Some inequalities for operator (p,h)-convex functions

TL;DR

This paper introduces and studies a new class of operator convex functions called operator (p,h)-convex functions, establishing key inequalities and characterizations, and exploring their connections with operator monotone functions.

Contribution

It defines operator (p,h)-convex functions, proves Jensen and Hansen-Pedersen type inequalities, and provides equivalent conditions and applications including Choi-Davis-Jensen inequalities.

Findings

Established Jensen and Hansen-Pedersen inequalities for operator (p,h)-convex functions.

Derived equivalent conditions characterizing operator (p,h)-convexity.

Connected operator (p,h)-convex functions with operator monotone functions.

Abstract

Let $p$ be a positive number and $h$ a function on $\mathbb{R}^+$ satisfying $h(xy) \ge h(x) h(y)$ for any $x, y \in \mathbb{R}^+$. A non-negative continuous function $f$ on $K (\subset \mathbb{R}^+)$ is said to be {\it operator $(p,h)$-convex} if \begin{equation*}\label{def} f ([\alpha A^p + (1-\alpha)B^p]^{1/p}) \leq h(\alpha)f(A) +h(1-\alpha)f(B) \end{equation*} holds for all positive semidefinite matrices $A, B$ of order $n$ with spectra in $K$, and for any $\alpha \in (0,1)$. In this paper, we study properties of operator $(p,h)$-convex functions and prove the Jensen, Hansen-Pedersen type inequalities for them. We also give some equivalent conditions for a function to become an operator $(p,h)$-convex. In applications, we obtain Choi-Davis-Jensen type inequality for operator $(p,h)$-convex functions and a relation between operator $(p,h)$-convex functions with operator monotone functions.