Published online by Cambridge University Press: 06 April 2009
This paper develops the parametric restrictions imposed on diffusion state processes by the requirement of arbitrage-free asset pricing. Using the equivalent martingale measure as a starting point, the diffusion property is exploited to specify the shadow pricing function, which takes conditional state variable probabilities under the reference measure into arbitrage-free contingent claim prices. The main results of the paper provide differential equations associated with the shadow price function that are used to identify restrictions on the parameters of assumed diffusion processes. The paper concludes with an application to the CIR model where the state variable, the instantaneous interest rate, is assumed to follow a square root process. Calculations are also provided for the parametric restrictions imposed on the Brownian bridge and OU state variable processes.