Reverse trace inequality for powers greater than one

Let A,B0A,B\geq 0. Let ff be a nonnegative and nondecreasing function on an interval J\mathcal{J} such that spec(A)J\operatorname{spec}(A)\subseteq\mathcal{J}. Reverse trace inequality. One has

Tr[f(A)AsBs]Tr[f(A)(A1/2BA1/2)s],s1.\operatorname{Tr}\left[ f(A) A^s B^s \right] \geq \operatorname{Tr}\left[ f(A) \left(A^{1/2} B A^{1/2} \right)^s \right], \quad \forall\,s\geq 1.

This conjectures the reverse of the proved trace inequality for s[0,1]s\in[0,1]. The authors note that operator convexity of xxsx\mapsto x^s may establish it for s[1,2]s\in[1,2] under a suitable relaxation of an auxiliary theorem's hypotheses; the full range s1s\geq 1 remains open.

Sources & referencesView supporting material

Primary source

Po-Chieh Liu and Hao-Chung Cheng, “On Araki-Type Trace Inequalities”, arXiv:2507.05242 (2025).

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