Operator Kantorovich inequality for 2-positive linear maps

From papers

Let 0<mAM0<m\le A\le M, and let X,YX,Y be partial isometries on a Hilbert space H\mathcal{H} whose final spaces are orthogonal to each other. Let Φ\Phi be a 22-positive linear map. Operator Kantorovich inequality. Then

\left\\|\Phi(X^*AY)\Phi(Y^*AY)^{-1}\Phi(Y^*AX)\Phi(X^*AX)^{-1}\right\\|\le \left(\frac{M-m}{M+m}\right)^2.

This assertion is motivated by the operator Wielandt inequality and related Schwarz inequalities for 22-positive maps. The authors state that they have been unable to prove or disprove it, so its status remains open.

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Primary source

Minghua Lin, “On an operator Kantorovich inequality for positive linear maps”, arXiv:1212.5690 (2012).

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