Author's School

Graduate School of Arts & Sciences

Author's Department/Program



English (en)

Date of Award

January 2011

Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Rodolfo Manuelli


The scope of the dissertation is: broadly-defined) general macroeconomics. The first essay is on optimal taxation and capital structure, the second essay is on firm dynamics, and the third essay is on financial crises. The first essay clarifies the role of the corporate income tax: as a form of double taxation) for achieving socially optimal allocations in the Mirrlees framework when the government cannot tax unrealized capital income at the individual level. Use of the corporate tax requires changes in the individual capital tax. The novelty of the paper is that the sophisticated tax system is designed to influence the individual agent's portfolio choice of debt and equity, which in turn endogenizes the leverage ratio. The optimum corporate tax is indeterminate, but a minimal level is ecessary. An immediate question is what happens to capital structure if we increase or decrease the level of the corporate tax. Surprisingly, unlike in classical capital structure theories, in this optimal tax mechanism, the firm's leverage ratio is independent of the corporate tax rate. The second essay examines firm dynamics to explain the following empirical facts:: i) The size of a firm and its growth rate are negatively correlated;: ii) but, they are often independent for firms above a certain size. Existing theories of firm dynamics can explain the first fact, but cannot explain the second. This paper studies a dynamic moral hazard problem under an AK-technology. In a first best world, the expected growth rate is strictly decreasing with capital. However, with information asymmetry our theory is consistent with both empirical facts because the optimal contract dictates under-investment in low-level capital states and over-investment in high-level capital states. The reason is that the given convex production technology becomes nonconvex in equilibrium due to the information asymmetry and the degree of the nonconvexity differs by the level of capital. We also fully characterize the agent's incentives. The capital accumulation mechanism induces incentive schemes that are different from optimal contracts in the literature on principal-agent models. Finally, in the third essay - This essay is a joint work with Costas Azariadis - we propose a model of financial crises as transitions from an efficient and unstable state to an inefficient and stable state in a simple economy with sector-specific shocks. The main driving force of this transition is the unwinding of unsecured loans. Introducing public debt increases the volatility of stock prices. We also discuss possible policy interventions.


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