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We study the dynamic Ramsey problem of finding optimal public debt and linear taxes on capital and labor income within a tractable infinite horizon model with incomplete markets. With zero public expenditure and debt, it is optimal to tax the risky labor income and subsidize capital, while a positive amount of public debt is welfare improving. A steady state optimality condition is derived which implies that the tax on capital is positive, when savings are sufficiently inelastic to returns. A calibration of our model to the US economy indicates positive optimal taxes and a small but positive optimal debt level.

When individuals' labor and capital income are subject to uninsurable idiosyncratic risks, should capital and labor be taxed, and if so how? In a two-period general equilibrium model with production, we derive a decomposition formula of the welfare effects of these taxes into insurance and distribution effects. This allows us to determine how the sign of the optimal taxes on capital and labor depend on the nature of the shocks and the degree of heterogeneity among consumers' income, as well as on the way in which the tax revenue is used to provide lump-sum transfers to consumers. When shocks affect primarily labor income and heterogeneity is small, the optimal tax on capital is positive. However, in other cases a negative tax on capital is welfare-improving.

In the context of an epidemic, a society is forced to face a system of externalities in consumption and in production. Command economy interventions can support efficient allocations at the cost of severe information requirements. Competitive markets for infection rights (alternatively, Pigouvian taxes) can guarantee efficiency without requiring direct policy interventions on socio-economic activities. We demonstrate that this is the case also with moral hazard, when the infections cannot be associated to the specific activities which originated them. Finally, we extend the analysis to situations where governments have only incomplete information regarding the values of the parameters of the infection or of firms' production.

In this article we examine the competitive equilibria of a dynamic stochastic economy with complete markets and collateral constraints. We show that, provided the sets of asset pay-offs and of collateral levels are sufficiently rich, the equilibrium allocations with sequential trades and collateral constraints are equivalent to those obtained in Arrow-Debreu markets subject to a series of limited pledgeability constraints. We provide both necessary and sufficient conditions for equilibria to be Pareto efficient and show that when collateral is scarce equilibria are not only Pareto inefficient but also often constrained inefficient, in the sense that imposing tighter borrowing restrictions can make everybody in the economy better off. We derive sufficient conditions for the existence of Markov equilibria and, for the case of two agents, for the existence of equilibria that have finite support. These equilibria can be computed with arbitrary accuracy and the model is very tractable.

In many countries, lenders are not permitted to use information about past defaults after a specified period of time has elapsed. We model this provision and determine conditions under which it is optimal. We develop a model in which entrepreneurs must repeatedly seek external funds to finance a sequence of risky projects under conditions of both adverse selection and moral hazard. Forgetting a default typically makes incentives worse, ex-ante, because it reduces the punishment for failure. However, following a default it may be good to forget, because by improving an entrepreneur's reputation, forgetting increases the incentive to exert effort to preserve this reputation. Our key result is that if (i) borrowers' incentives are sufficiently strong, (ii) their average quality is not too low, (iii) the output loss from low effort is not too large, and (iv) agents are sufficiently patient, then the optimal law would prescribe some amount of forgetting that is, it would not permit lenders to fully utilize past information. We also argue that forgetting must be the outcome of a regulatory intervention by the government no lender would willingly agree to ignore information available to him. Finally, we show that the predictions of our model are consistent with the cross-country relationship between credit bureau reporting regulations and the provision of credit, as well as Musto (2004)'s evidence on the impact of these regulations on individual borrower and lender behavior.

In many countries, lenders are restricted in their access to information about borrowers' past defaults. We study this provision in a model of repeated borrowing and lending with moral hazard and adverse selection. We analyze its effects on borrowers' incentives and access to credit, and identify conditions under which it is optimal. We argue that "forgetting" must be the outcome of a regulatory intervention by the government. Our model's predictions are consistent with the cross-country relationship between credit bureau regulations and provision of credit, as well as the evidence on the impact of these regulations on borrowers' and lenders' behavior.