English

Clique factors in Kneser graphs

Combinatorics 2019-11-27 v2

Abstract

For k,nNk,n\in \mathbb{N}, the Kneser graph K(n,k)K(n,k) is the graph with vertex set V=[n](k)V=[n]^{(k)} and edge set E={{x,y}V(2):xy=}E=\{\{x,y\} \in V^{(2)}: x\cap y=\emptyset\}. Chen proved that for n3kn\geq 3k, Kneser graphs are Hamiltonian. Similarly as for graphs with Hajnal's and Szemer\'edi's result about a minimum degree condition for clique factors and the P\'osa-Seymour Conjecture together with its solution for large graphs due to Koml\'os, S\'ark\"ozy, and Szemer\'edi, the next step is to ask for clique factors and powers of Hamiltonian cycles in Kneser graphs. For k,Nk,\ell\in \mathbb{N}, let n(k,)n(k,\ell) be the smallest integer such that for nn(k,)n\geq n(k,\ell), K(n,k)K(n,k) contains the \ell-th power of a Hamiltonian cycle. Katona conjectured that for all but finitely many exceptions, n(k,)=(+1)k+1n(k,\ell)=(\ell+1)k+1 holds. In particular, it would be interesting to know whether n(k,)n(k,\ell) is linear in kk (for fixed \ell). So far this is not known for k2k\geq 2. In this note, we take a first step towards such a linear bound by proving that for N\ell\in \mathbb{N}, kk\geq \ell and n3kn\geq \ell ^3k, all but at most 1\ell-1 vertices of K(n,k)K(n,k) can be partitioned into cliques of size \ell. Further, we use our methods to extend a short proof due to Chen and F\"uredi that K(n,k)K(n,k) is Hamiltonian for n3kn\geq 3k and knk \mid n to all n4kn\geq 4k if k4k\geq 4.

Keywords

Cite

@article{arxiv.1911.10190,
  title  = {Clique factors in Kneser graphs},
  author = {Johann Bellmann and Bjarne Schülke},
  journal= {arXiv preprint arXiv:1911.10190},
  year   = {2019}
}

Comments

The main result follows directly from Baranyai's theorem and this paper has been withdrawn

R2 v1 2026-06-23T12:24:50.278Z