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On the martingale property of stochastic exponentials

Published online by Cambridge University Press:  14 July 2016

Bernard Wong*
Affiliation:
University of New South Wales and Australian National University
C. C. Heyde*
Affiliation:
Australian National University and Columbia University
*
Postal address: School of Actuarial Studies, University of New South Wales, Sydney, NSW 2052, Australia. Email address: [email protected]
∗∗ Postal address: Mathematical Sciences Institute, Australian National University, Canberra, ACT 0200, Australia

Abstract

We present a necessary and sufficient condition for a stochastic exponential to be a true martingale. It is proved that the criteria for the true martingale property are related to whether a related process explodes. An alternative and interesting interpretation of this result is that the stochastic exponential is a true martingale if and only if under a ‘candidate measure’ the integrand process is square integrable over time. Applications of our theorem to problems arising in mathematical finance are also given.

Type
Research Papers
Copyright
Copyright © Applied Probability Trust 2004 

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