Non-linear characterization of Jordan $*$-isomorphisms via maps on positive cones of $C^*$-algebras

Abstract

We study maps between positive definite or positive semidefinite cones of unital $C^*$-algebras. We describe surjective maps that preserve (1) the norm of the quotient or multiplication of elements; (2) the spectrum of the quotient or multiplication of elements; (3) the spectral seminorm of the quotient or multiplication of elements. These maps relate to the Jordan $*$-isomorphisms between the specified $C^*$-algebras. While a surjection between positive definite cones that preserves the norm of the quotient of elements may not be extended to a linear map between the underlying $C^*$-algebras, the other types of surjections can be extended to a Jordan $*$-isomorphism or a Jordan $*$-isomorphism followed by the implementation by a positive invertible element. We also study conditions for the centrality of positive invertible elements. We generalize "the corollary" regarding surjections between positive semidefinite cones of unital $C^*$-algebras. Applying it, we provide positive solutions to the problem posed by Moln\'ar for general unital $C^*$-algebras.