Large-pp conjecture for Turán densities of uniform hypergraphs

Let XX be a finite set, and let H(Xr)\mathcal{H}\subseteq\binom{X}{r} be an rr-uniform hypergraph. For integers qpr2q\geq p\geq r\geq2, say that H\mathcal{H} has the (q,p)(q,p)-property if every qq-vertex subset contains a pp-vertex clique. Define

Tr(n,q,p)=min{H:H([n]r) has the (q,p)-property},T_r(n,q,p)=\min\{\lvert\mathcal{H}\rvert:\mathcal{H}\subseteq\binom{[n]}{r}\text{ has the }(q,p)\text{-property}\},

and tr(q,p)=limnTr(n,q,p)/(nr)t_r(q,p)=\lim_{n\to\infty}T_r(n,q,p)/\binom{n}{r}. Large-pp conjecture. For integers r2r\geq2 and pp sufficiently large,

tr(2p+1,p+1)=12r1.t_r(2p+1,p+1)=\frac{1}{2^{r-1}}.

The paper proves the corresponding assertion for r=3r=3 when p3p\geq3, while p=2p=2 corresponds to Turán's open K53K_5^3 problem. The r=4,p=3r=4,p=3 case is explicitly reported to fail, so the claim is restricted to sufficiently large pp.

Sources & referencesView supporting material

Primary source

Peter Frankl, Hao Huang and Vojtěch Rödl, “On local Turán problems”, arXiv:2004.08734 (2020).

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