Risky Arbitage, Asset Prices, and Externalities

Abstract

We introduce a no-risky-arbitrage price (NRAP) condition for asset market models allowing both unbounded short sales and externalities such as trading volume. We then demonstrate that the NRAP condition is sufficient for the existence of competitive equilibrium in the presence of externalities. Moreover, we show that if all risky arbitrages are utility increasing, then the NRAP condition characterizes competitive equilibrium in the presence of externalities.