On the Chordal Transform of Hilbert Space Operators

Abstract

Let B(H) denote the C*-algebra of all bounded linear operators on a separable Hilbert space H. For A,B∈B(H), the chordal transform f_(A,B), as an operator on B(H), is defined by {f_(A,B)(X)=(\vert A^*\vert ^2+I)^(-1/2){\delta_(A,B)(X)(\vert B\vert ^2+I)^(-1/2)}, where {\delta_(A,B)} is the generalized derivation defined on B(H) by {\delta _(A,B)(X)=AX-XB}. Orthogonality of the range and the kernel of f_(A,B), with respect to the unitarily invariant norms \vert \vert \vert .\vert \vert \vert , are discussed. It is shown that if A, B are self-adjoint, then {\vert \vert \vert f_(A,B)(X)\vert \vert \vert \le \vert \vert \vert X\vert \vert \vert for all X. Related norm inequalities comparing f_(A,B) and {\delta _(A,B) are also given.