On reverses of the Golden-Thompson type inequalities

TL;DR

This paper establishes new reverse inequalities related to the Golden-Thompson inequality for Hermitian matrices, involving spectral bounds, Specht's ratio, and the Olson order, improving upon existing results.

Contribution

It introduces novel reverse inequalities of the Golden-Thompson type using spectral bounds and matrix means, enhancing previous bounds with sharper constants.

Findings

Derived new spectral inequalities for Hermitian matrices.

Improved bounds involving Specht's ratio and Olson order.

Extended inequalities with alternative constants.

Abstract

In this paper we present some reverses of the Golden-Thompson type inequalities: Let $H$ and $K$ be Hermitian matrices such that $ e^s e^H \preceq_{ols} e^K \preceq_{ols} e^t e^H$ for some scalars $s \leq t$, and $\alpha \in [0 , 1]$. Then for all $p>0$ and $k =1,2,\ldots, n$ \begin{align*} \label{} \lambda_k (e^{(1-\alpha)H + \alpha K} ) \leq (\max \lbrace S(e^{sp}), S(e^{tp})\rbrace)^{\frac{1}{p}} \lambda_k (e^{pH} \sharp_\alpha e^{pK})^{\frac{1}{p}}, \end{align*} where $A\sharp_\alpha B = A^\frac{1}{2} \big ( A^{-\frac{1}{2}} B^\frac{1}{2} A^{-\frac{1}{2}} \big) ^\alpha A^\frac{1}{2}$ is $\alpha$-geometric mean, $S(t)$ is the so called Specht's ratio and $\preceq_{ols}$ is the so called Olson order. The same inequalities are also provided with other constants. The obtained inequalities improve some known results.