Characterization of the monotonicity by the inequality
  Let $\varphi$ be a normal state on the algebra $B(H)$ of all bounded operators on a Hilbert space $H$, $f$ a strictly positive, continuous function on $(0, \infty)$, and let $g$ be a function on $(0, \infty)$ defined by $g(t) = \frac{t}{f(t)}$. We will give characterizations of matrix and operator monotonicity by the following generalized Powers-St\ormer inequality:   $$ \varphi(A + B) - \varphi(|A - B|) \leq 2\varphi(f(A)^1/2g(B)f(A)^1/2), $$ whenever $A, B$ are positive invertible operators in $B(H).$ 
Dinh Trung Hoa, Hiroyuki Osaka, and Jun Tomiyama
math.FA math.OA