Conjectured sharp constant for Schatten-norm commutator inequalities

About 17 years old · traced to

Let XX and YY be general square matrices, and let p,q,r≥1p,q,r\geq 1 satisfy

1p≤1q+1r.\frac{1}{p}\leq\frac{1}{q}+\frac{1}{r}.

Write ∥⋅∥s\lVert\cdot\rVert_s for the Schatten ss-norm, and let cp,q,rc_{p,q,r} be the smallest constant such that

∥[X,Y]∥p≤cp,q,r∥X∥q∥Y∥r.\lVert[X,Y]\rVert_p\leq c_{p,q,r}\lVert X\rVert_q\lVert Y\rVert_r.

Schatten-norm commutator conjecture. In the restricted case p=qp=q,

cp,q,r=cp,p,r=2max⁡(1/p,1−1/p,1−1/r).c_{p,q,r}=c_{p,p,r}=2^{\max(1/p,1-1/p,1-1/r)}.

This is a proposed sharp-constant formula extending the Böttcher–Wenzel inequality to different Schatten norms. The source presents it as a conjecture based on numerical experiments; no resolution is supplied in the given text.

References

Primary source

Koenraad M. R. Audenaert, “Variance bounds, with an application to norm bounds for commutators”, arXiv:0907.3913 (2009).

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