Asymmetric Choi--Davis inequalities

Abstract

Let $\Phi$ be a unital positive linear map and let $A$ be a positive invertible operator. We prove that there exist partial isometries $U$ and $V$ such that \[ |Φ(f(A))Φ(A)Φ(g(A))|\leq U^*Φ(f(A)Ag(A))U \] and \[\left|Φ\left(f(A)\right)^{-r}Φ(A)^rΦ\left(g(A)\right)^{-r}\right|\leq V^*Φ\left(f(A)^{-r}A^rg(A)^{-r}\right)V\] hold under some mild operator convex conditions and some positive numbers $r$. Further, we show that if $f^2$ is operator concave, then $$|\Phi (f(A))\Phi (A)|\le \Phi (Af(A)).$$ In addition, we give some counterparts to the asymmetric Choi--Davis inequality and asymmetric Kadison inequality. Our results extend some inequalities due to Bourin--Ricard and Furuta.