Dynamic Asset Pricing in a Unified Bachelier-Black-Scholes-Merton Model

We develop asset pricing under a unified Bachelier and Black-Scholes-Merton (BBSM) market model. We derive option pricing via the Feynman-Kac formula as well as through deflator-driven risk-neutral valuation. We show a necessary condition for the unified model to support a perpetual derivative. We develop discrete binomial pricing under the unified model. Finally, we investigate the term structure of interest rates by considering the pricing of zero-coupon bonds, forward and futures contracts. In all cases, we show that the unified model reduces to standard Black-Scholes-Merton pricing (in the appropriate parameter limit) and derive (also under the appropriate limit) pricing for a Bachelier model. The Bachelier limit of our unified model allows for positive riskless rates.