The literature on leverage until now shows how an increase in volatility reduces leverage. However, in order to explain pro-cyclical leverage it assumes that bad news increases volatility. This paper suggests a reason why bad news is more often than not associated with higher future volatility. We show that, in a model with endogenous leverage and heterogeneous beliefs, agents have the incentive to invest mostly in technologies that become volatile in bad times. Together with the old literature this explains pro-cyclical leverage. The result also gives rationale to the pattern of volatility smiles observed in the stock options since 1987. Finally, the paper presents for the ﬁrst time a dynamic model in which an asset is endogenously traded simultaneously at diﬀerent margin requirements in equilibrium.
Fostel, Ana and Geanakoplos, John, "Why Does Bad News Increase Volatility and Decrease Leverage?" (2010). Cowles Foundation Discussion Papers. 2095.