The term structure of interest rates in a heterogeneous monetary union

We build an arbitrage-based model of the yield curves in a heterogeneous monetary union with sovereign default risk, which can account for the asymmetric shifts in euro area yields during the Covid-19 pandemic. We derive an affine term structure solution and decompose yields into term premium and credit risk components. In an extension, we endogenize the peripheral default probability, showing that it decreases with central bank bond holdings. Calibrating the model to Germany and Italy, we show that a 'default risk extraction' channel is the main driver of Italian yields and that flexibility makes asset purchases more effective.