In this paper, we study the Cauchy problem for the generalized Keller–Segel system with the cell diffusion being ruled by fractional diffusion: $$\begin{aligned} {\left\{ \begin{array}{ll} \partial _{t}u+\Lambda ^{\alpha }u+\nabla \cdot (u\nabla \psi )=0 &{}\quad \text{ in \mathbb {R}^n\times (0,\infty ), -\Delta \psi =u &{}\quad \text{ in \mathbb {R}^n\times (0,\infty ), u(x,0)=u_0(x) &{}\quad \text{ in \mathbb {R}^n. \end{array}\right. } \end{aligned}$$ In the case $$1<\alpha \le 2$$ , we prove local well-posedness for any initial data and global well-posedness for small initial data in critical Besov spaces $$\dot{B}^{-\alpha +\frac{n}{p}}_{p,q}(\mathbb {R}^{n})$$ with $$1\le p<\infty $$ , $$1\le q\le \infty $$ , and analyticity of solutions for initial data $$u_{0}\in \dot{B}^{-\alpha +\frac{n}{p}}_{p,q}(\mathbb {R}^{n})$$ with $$1< p<\infty $$ , $$1\le q\le \infty $$ . Moreover the global existence and analyticity of solutions with small initial data in critical Besov spaces $$\dot{B}^{-\alpha }_{\infty ,1}(\mathbb {R}^{n})$$ is also established. In the limit case $$\alpha =1$$ , we prove global well-posedness for small initial data in critical Besov spaces $$\dot{B}^{-1+\frac{n}{p}}_{p,1}(\mathbb {R}^{n})$$ with $$1\le p<\infty $$ and $$\dot{B}^{-1}_{\infty ,1}(\mathbb {R}^{n})$$ and show analyticity of solutions for small initial data in $$\dot{B}^{-1+\frac{n}{p}}_{p,1}(\mathbb {R}^{n})$$ with $$1<p<\infty $$ and $$\dot{B}^{-1}_{\infty ,1}(\mathbb {R}^{n})$$ , respectively.
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