Title: Essays on macroeconomics
Description: This paper focuses on policies and regulations on open economies to achieve financial stability and social welfare. In the first chapter, I develop a dynamic model to study optimal liquidity regulations for multiple assets with differing levels of liquidity. I show that optimal macroprudential policies are affected by both asset liquidity and the multi-asset structure. Lower asset liquidity amplifies drops in asset prices and tightens the collateral constraint during financial crises, thus raising macroprudential taxes to discourage holding. With multiple assets, the marginal benefit of investing in one asset is affected by the future cross-price elasticities of all assets. Quantitatively, optimal macroprudential policies increases welfare by introducing a portfolio with more liquid assets and less borrowing. However, the Basel III reform deteriorates welfare, as agents overaccumulate liquid assets. In the next chapter, I focuses on the welfare analysis of currency depreciation through endogenous R&D where the economy faces a trade-off between the gain from export and disinvestment of technology.

I show that real depreciation decreases welfare when productivity is endogenous, as the long-term bust due to sluggish productivity dominates the short-term boom in consumption and output. In the final chapter, I study the optimal monetary policy in this framework. The optimal policy is a targeting rule of inflation, output gap, and the terms of trade, considering the trade-off between the international purchasing power and the cost of importing R&D. The variation of the optimal monetary policy is larger than the standard Taylor rule and the optimal monetary policy under exogenous productivity.