Affiliation: | 1. The Nomura Centre for Mathematical Finance, Mathematical Institute, Oxford University , 24–29 St Giles, Oxford OX1 3LB, UK helen.haworth@linacre.oxon.org;3. The Nomura Centre for Mathematical Finance, Mathematical Institute, Oxford University , 24–29 St Giles, Oxford OX1 3LB, UK;4. King's College , The Strand, London WC2R 2LS, UK |