Essays on macroeconomic theory

This dissertation collects three studies on macroeconomic theory and consists of four chapters. The first chapter is the introduction.; In Chapter 2, I study economic growth and catch-up using a multi-country model in which sustained economic growth occurs due to learning-by-doing and invention, and in which countries interact through international trade. I consider how catch-up occurs in such an environment. The main finding is that in the three-country version of the model the middle-income country tends to grow fastest. Empirical relevance of this finding is also discussed.; Chapter 3 is a study on business cycles. I aim there to show demand shocks can replicate important aspects of business cycles at least as well as the real business cycle theory does. A key feature of the model is that capital utilization rate can vary according to demand shocks. It generates procyclical variation in the Solow residual and enables the model to reproduce the second moments of major macroeconomic variables. As a microeconomic foundation of demand shocks, I provide how incomplete market economies can be aggregated into representative agent economies with preference shocks.; Finally, in Chapter 4, I aim to extend the dynamic programming theory to the case in which the return function is not bounded and the state variables may grow unboundedly. The main contribution is a new way to prove the uniqueness of the value function and the convergence of the Bellman iteration.