Absence of critical mass phenomena in one-dimensional critical quasilinear Keller-Segel systems

Abstract

We consider the Neumann initial boundary value problem associated to the chemotaxis system \begin{align}\label{prob:abstract}\tag{$\star$} \begin{cases} u_t = \big((u+1)^{m-1} u_x - u(u+1)^m v_x\big)_x & \text{in $(0,1)\times (0,\infty )$}, \\ v_t = v_{xx} - v + u, &\text{in $(0,1)\times (0,\infty )$}, \end{cases} \end{align} where $m\in \mathbb{R}$ is a given parameter. The relation between diffusion and taxis sensitivity is critical since the ratio $u(u+1{)}^m/(u+1{)}^{m-1}$ grows like $u^{2/n}$ for large $u$ with $n=\dim ((0,1))=1$. Nonetheless, we show that there is no critical mass phenomenon if $m\le -1$; that is, in that case all solutions emanating from suitably regular initial data are globally bounded. For certain parabolic-elliptic simplifications of \eqref{prob:abstract}, we obtain the same conclusion for all $m\in (-\infty ,-1]\cup (0,\infty )$ and even for all $m\in \mathbb{R}$ if the initial datum is additionally assumed to be monotone. This stands in contrast to critical mass phenomena known to occur for critical quasilinear Keller-Segel systems considered in higher-dimensional domains. Accordingly, we make use of several special features of the one-dimensional setting such as the boundedness of the energy functional from below, the embedding $W^{1,n}\hookrightarrow L^{\infty }$, and the fact that the mass accumulation function solves a spatially non-degenerate parabolic equation.

20 pages