Minimax exclusivity conjecture for power-type losses

Let p,q>0p,q>0 be distinct exponents, and for each r>0r>0 let Lr\mathcal{L}_r be the class of losses whose local behavior near a=θa=\theta is c(θ)∣θ−a∣r+o(∣θ−a∣r)c(\theta)|\theta-a|^r+o(|\theta-a|^r) with c(θ)>0c(\theta)>0. Consider minimax optimality over a regular parametric model. Minimax exclusivity conjecture. No estimator is simultaneously minimax for a loss in Lp\mathcal{L}_p and a loss in Lq\mathcal{L}_q. Equivalently, the family {Lr:r>0}\{\mathcal{L}_r:r>0\} forms a minimax exclusivity partition of Lpower=⋃r>0Lr\mathscr{L}_{\mathrm{power}}=\bigcup_{r>0}\mathcal{L}_r. The structural classes are disjoint and closed cones under positive scaling, but whether their structural separation forces minimax exclusivity remains unclear.

References

Primary source

Stanisław M. S. Halkiewicz, “Exclusivity Classes and Partitions of Loss Functions”, arXiv:2507.12447 (2026).

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