# Journal of Operator Theory

Volume 79, Issue 1, Winter 2018 pp. 139-172.

Boundary representations of operator spaces, and compact rectangular matrix convex sets**Authors**: Adam H. Fuller (1), Michael Hartz (2), and Martino Lupini (3)

**Author institution:**(1) Department of Mathematics, Ohio University, Athens, OH 45701, U.S.A.

(2) Department of Mathematics, Washington University in St Louis, One Brookings Drive, St. Louis, MO 63130, U.S.A.

(3) Mathematics Department, California Institute of Technology, 1200 E. California Blvd, MC 253-37, Pasadena, CA 91125, U.S.A.

**Summary:**We initiate the study of matrix convexity for operator spaces. We define the notion of compact rectangular matrix convex set, and prove the natural analogs of the Krein--Milman and the bipolar theorems in this context. We deduce a canonical correspondence between compact rectangular matrix convex sets and operator spaces. We also introduce the notion of boundary representation for an operator space, and prove the natural analog of Arveson's conjecture: every operator space is completely normed by its boundary representations. This yields a canonical construction of the triple envelope of an operator space.

**DOI:**http://dx.doi.org/10.7900/jot.2017jan28.2165

**Keywords:**operator space, operator system, boundary representation, compact matrix convex set, matrix-gauged space

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