Boundedness in a quasilinear fully parabolic Keller-Segel system of higher dimension with logistic source

This paper deals with the higher dimension quasilinear parabolic-parabolic Keller-Segel system involving a source term of logistic type $u_t=\nabla\cdot(\phi(u)\nabla u)-\chi\nabla\cdot(u\nabla v)+g(u)$, $\tau v_t=\Delta v-v+u$ in $\Omega\times (0,T)$, subject to nonnegative initial data and homogeneous Neumann boundary condition, where $\Omega$ is smooth and bounded domain in $\mathbb{R}^n$, $n\ge 2$, $\phi$ and $g$ are smooth and positive functions satisfying $ks^p\le\phi$ when $s\ge s_0>1$, $g(s) \le as - \mu s^2$ for $s>0$ with $g(0)\ge0$ and constants $a\ge 0$, $\tau,\chi,\mu>0$. It was known that the model without the logistic source admits both bounded and unbounded solutions, identified via the critical exponent $\frac{2}{n}$. On the other hand, the model is just a critical case with the balance of logistic damping and aggregation effects, for which the property of solutions should be determined by the coefficients involved. In the present paper it is proved that there is $\theta_0>0$ such that the problem admits global bounded classical solutions, regardless of the size of initial data and diffusion whenever $\frac{\chi}{\mu}<\theta_0$. This shows the substantial effect of the logistic source to the behavior of solutions.