Koki Okumura
In August 2026, I will join the Department of Economics at The Chinese University of Hong Kong as an Assistant Professor.
My research interests are in macroeconomics, economic growth, and firm dynamics.
Working Papers
Inventor Mobility, Knowledge Diffusion, and Growth PDF
Abstract
We analyze the impact of inventor mobility between firms on knowledge diffusion, economic growth, and welfare. Using German patent data matched with employer-employee data, we provide evidence showing that inventor mobility between firms is associated with knowledge diffusion. Motivated by this evidence, we develop an endogenous economic growth theory in which inventors contribute to knowledge diffusion by moving between firms, in addition to engaging in internal R&D within firms. Using a model calibrated with German data, we first analyze the impact of non-compete clauses. We find that banning non-compete clauses reduces welfare by 0.38%. Furthermore, we show that optimal regulation of non-compete clauses leads to an allocation that closely approximates the social optimum and to a level of social welfare that nearly attains it. Finally, to analyze the impact of the decline in inventor mobility on economic growth over the past few decades, we calibrate the model to match the observed transition path of inventor mobility. Our results show that the decline in inventor mobility reduced growth from internal R&D by 0.04 pp and growth from knowledge diffusion by 0.20 pp, resulting in a total decrease in economic growth of 0.24 pp.
Production Networks and R&D Allocation PDF
Abstract
This paper studies how production networks shape firms’ incumbent R&D and entry incentives. We develop a dynamic model in which firms accumulate persistent buyer-supplier relationships and incumbent R&D creates new product lines that use those inherited relationships. A firm’s network affects the return to R&D through the suppliers used to produce new product lines and the buyers through which those lines generate demand. The model highlights two wedges between private and social returns: private innovators do not fully appropriate the surplus created by new product lines, and they do not internalize how product-line creation changes future matching opportunities throughout the network. We discipline the model using matched Japanese firm-to-firm transaction and patent data. In our baseline specification, the decentralized economy tilts R&D too far toward entry and young incumbent firms: the social planner reduces entry by 25.4% relative to the decentralized equilibrium, reallocates incumbent R&D toward older incumbents, and raises consumption-equivalent welfare by 1.71% along the transition.
Knowledge Creation and Diffusion with Limited Appropriation PDF
Abstract
Innovation is central to economic growth, but so is the diffusion of new knowledge. Such is the finding of recent macro papers that model the interaction between these two forces. Absent in this literature are three key elements that are the focus of this paper. First, we consider the role of frictions in matching innovators and imitators, which mediate the process of knowledge transmission. Second, we introduce the force of creative destruction, whereby innovators are replaced by imitators. Third, while most of the recent literature has focused on the case where all surplus from knowledge transmission is captured by the imitators, we consider the full range of surplus shares that the innovators and imitators can appropriate and their impact on growth. In a simple one-period model, we derive a modified Hosios condition for the optimal appropriation when firms are homogeneous. But we also find that as the degree of heterogeneity increases, the share of innovators must decrease to maximize growth. Our calibrated dynamic model suggests that the optimal share of surplus that innovators appropriate should lie in the medium range.
Dynamic Oligopoly and Innovation PDF
Abstract
We develop and estimate a tractable many-firm endogenous growth model in which firms make forward-looking R&D decisions while interacting through product-market rivalry and technology-spillover networks. The model’s linear-quadratic structure allows us to solve a dynamic oligopoly with hundreds of firms and empirically measured firm-to-firm links. Using publicly traded U.S. firms with patents, we find that competitive R&D is both underprovided in aggregate and misallocated across firms. At the observed 2017 knowledge-capital distribution, a constrained planner that reallocates R&D while holding the competitive product-market allocation fixed raises R&D to about 242% of the competitive level and consumption-equivalent welfare by 4.4%. A welfare-maximizing uniform R&D subsidy of 34% nearly replicates the constrained planner’s increase in the expected economic growth rate but raises consumption-equivalent welfare by only 0.5%. The gap reflects heterogeneous firm-level social-private R&D wedges, highlighting the limits of uniform innovation subsidies.
Ownership Structure and Economic Growth PDF
Abstract
This paper examines how the rise of common ownership affects economic growth and social welfare. We develop an endogenous growth model that incorporates three inter-firm networks: ownership, product-market rivalry, and innovation. In the model, a large number of oligopolistic firms make forward-looking R&D investment decisions, internalizing externalities on commonly owned firms arising from product-market competition and technological spillovers. We estimate the model using data on over 700 publicly traded U.S. firms with patents. Our counterfactual analysis shows that the observed increase in common ownership between 1999 and 2017 reduced the annual growth rate by 0.12 percentage points and social welfare by 0.6%. This finding suggests that, under common ownership, the internalization of the negative externality from innovation that reduces competitors’ market shares dominates the internalization of the positive externality associated with technological spillovers.