We show that there are two distinct ways to make volatility stochastic that are differentiated by their consequences for skewness. Most models in the literature have adopted the relatively tractable methodology of using stochastic time changes to engineer stochastic volatility. Unfortunately,...

The martingale theory of price bubbles defines an asset bubble to exist when the asset's price process is a strict local martingale, that is, a local martingale that is not a martingale. Using this definition of a price bubble, for continuous semimartingales, we characterize the conditions under...