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Hyponormal measurable operators, affiliated to a semifinite von Neumann algebra

  • Airat Bikchentaev

摘要

Let \(\mathcal {M}\) M be a von Neumann algebra of operators on a Hilbert space \(\mathcal {H}\) H and \(\tau \) τ be a faithful normal semifinite trace on \(\mathcal {M}\) M , \(S(\mathcal {M}, \tau )\) S ( M , τ ) be the \( ^*\) -algebra of all \(\tau \) τ -measurable operators. Assume that an operator \(T\in S(\mathcal {M}, \tau )\) T S ( M , τ ) is paranormal or \( ^*\) -paranormal. If \(T^n\) T n is \(\tau \) τ -compact for some \(n\in \mathbb {N}\) n N then T is \(\tau \) τ -compact; if \(T^n=0\) T n = 0 for some \(n\in \mathbb {N}\) n N then \(T=0\) T = 0 ; if \(T^3=T\) T 3 = T then \(T=T^*\) T = T ; if \(T^2\in L_1(\mathcal {M}, \tau )\) T 2 L 1 ( M , τ ) then \(T\in L_2(\mathcal {M}, \tau )\) T L 2 ( M , τ ) and \(\Vert T\Vert _2^2=\Vert T^2\Vert _1\) T 2 2 = T 2 1 . If an operator \(T\in S(\mathcal {M}, \tau )\) T S ( M , τ ) is hyponormal and \(T^{*p}T^q\) T p T q is \(\tau \) τ -compact for some \(p, q \in \mathbb {N}\cup \{0\}\) p , q N { 0 } , \(p+q \ge 1\) p + q 1 then T is normal. If \(T\in S(\mathcal {M}, \tau )\) T S ( M , τ ) is p-hyponormal for some \(0<p\le 1\) 0 < p 1 then the operator \((T^*T)^p-(TT^*)^p\) ( T T ) p - ( T T ) p cannot have the inverse in \( \mathcal {M}\) M . If an operator \(T\in S(\mathcal {M}, \tau )\) T S ( M , τ ) is hyponormal (or cohyponormal) and the operator \(T^2\) T 2 is Hermitian then T is normal.