We investigate financial markets under model risk caused by uncertain volatilities. For this purpose we consider a financial market that features volatility uncertainty. To have a mathematical consistent framework we use the notion of G-expectation and its corresponding G-Brownian motion...

Based on criteria of mathematical simplicity and consistency with empirical market data, a stochastic volatility model is constructed, the volatility process being driven by fractional noise. Price return statistics and asymptotic behavior are derived from the model and compared with data....

In this paper, we reexamine and extend the stochastic volatility model of Stein and Stein (1991) where volatility follows a mean-reversion Ornstein-Uhlenbeck process. Using Fourier inversion techniques we are able to allow for correlation between instan-taneous volatilities and the underlying...