abstract

We analyse an operator arising in the description of singular solutions to the two-dimensional Keller-Segel problem. It corresponds to the linearised operator in parabolic self-similar variables, close to a concentrated stationary state. This is a two-scale problem, with a vanishing thin transition zone near the origin. Via rigorous matched asymptotic expansions, we describe the eigenvalues and eigenfunctions precisely. We also show a stability result with respect to suitable perturbations, as well as a coercivity estimate for the non-radial part. These results are used as key arguments in a new rigorous proof of the existence and refined description of singular solutions for the Keller-Segel problem by the authors. The present paper extends the result by Dejak, Lushnikov, Yu, Ovchinnikov and Sigal [Physica D, 2012]. Two major difficulties arise in the analysis: this is a singular limit problem, and a degeneracy causes corrections not being polynomial but logarithmic with respect to the main parameter.