English

Norm inequalities related to operator monotone functions

Functional Analysis 2021-05-13 v2

Abstract

Let AA be a positive definite operator on a Hilbert space HH, and .|||.||| be a unitarily invariant norm on B(H)B(H). We show that if ff is an operator monotone function on (0,)(0,\infty) and nNn\in \mathbb{N}, then Dnf(A)f(n)(A)|||D^n f(A)|||\leq\|f^{(n)}(A)\| and f(n)()\|f^{(n)}(\cdot)\| is a quasi-convex function on the set of all positive definite operators in B(H)B(H). We establish some estimates of the right hand side of some Hermite-Hadamard type inequalities in which differentiable functions are involved, and norms of the maps induced by them on the set of self adjoint operators are convex, quasi-convex or ss-convex. As applications, we obtain some of bounds for f(B)f(A)|||f(B)-f(A)||| in term of BA|||B-A|||. For instance, Let f,gf,g be two operator monotone functions on (0,)(0,\infty). Then, for every unitarily invariant norm .|||.||| and every positive definite operators A,BA,B, \begin{align*} &\left|\left|\left|f(A)g(A)-f(B)g(B)\right|\right|\right|\notag\\ &\leq|||B-A|||\Big[\max\left\{\|f'(A)\|,\|f'(B)\|\right\}\times\max\left\{\|g(A)\|,\|g(B)\|\right\}\notag\\ &+\max\left\{\|f(A)\|,\|f(B)\|\right\}\times \max\left\{\|g'(A)\|,\|g'(B)\|\right\}\Big]. \end{align*}

Keywords

Cite

@article{arxiv.2008.13226,
  title  = {Norm inequalities related to operator monotone functions},
  author = {Amir Ghasem Ghazanfari},
  journal= {arXiv preprint arXiv:2008.13226},
  year   = {2021}
}
R2 v1 2026-06-23T18:11:35.796Z