Critical-parameter limit for the measure of t-intersecting subspaces

From papers

Let tt be a fixed positive integer. Let Ωn\Omega_n be the set of all subspaces of an nn-dimensional vector space over the field with qq elements, let An(t)A_n^{(t)} be the family of subspaces containing a fixed tt-dimensional subspace, and define

f(n,t,σ)=maxμσ(U)1/n:UΩn is t-intersecting.f(n,t,\sigma)=\max\\{\mu_{\sigma}(U)^{1/n}: U\subset\Omega_n\text{ is }t\text{-intersecting}\\}.

Write σθ,n=q(1θ)n\sigma_{\theta,n}=q^{-(1-\theta)n} and μθ,n=μσθ,n\mu_{\theta,n}=\mu_{\sigma_{\theta,n}}. The critical-parameter limit conjecture.

limnf(n,t,σ12,n)=q12t.\lim_{n\to\infty}f(n,t,\sigma_{\frac{1}{2},n})=q^{-\frac{1}{2}t}.

The theorem immediately preceding this statement establishes the corresponding limits away from the critical value θ=12\theta=\frac12; this conjecture concerns the remaining boundary case and is presented as the expected critical asymptotic.

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Sources & referencesView supporting material

Primary source

Hajime Tanaka and Norihide Tokushige, “Extremal problems for intersecting families of subspaces with a measure”, arXiv:2404.17385 (2025).

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