Risk managing bermudan swaptions in the libor BGM model

Abstract

This article presents a novel approach for calculating swap vegaper bucket in the Libor BGM model. We show that for some forms of thevolatility an approach based on re-calibration may lead to a large uncertaintyin estimated swap vega, as the instantaneous volatility structure maybe distorted by re-calibration. This does not happen in the case of constantswap rate volatility. We then derive an alternative approach, not based onre-calibration, by comparison with the swap market model. The strength ofthe method is that it accurately estimates vegas for any volatility functionand at a low number of simulation paths. The key to the method is thatthe perturbation in the Libor volatility is distributed in a clear, stable andwell understood fashion, whereas in the re-calibration method the change involatility is hidden and potentially unstable.risk management;libor BGM model;central interest rate model;bermudan swaptions;swap market model