Inviscid limit for the hyperbolic Keller--Segel equations in $B_{\infty,1}^{1}$
In this paper, we study the inviscid limit for the hyperbolic Keller--Segel equations with logistic sensitivity $1-u$. We establish a common existence time and a priori estimates uniform with respect to the diffusion coefficient in the critical Besov spaces $B_{p,1}^{1+d/p}(R^d)$ with $1\le p\le\infty$. For $1<p<\infty$, we obtain explicit convergence rates in $B_{p,1}^{0}$, and we also give estimates for the case $p=1$. For initial data in $B_{\infty,1}^{1}$, we prove convergence at rate $O(\varepsilon^{1/2})$ in $L^\infty$, a bound of order $O(\varepsilon^{1/2}\log(e/\varepsilon))$ in $B_{\infty,1}^{0}$, and strong convergence in $L^\infty(0,T;B_{\infty,1}^{1})$. Additional regularity of the initial data yields improved convergence rates. We construct a fixed initial datum showing that the exponent $1/2$ in $L^\infty$ is optimal.