I am working in the area of probability theory and for a case study I would like to make some calculations in finance. Since I am developing theory for the discrete time, I am interested in models for the stock price in the discrete time. As I remember GARCH is a good one. Could you advise me something else?
It will be nice if you can tell me which model also can be used for the currency markets (since they are quite faster than the stock markets I think there should another relevant models).