Let X be an operator space, let phi be a product on X, and let (X, V) denote the algebra that one obtains. We give necessary and sufficient conditions on the bilinear mapping V for the algebra (X, phi) to have a completely isometric representation as an algebra of operators on some Hilbert space. In particular, we give an elegant geometrical characterization of such products by using the Haagerup tensor product. Our result makes no assumptions about identities or approximate identities. Our proof is independent of the earlier result of Blecher, Ruan and Sinclair [D.P. Blecher, Z.-J. Ruan, A.M. Sinclair, A characterization of operator algebras. J. Funct. Anal. 89 (1) (1990) 188-201] which solved the case when the bilinear mapping has an identity of norm one, and our result is used to give a simple direct proof of this earlier result. We also develop further the connections between quasi -multipliers of operator spaces and their representations on a Hilbert space or their embeddings in the second dual, and show that the quasi -multipliers of operator spaces defined in [M. Kaneda, V.I. Paulsen, Quasi-multipliers of operator spaces, J. Funct. Anal. 217 (2) (2004) 347-365] coincide with their C*-algebraic counterparts. (c) 2007 Elsevier Inc. All rights reserved.
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