We propose a flexible and tractable approach based on affine processes to model multiple yield curves. More precisely, we model a numeraire process and multiplicative spreads between Libor rates and simply compounded OIS rates as functions of an underlying affine process. Besides allowing for ordered spreads and an exact fit to the initially observed term structures, this general framework leads to tractable valuation formulas for caplets and swaptions and embeds most of the existing multi-curve models based on affine processes. In particular, in the case of a model driven by a Wishart process, we derive a closed-form pricing formula for caplets. The empirical performance of some specifications of our framework is illustrated by calibration to market data.
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