Can Negative Interest Rates Really Affect Option Pricing? Empirical Evidence from an Explicitly Solvable Stochastic Volatility Model

The profound financial crisis generated by the collapse of Lehman Brothers and the European sovereign debt crisis in 2011 have caused negative values of government bond yields both in the U.S.A. and in the EURO area. This paper investigates whether the use of models which allow for negative interest rate can improve option pricing and implied volatility forecasting. This is done with special attention to Foreign eXchange and index options. To this end, we carried out an empirical analysis of the prices of call and put options on the U.S. S&P 500 index as well as on the Eurodollar futures using a generalization of the Heston model in the stochastic interest rate framework. Specifically, the dynamics of the option's underlying asset is described by two factors: a stochastic variance and a stochastic interest rate. The volatility is not allowed to be negative while the interest rate is. Explicit formulas for the transition probability density function and moments are derived. These formulas are used to efficiently estimate the model parameters. Three empirical analyses are illustrated. The first two show that the use of models which allow for negative interest rates can efficiently reproduce implied volatility and forecast option prices (i.e. S&P index and foreign exchange options). The last one studies how the U.S. three month government bond yield affects the U.S. S&P 500 index