Product differentiation, economies of scale and entry
将规模经济引入空间竞争模型，发现新企业进入会分割需求、降低现有企业规模效率，导致社会性过度进入；即使企业可内生降低成本，进入仍过度。
This paper extends the standard circular city model of spatial competition to incorporate economies of scale. We demonstrate that new market entry generates a negative externality by fragmenting demand and forcing existing firms to operate at a less efficient scale. This scale-fragmentation channel widens the wedge between private and social entry incentives, leading to an amplified excess-entry result. When firms can endogenously invest to lower their unit costs, market entry remains socially excessive.