the NAPA Conference on Financial Markets Research, and the European Finance Association for their suggestions. We thank Kevin Crotty and Juan Mendez for research assistance. This paper was prepared for the Brookings Papers on Economic Activity Fall 2011 issue. We have received an honorarium for the presentation of the paper at Brookings. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. At least one co-author has disclosed a financial relationship of potential relevance for this research. Further information is available online at http://www.nber.org/papers/w17555.ack NBER working papers are circulated for discussion and comment purposes. They have not been peerreviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.

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We model the dynamics of risk premia during crises in asset markets where the marginal investor is a financial intermediary. Intermediaries face an equity capital constraint. Risk premia rise when the constraint binds, reflecting the capital scarcity. The calibrated model matches the nonlinearity of risk premia during crises and the speed of reversion in risk premia from a crisis back to precrisis levels. We evaluate the effect of three government policies: reducing intermediaries borrowing costs, injecting equity capital, and purchasing distressed assets. Injecting equity capital is particularly effective because it alleviates the equity capital constraint that drives the model's crisis. (JEL E44, G12, G21, G23, G24)

We present a model of optimal intervention in a flight to quality episode. JEL Codes: E30, E44, E5, F34, Gl, G21, G22, G28.

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