Properties of given and detected unbounded solutions to a class of chemotaxis models.

This paper deals with unbounded solutions to a class of chemotaxis systems. In particular, for a rather general attraction–repulsion model, with nonlinear productions, diffusion, sensitivities, and logistic term, we detect Lebesgue spaces where given unbounded solutions also blow up in the corresponding norms of those spaces; subsequently, estimates for the blow‐up time are established. Finally, for a simplified version of the model, some blow‐up criteria are proved. More precisely, we analyze a zero‐flux chemotaxis system essentially described as ⋄ut=∇·((u+1)m1−1∇u−χu(u+1)m2−1∇v+ξu(u+1)m3−1∇w)+λu−μukinΩ×(0,Tmax),0=Δv−1|Ω|∫Ωuα+uα=Δw−1|Ω|∫Ωuβ+uβinΩ×(0,Tmax).$$\begin{equation} {\begin{cases} u_t= \nabla \cdot ((u+1)^{m_1-1}\nabla u -\chi u(u+1)^{m_2-1}\nabla v & {}\\ \qquad +\; \xi u(u+1)^{m_3-1}\nabla w) +\lambda u -\mu u^k & \text{ in } \Omega \times (0,T_{max}),\\ 0= \Delta v -\frac{1}{\vert {\Omega }\vert }\int _\Omega u^\alpha + u^\alpha = \Delta w - \frac{1}{\vert {\Omega }\vert }\int _\Omega u^\beta + u^\beta & \text{ in } \Omega \times (0,T_{max}). \end{cases}} \end{equation}$$The problem is formulated in a bounded and smooth domain Ω of Rn$\mathbb {R}^n$, with n≥1$n\ge 1$, for some m1,m2,m3∈R$m_1,m_2,m_3\in \mathbb {R}$, χ,ξ,α,β,λ,μ>0$\chi , \xi , \alpha ,\beta , \lambda ,\mu >0$, k>1$k >1$, and with Tmax∈(0,∞]$T_{max}\in (0,\infty ]$. A sufficiently regular initial data u0≥0$u_0\ge 0$ is also fixed. Under specific relations involving the above parameters, one of these always requiring some largeness conditions on m2+α$m_2+\alpha$, (i)we prove that any given solution to (⋄$\Diamond$), blowing up at some finite time Tmax$T_{max}$ becomes also unbounded in Lp(Ω)$L^{\mathfrak {p}}(\Omega)$‐norm, for all p>n2(m2−m1+α)${\mathfrak {p}}>\frac{n}{2}(m_2-m_1+\alpha)$;(ii)we give lower bounds T (depending on ∫Ωu0p¯$\int _\Omega u_0^{\bar{p}}$) of Tmax$T_{max}$ for the aforementioned solutions in some Lp¯(Ω)$L^{\bar{p}}(\Omega)$‐norm, being p¯=p¯(n,m1,m2,m3,α,β)≥p$\bar{p}=\bar{p}(n,m_1,m_2,m_3,\alpha ,\beta)\ge \mathfrak {p}$;(iii)whenever m2=m3$m_2=m_3$, we establish sufficient conditions on the parameters ensuring that for some u0 solutions to (⋄$\Diamond$) effectively are unbounded at some finite time. Within the context of blow‐up phenomena connected to problem (⋄$\Diamond$), this research partially improves the analysis in Wang et al. (J Math Anal Appl. 2023;518(1):126679) and, moreover, contributes to enrich the level of knowledge on the topic. [ABSTRACT FROM AUTHOR]