Dynamics of Markups, Concentration and Product Span
构建了一个包含多产品企业与单产品企业的模型，研究产品创新如何导致加成率和集中度上升、劳动份额下降，并发现劳动生产率与产品范围之间可能存在倒U型关系。
We develop a model with a finite number of multiproduct firms together with a continuum of single-product firms and study the dynamics that arise from product innovation. Consistent with the available evidence, the model predicts rising markups and concentration and a declining labor share. Our dynamics predict the possibility of an inverted-U relationship between labor productivity and product span, for which we provide suggestive evidence. In the optimal allocation, product span and labor productivity are strictly positively related. We also characterize optimal policies for these types of sectors.