Pricing Models for FX Options
2.1 PRINCIPLES OF OPTION PRICING THEORY
We will shortly review the theory of option pricing with a strict reference to the FX world. First, we introduce a (slightly extended) BS economy, then we relax one of the basic assumptions: we will allow the volatility of the FX rate process to be stochastic. These principles will pave the way to the analysis of some well-known models employed in practice to price FX options.
2.1.1 The Black-Scholes economy
We work in continuous time and assume that Wt is a standard Brownian motion, and a martingale with respect to a filtered probability space (Ω, Ƒ, F, P ) for the time set [0, ∞). We assume also that the filtration F satisfies the usual conditions,8 and that we have a perfect frictionless market, with one domestic and foreign interest rate (at which interest accrues continuously). In the economy, one risky asset is traded: an FX pair whose price process is the following stochastic differential equation (SDE):
where µt and ςt are time-dependent parameters. A second traded asset is a riskless (domestic) deposit,9 whose price changes according to the following differential equation:
An FX pair can be considered as an asset yielding a continuous cash flow equal to the foreign interest rate. In fact, ...