2015/12/20 by Boedihardjo, March, Dykema, Ken
#46L54 #FOS: Mathematics #Operator Algebras (math.OA)
paper · doi:10.48550/arxiv.1512.06321
For an element in an algebra-valued *-noncommutative probability space, equivalent conditions for algebra-valued R-diagonality (a notion introduced by Sniady and Speicher) are proved. Formal power series relations involving the moments and cumulants of such R-diagonal elements are proved. Decompositions of algebra-valued R-diagonal elements into products of the form unitary times self-adjoint are investigated; sufficient conditions, in terms of cumulants, for *-freeness of the unitary and the self-adjoint part are proved, and a tracial example is given where *-freeness fails. The particular case of algebra-valued circular elements is considered; as an application, the polar decompostion of the quasinilpotent DT-operator is described. An erratum is appended. (The last sentence in the above paragraph is thereby nullified.)