Product of Operators and Numerical Range Preserving Maps
نویسندگان
چکیده
Let V be the C∗-algebra B(H) of bounded linear operators acting on the Hilbert space H, or the Jordan algebra S(H) of self-adjoint operators in B(H). For a fixed sequence (i1, . . . , im) with i1, . . . , im ∈ {1, . . . , k}, define a product of A1, . . . , Ak ∈ V by A1 ∗ · · · ∗ Ak = Ai1 . . . Aim . This includes the usual product A1 ∗ · · · ∗ Ak = A1 · · ·Ak and the Jordan triple product A ∗ B = ABA as special cases. Denote the numerical range of A ∈ V by W (A) = {(Ax, x) : x ∈ H, (x, x) = 1}. If there is a unitary operator U and a scalar μ satisfying μ = 1 such that φ : V→ V has the form A 7→ μU∗AU or A 7→ μU∗AtU, then φ is surjective and satisfies W (A1 ∗ · · · ∗ Ak) =W (φ(A1) ∗ · · · ∗ φ(Ak)) for all A1, . . . , Ak ∈ V. It is shown that the converse is true under the assumption that one of the terms in (i1, . . . , im) is different from all other terms. In the finite dimensional case, the converse can be proved without the surjective assumption on φ. An example is given to show that the assumption on (i1, . . . , im) is necessary. 2000 Mathematics Subject Classification. 47A12, 47B15, 47B49, 15A60, 15A04, 15A18
منابع مشابه
On strongly Jordan zero-product preserving maps
In this paper, we give a characterization of strongly Jordan zero-product preserving maps on normed algebras as a generalization of Jordan zero-product preserving maps. In this direction, we give some illustrative examples to show that the notions of strongly zero-product preserving maps and strongly Jordan zero-product preserving maps are completely different. Also, we prove that the direct p...
متن کاملThe second dual of strongly zero-product preserving maps
The notion of strongly Lie zero-product preserving maps on normed algebras as a generalization of Lie zero-product preserving maps are dened. We give a necessary and sufficient condition from which a linear map between normed algebras to be strongly Lie zero-product preserving. Also some hereditary properties of strongly Lie zero-product preserving maps are presented. Finally the second dual of...
متن کاملAdditive Maps Preserving Idempotency of Products or Jordan Products of Operators
Let $mathcal{H}$ and $mathcal{K}$ be infinite dimensional Hilbert spaces, while $mathcal{B(H)}$ and $mathcal{B(K)}$ denote the algebras of all linear bounded operators on $mathcal{H}$ and $mathcal{K}$, respectively. We characterize the forms of additive mappings from $mathcal{B(H)}$ into $mathcal{B(K)}$ that preserve the nonzero idempotency of either Jordan products of operators or usual produc...
متن کاملMaps preserving the joint numerical radius distance of operators
Denote the joint numerical radius of an m-tuple of bounded operators A = (A1, . . . , Am) by w(A). We give a complete description of maps f satisfying w(A − B) = w(f(A) − f(B)) for any two m-tuples of operators A = (A1, . . . , Am) and B = (B1, . . . , Bm). We also characterize linear isometries for the joint numerical radius, and maps preserving the joint numerical range of A. AMS Classificati...
متن کاملOn Preserving Properties of Linear Maps on $C^{*}$-algebras
Let $A$ and $B$ be two unital $C^{*}$-algebras and $varphi:A rightarrow B$ be a linear map. In this paper, we investigate the structure of linear maps between two $C^{*}$-algebras that preserve a certain property or relation. In particular, we show that if $varphi$ is unital, $B$ is commutative and $V(varphi(a)^{*}varphi(b))subseteq V(a^{*}b)$ for all $a,bin A$, then $varphi$ is a $*$-homomorph...
متن کاملShift Invariant Spaces and Shift Preserving Operators on Locally Compact Abelian Groups
We investigate shift invariant subspaces of $L^2(G)$, where $G$ is a locally compact abelian group. We show that every shift invariant space can be decomposed as an orthogonal sum of spaces each of which is generated by a single function whose shifts form a Parseval frame. For a second countable locally compact abelian group $G$ we prove a useful Hilbert space isomorphism, introduce range funct...
متن کامل