Numeraires, equivalent martingale measures and completeness in finite dimensional securities markets

Abstract

A numeraire is a portfolio that, when securities, prices and dividends are expressed in its units, admits an equivalent martingale measure transforming any gain process into a martingale. We show that the set of equivalent martingale measures of a numeraire is one-to-one with a subset of Arrow-Debreu state prices, which becomes the whole set if and only if the numeraire is self-financing. Hence our result extends those (e.g. Harrison and Kreps (Journal of Economic Theory, 1979, 20, 381-408) Dothan (Prices in Financial Markets, Oxford Univ. Press, New York, 1990)) stated for specific self-financing numeraires. We also identify markets admitting self-financing numeraires, and characterize completeness, in terms of equivalent martingale measures, without requiring that specific securities be traded.