Sublinear type-2 growth for the identity into the smallest valid norm

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Let XX be a valid norm, meaning a norm on S1k~′ ⁣,n⊗S1k~′ ⁣,n⊗ℓ2kk~′\mathcal{S}_1^{\tilde k'\!, n}\otimes\mathcal{S}_1^{\tilde k'\!, n}\otimes\ell_2^{k\tilde k'} satisfying

∥x∥X≳∥x∥Xiii\|x\|_X\gtrsim\|x\|_{X^{iii}}

for every xx, together with

∥∣i⟩⊗∣j⟩⊗(V∣ij⟩⊗Id⁡ℓ2k~′)∥X≤1\left\|\lvert i\rangle\otimes\lvert j\rangle\otimes\left(V\lvert ij\rangle\otimes\operatorname{Id}_{\ell_2^{\tilde k'}}\right)\right\|_X\leq1

for every V∈BMn2k,k~′V\in B_{M_{n^2k,\tilde k'}} and i,j=1,…,ni,j=1,\ldots,n. Let Id⁡:X→Xiii\operatorname{Id}:X\to X^{iii} be the identity map between the same underlying vector space equipped with these norms, and let T2(n2)\mathrm{T}_2^{(n^2)} denote its type-2 constant restricted to n2n^2 vectors. Identity-map conjecture. There exists a valid norm XX and a dimension-independent constant β<1\beta<1 such that

T2(n2)(Id⁡:X→Xiii)≲log⁡nβ.\mathrm{T}_2^{(n^2)}\left(\operatorname{Id}:X\to X^{iii}\right)\lesssim_{\log}n^\beta.

This is the final and weakest form proposed in the source; it would imply the desired lower bounds for position-based cryptography. No resolution is given.

References

Primary source

Marius Junge, Aleksander M. Kubicki, Carlos Palazuelos and David Pérez-García, “Geometry of Banach spaces: a new route towards Position Based Cryptography”, arXiv:2103.16357 (2022).

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