English

Berge tight cycles of all lengths in hypergraphs

Combinatorics 2026-06-29 v1

Abstract

Given a set RR of positive integers, an RR-graph H=(V,E)H = (V, E) is a hypergraph where the cardinality of each hyperedge belongs to RR. If R={r}R = \{r\}, we sometimes refer to the hypergraph as an rr-graph rather than an RR-graph. For a set SVS \subseteq V, let dH(S)d_H(S) denote the number of hyperedges of HH containing SS. Given a nonnegative integer ss, the minimum ss-degree δs(H)\delta_s(H) is the minimum of dH(S)d_H(S) over all ss-vertex subsets SS of VV. Let rr and tt be positive integers with r<tr < t. We denote by CtrC_t^r the tt-vertex rr-uniform tight cycle, which is an rr-graph with at least three hyperedges whose vertices admit a cyclic ordering such that every rr consecutive vertices form a hyperedge. In particular, Ct2C_t^2 is the classical cycle CtC_t in 22-graphs. For hypergraphs FF and HH, we say that HH is a Berge-FF if there exist an injection f ⁣:V(F)V(H)f \colon V(F) \to V(H) and a bijection g ⁣:E(F)E(H)g \colon E(F) \to E(H) such that {f(v):ve}g(e)\{f(v): v \in e\} \subseteq g(e) for all eE(F)e \in E(F). Lu and Wang [Discrete Math. 344 (2021), 112462] proved that every [3][3]-graph HH on n6n \geq 6 vertices with δ2(H)1\delta_2(H) \geq 1 contains a Berge-CtC_t for all 3tn3 \leq t \leq n. In this paper, we prove that for any positive integer rr and any set R[k]R \subseteq [k] with k2k \geq 2, there exists an integer n0=n0(k,r)n_0 = n_0(k,r) such that every RR-graph HH on nn0n \geq n_0 vertices with δr(H)1\delta_r(H) \geq 1 contains a Berge-CtrC_t^r for all r+1tnr+1 \leq t \leq n. In particular, when k=4k = 4 and r=3r = 3, we show that every [4][4]-graph HH on n9n \geq 9 vertices with δ3(H)1\delta_3(H) \geq 1 contains a Berge-Ct3C_t^3 for all 4tn4 \leq t \leq n. We also characterize all the counterexamples when 4n84 \leq n \leq 8.

Keywords

Cite

@article{arxiv.2606.30418,
  title  = {Berge tight cycles of all lengths in hypergraphs},
  author = {Yu Minghui and Li Binlong and Li Ruonan},
  journal= {arXiv preprint arXiv:2606.30418},
  year   = {2026}
}

Comments

17 pages