The Robustness of n(s) <~ 0.95 in racetrack inflation

A spectral index ns . 0.95 appears to be a generic prediction of racetrack inflation models. Reducing a general racetrack model to a single-field inflation model with a simple potential, we obtain an analytic expression for the spectral index, which explains this result. By considering the limits of validity of the derivation, possible ways to achieve higher values of the spectral index are described, although these require further fine-tuning of the potential. DESY 07-210, LPT-ORSAY-07-124