A defaultable HJM modelling of the Libor rate for pricing Basis Swaps after the credit crunch

• The Libor rate is considered as a risky rate.
• We define a credit spread through the implied default intensity of the Libor banks.
• We use a defaultable HJM methodology to model the term structure of credit spreads.
• We estimate the spread of a Basis Swap by using a numerical method.
• Numerical results are accurate and in line with the real market values.

A great deal of recent literature discusses the major anomalies that have appeared in the interest rate market following the credit crunch in August 2007. There were major consequences with regard to the development of spreads between quantities that had remained the same until then. In particular, we consider the spread that opened up between the Libor rate and the OIS rate, and the consequent empirical evidence that FRA rates can no longer be replicated using Libor spot rates due to the presence of a Basis spread between floating legs of different tenors. We develop a credit risk model for pricing Basis Swaps in a multi-curve setup. The Libor rate is considered here as a risky rate, subject to the credit risk of a generic counterparty whose credit quality is refreshed at each fixing date. A defaultable HJM methodology is used to model the term structure of the credit spread, defined through the implied default intensity of the contributing banks of the Libor corresponding to a chosen tenor. A forward credit spread volatility function depending on the entire credit spread term structure is assumed. In this context, we implement the model and obtain the price of Basis Swaps using a numerical scheme based on the Euler–Maruyama stochastic integral approximation and the Monte Carlo method.