# Global existence in the 1D quasilinear parabolic-elliptic chemotaxis system with critical nonlinearity

## TL;DR

This paper proves the global existence of solutions for the 1D parabolic-elliptic Keller-Segel system with critical nonlinearity, filling a gap left by previous work that only addressed a modified system.

## Contribution

It introduces a new Lyapunov-like functional to establish global solutions for the standard system, extending results beyond the special Jager-Luckhaus case.

## Key findings

- Solutions remain bounded for all initial masses.
- A new Lyapunov-like functional guarantees global existence.
- Addresses a gap in the analysis of the standard Keller-Segel system.

## Abstract

The paper should be viewed as complement of an earlier result in [8]. In the paper just mentioned it is shown that 1d case of a quasilinear parabolic-elliptic Keller-Segel system is very special. Namely, unlike in higher dimensions, there is no critical nonlinearity. Indeed, for the nonlinear diffusion of the form 1/u all the solutions, independently on the magnitude of initial mass, stay bounded. However, the argument presented in [8] deals with the Jager-Luckhaus type system. And is very sensitive to this restriction. Namely, the change of variables introduced in [8], being a main step of the method, works only for the Jager-Luckhaus modification. It does not seem to be applicable in the usual version of the parabolic-elliptic Keller-Segel system. The present paper fulfils this gap and deals with the case of the usual parabolic-elliptic version. To handle it we establish a new Lyapunov-like functional (it is related to what was done in [8]), which leads to global existence of the initial-boundary value problem for any initial mass.