Ambiguity, Nominal Bond Yields, and Real Bond Yields

This paper presents an equilibrium bond-pricing model that jointly explains the upward-sloping nominal and real yield curves and the violation of the expectations hypothesis. Instead of relying on the inflation risk premium, the ambiguity-averse agent faces different amounts of Knightian uncertainty in the long run versus the short run; hence, the model-implied nominal and real short rate expectations are upward sloping under the agent's worst-case equilibrium beliefs. The expectations hypothesis roughly holds under investors' worst-case beliefs. The difference between the worst-case scenario and the true distribution makes realized excess returns on long-term bonds predictable.