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Best possibility of the Furuta inequality
Authors:  tarô   Tanahashi
Affiliation:Department of Mathematics, Tohoku College of Pharmacy, Komatsushima, Aoba-ku, Sendai 981, Japan
Abstract:
Let $0le p,q,rinmathbb R, p+2rle(1+2r)q$, and $1le q$. Furuta (1987) proved that if bounded linear operators $A,Bin B(H)$ on a Hilbert space $H$ $(dim(H)ge 2)$ satisfy $0le Ble A$, then $(A^r B^p A^r)^{1/q} le A^{(p+2r)/q}$. In this paper, we prove that the range $p+2rle (1+2r)q$ and $1le q$ is best possible with respect to the Furuta inequality, that is, if $(1+2r) q<p+2r$ or $0<q<1$, then there exist $A,Bin B(mathbb R^2)$ which satisfy $0le Ble A$ but $(A^r B^p A^r)^{1/q}nleq A^{(p+2r)/q}$.

Keywords:The L"  owner-Heinz inequality, the Furuta inequality, positive operator
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