English

On Degree Powers in Intersecting Families

Combinatorics 2026-07-30 v1

Abstract

For a family F([n]k)\mathcal{F}\subseteq\binom{[n]}k and R([n]r)R\in\binom{[n]}r, let dF(R)={FF:RF}d_{\mathcal{F}}(R)=|\{F\in\mathcal{F}:R\subseteq F\}| and r,p(F)=R([n]r)dF(R)p\ell_{r,p}(\mathcal{F})=\sum_{R\in\binom{[n]}r}d_{\mathcal{F}}(R)^p; at the codegree level we write cop(F)=k1,p(F)co_p(\mathcal{F})=\ell_{k-1,p}(\mathcal{F}). We develop a discrete two-moment interpolation principle that majorizes xpx^p on the integer degree lattice by a quadratic interpolant and reduces every real exponent p2p\geq2 to sharp bounds for the first two falling moments. We prove that a full tt-star maximizes copco_p among tt-intersecting families for every real p2p\geq2 throughout the sharp classical range n(t+1)(kt+1)n\geq(t+1)(k-t+1), and we determine all equality cases. Using Bey's size-sensitive quadratic inequality, we extend the same framework to every nontrivial degree level: if F\mathcal{F} is intersecting, n2kn\geq2k, and 1rk11\leq r\leq k-1, then a full point-star maximizes r,p(F)\ell_{r,p}(\mathcal{F}) for every real p2p\geq2, again with a complete equality classification. Thus the codegree theorem extends the sharp Wu--Zhang quadratic bound to every real p2p\geq2, completes the quadratic boundary equality classification, contains the Brooks--Linz conjecture as its p=2p=2 special case, and, for integer exponents p2p\geq2, resolves the problem of Zhou--Yuan throughout the sharp Erd\H{o}s--Ko--Rado range.

Cite

@article{arxiv.2607.28616,
  title  = {On Degree Powers in Intersecting Families},
  author = {Mengyu Cao and Mei Lu and Haixiang Zhang},
  journal= {arXiv preprint arXiv:2607.28616},
  year   = {2026}
}