We consider the following attraction–repulsion Keller–Segel system:
with homogeneous Neumann boundary conditions in a bounded domain 惟⊂R2 with smooth boundary. The system models the chemotactic interactions between one species (denoted by u) and two competing chemicals (denoted by v and w), which has important applications in Alzheimer's disease. Here all parameters 蠂, 尉, 伪, 尾, 纬 and 未 are positive. By constructing a Lyapunov functional, we establish the global existence of uniformly-in-time bounded classical solutions with large initial data if the repulsion dominates or cancels attraction (i.e., 尉纬≥伪蠂). If the attraction dominates (i.e., 尉纬<伪蠂), a critical mass phenomenon is found. Specifically speaking, we find a critical mass such that the solution exists globally with uniform-in-time bound if M<m鈦?/sub> and blows up if cdf10193e2fb3947eadf1d37b37011" title="Click to view the MathML source">M>m鈦?/sub> and where N+ denotes the set of positive integers and M=∫惟u0dx the initial cell mass.