A new result for boundedness in the quasilinear parabolic-parabolic Keller-Segel model (with logistic source)

TL;DR

This paper establishes new conditions on the diffusion coefficient's growth rate in a Keller-Segel model with logistic source that guarantee the solutions remain bounded globally in time.

Contribution

It provides the first rigorous mathematical relationship between the growth exponent m and the ratio μ/χ ensuring boundedness of solutions.

Findings

Solutions are globally bounded under specific growth conditions on D(u).

Derived explicit bounds relating m, μ, and χ for solution boundedness.

Established new thresholds for the diffusion exponent m in Keller-Segel models.

Abstract

The current paper considers the boundedness of solutions to the following quasilinear Keller-Segel model (with logistic source) $$\left\{\begin{array}{ll} u_t = \nabla\cdot(D(u)\nabla u)-\chi\nabla\cdot(u\nabla v)+\mu (u-u^2),\quad x\in \Omega, t>0,\\ v_t-\Delta v = u-v,\quad x\in \Omega, t>0,\\ (D(u)\nabla u-\chi u\cdot \nabla v)\cdot \nu = \frac{\partial v}{\partial\nu}=0,\quad x\in \partial\Omega, t>0,\\ u(x,0) = u_0(x),\quad v(x,0) = v_0(x),\ \ x\in \Omega, \end{array}\right.$$ where $\Omega\subset\mathbb{R}^N(N\geq1)$ is a bounded domain with smooth boundary $\partial\Omega,$ $\chi>0$ and $\mu\geq0$. We prove that for nonnegative and suitably smooth initial data $(u_0, v_0)$, if $D(u)\geq C_{D}(u+1)^{m-1}$ for all $u\geq 0$ with some $C_{D} > 0$ and some $m>2-\frac{2}{N}\frac{\chi\max\{1,\lambda_0\}}{[\chi\max\{1,\lambda_0\}-\mu]_{+}}$ or $m=2-\frac{2}{N}$ and $C_D>\frac{C_{GN}(1+\|u_0\|_{L^1(\Omega)})}{3}(2-\frac{2}{N})^2\max\{1,\lambda_0\}\chi$, the $(KS)$ possesses a global classical solution which is bounded in $\Omega\times (0,\infty)$, where $C_{GN}$ and $\lambda_0$ are the constants which are corresponding to the Gagliardo--Nirenberg inequality and the maximal Sobolev regularity. To our best knowledge, this seems to be the first rigorous mathematical result which (precisely) gives the relationship between $m$ and $\frac{\mu}{\chi}$ that yields to the boundedness of the solutions.