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Working Paper
Collateralized Debt Networks with Lender Default
The Lehman Brothers' 2008 bankruptcy spread losses to its counterparties even when Lehman was a lender of cash, because collateral for that lending was tied up in the bankruptcy process. I study the implications of such lender default using a general equilibrium network model featuring endogenous leverage, endogenous asset prices, and endogenous network formation. The multiplex graph model has two channels of contagion: a counterparty channel of contagion and a price channel of contagion through endogenous collateral price. Borrowers diversify their lenders because of the counterparty risk, ...
Working Paper
The Economics of Platforms in a Walrasian Framework
We present a tractable model of platform competition in a general equilibrium setting. We endogenize the size, number, and type of each platform, while allowing for different user types in utility and impact on platform costs. The economy is Pareto effcient because platforms internalize the network effects of adding more or different types of users by offering type-specific contracts that state both the number and composition of platform users. Using the Walrasian equilibrium concept, the sum of type-specific fees paid cover platform costs. Given the Pareto efficiency of our environment, we ...
Working Paper
On Default and Uniqueness of Monetary Equilibria
We examine the role that credit risk in the central bank's monetary operations plays in the determination of the equilibrium price level and allocations. Our model features trade in fiat money, real assets and a monetary authority which injects money into the economy through short-term and long-term loans to agents. Short-term loans are riskless, but long-term loans are collateralized by a portfolio of real assets and are subject to credit risk. The private monetary wealth of individuals is zero, i.e., there is no outside money. When there is no default in equilibrium, there is indeterminacy. ...
Report
Paradoxes and Problems in the Causal Interpretation of Equilibrium Economics
Equilibrium assumptions posit relations between different people's beliefs and behavior without describing a process that causes these relations to hold. I show that because equilibrium models do not describe a causal process whereby one endogenous variable affects another, attempts to decompose the effects of shocks into “direct” and “indirect” effects can suggest misleading predictions about how these models work. Equilibrium assumptions also imply absurd paradoxes: history can determine future behavior without affecting any intervening state variables today; individuals can learn ...
Working Paper
Optimal Epidemic Control in Equilibrium with Imperfect Testing and Enforcement
We analyze equilibrium behavior and optimal policy within a Susceptible-Infected-Recovered epidemic model augmented with potentially undiagnosed agents who infer their health status and a social planner with imperfect enforcement of social distancing. We define and prove the existence of a perfect Bayesian Markov competitive equilibrium and contrast it with the efficient allocation subject to the same informational constraints. We identify two externalities, static (individual actions affect current risk of infection) and dynamic (individual actions affect future disease prevalence), and ...