Refined existence theorems for doubly degenerate chemotaxis-consumption systems with large initial data

This work considers the doubly degenerate nutrient model \begin{equation*}\label{AH1} \left{ \begin{split} &u_t=\nabla\cdot\left(u^{m-1}v\nabla u\right)-\nabla\cdot\left(f(u)v\nabla v\right)+\ell uv,&&x\inΩ,,t>0, &v_t=Δv-uv, &&x\inΩ,,t>0, \end{split} \right. \end{equation*} under no-flux boundary conditions in a smoothly bounded convex domain $\mathrm{\Omega }\subset {\mathbb{R}}^n$ ($n\le 2$), where the nonnegative function $f\in C^1([0,\mathrm{\infty }))$ is assumed to satisfy $f(s)\le C_f{s}^{\alpha }$ with $\alpha >0$ and $C_f>0$ for all $s\ge 1$. When $m=2$, it was shown that a global weak solution exists, either in one-dimensional setting with $\alpha =2$, or in two-dimensional version with $\alpha \in (1,\frac{3}{2})$. The main results in this paper assert the global existence of weak solutions for $1\le m<3$ and classical solutions for $3\le m<4$ to the above system under the assumption \begin{equation*} α\in \left{ \begin{split} &\left[m-1,\min\left{m,\frac{m}{2}+1\right}\right]~~&&$\text{if}$n=1,\quad\quad$\text{and}$ &\left(m-1,\min\left{m,\frac{m}{2}+1\right}\right)&&$\text{if}$~~n=2, \end{split} \right. \end{equation*} which extend the range $\alpha \in (1,\frac{3}{2})$ to $\alpha \in (1,2)$ in two dimensions for the case $m=2$. Our proof will be based on a new observation on the coupled energy-type functional and on an inequality with general form.