An improvement toward global boundedness in a fully parabolic chemotaxis with singular sensitivity in any dimension

Abstract: We are concerned with the following chemotaxis system \begin{equation*} \begin{cases} u_t = \Delta u -\chi \nabla \cdot \left ( \frac{u}{v} \nabla v\right ), v_t = \Delta v -u+ v, \end{cases} \end{equation*} in an open bounded domain with smooth boundary $\Omega \subset \mathbb{R}^n$ with $n \geq 3$. It is known that solutions are globally bounded when $0<\chi< \sqrt{ \frac{2}{n}}$. In this paper, by considering the following energy functional \begin{align*} F_\lambda(u,v)= \int_\Omega \frac{u^p}{v^r} + \lambda \int_\Omega \frac{|\nabla v|^{2p}}{v^{p+r}} + \int_\Omega v^{p-r} \end{align*} for $p>1$, $r= \frac{p-1}{2}$, and $\lambda>0$, we improve this result by showing that there exists $\chi_0>\sqrt{\frac{2}{n}}$ such that for any $\chi \in (0,\chi_0)$, solutions exist globally and remain bounded.