English

Bicommutants and ranges of derivations

Rings and Algebras 2013-06-11 v2 Functional Analysis Operator Algebras

Abstract

Let VV be a vector space over a field FF, VV^* its dual space and L(V)L(V) the algebra of all linear operators on VV. For an operator aL(V)a\in L(V) let aa* be its adjoint acting on VV*, and for a subset RR of L(V)L(V) let R"R" be its bicommutant. If RR is the subalgebra of L(V)L(V) generated by an operator aa, we prove that the set Z:=b:bR"Z:={b*: b\in R}" is contained in b:bR"{b*: b\in R"}; moreover ZZ is described. This inclusion is equality if VV as a module over the polynomial algebra R=F[t]R=F[t] via tat\mapsto a is nice enough (say torsion, or injective, or if it contains a copy of RR as a direct summand). Further, under the same assumption about VV for any bL(V)b\in L(V), b(a)"b\in(a)" if and only if the derivations dad_a and dbd_b satisfy db(F(V))da(F(V))d_b(F(V))\subseteq d_a(F(V)), where F(V)F(V) is the set of all finite rank operators on VV. The inclusion db(L(V))da(L(V))d_b(L(V))\subseteq d_a(L(V)) also holds under these conditions.

Keywords

Cite

@article{arxiv.1208.3941,
  title  = {Bicommutants and ranges of derivations},
  author = {Bojan Magajna},
  journal= {arXiv preprint arXiv:1208.3941},
  year   = {2013}
}

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20 pages