Abstract:
We study transitivity conditions on the norm of JB *-triples, C *-algebras, JB-algebras, and their preduals. We show that, for the predual X of a JBW *-triple, each one of the following conditions i) and ii) implies that X is a Hilbert space. i) The closed unit ball of X has some extreme point and the norm of X is convex transitive. ii) The set of all extreme points of the closed unit ball of X is non rare in the unit sphere of X. These results are applied to obtain partial affirmative answers to the open problem whether every JB *-triple with transitive norm is a Hilbert space. We extend to arbitrary C *-algebras previously known characterizations of transitivity [20] and convex transitivity [36] of the norm on commutative C *-algebras. Moreover, we prove that the Calkin algebra has convex transitive norm. We also prove that, if X is a JB-algebra, and if either the norm of X is convex transitive or X has a predual with convex transitive norm, then X is associative. As a consequence, a JB-algebra with almost transitive norm is isomorphic to the field of real numbers.
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Received: 9 June 1999 / Revised version: 20 February 2000
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Becerra Guerrero, J., Rodriguez Palacios, A. Transitivity of the norm on Banach spaces¶ having a Jordan structure. manuscripta math. 102, 111–127 (2000). https://doi.org/10.1007/s002291020111
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DOI: https://doi.org/10.1007/s002291020111