Average minimum-degree conjecture for transversal cycle-factors

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Let CkC_k be the cycle on kk vertices, and let the nn-blow-up of CkC_k have parts V1,…,VkV_1,\dots,V_k, each of size nn. For a spanning subgraph GG, let δ(G[Vi,Vi+1])\delta(G[V_i,V_{i+1}]) denote the minimum degree in the bipartite graph between consecutive parts, with indices taken modulo kk. A transversal CkC_k-factor is a collection of nn vertex-disjoint copies of CkC_k, each using one vertex from every part.

Average minimum-degree conjecture. For every k≥3k\geq3 and ε>0\varepsilon>0, there exists n0=n0(k,ε)n_0=n_0(k,\varepsilon) such that for every n≥n0n\geq n_0, if there are numbers δ1,…,δk≥n/2\delta_1,\dots,\delta_k\geq n/2 satisfying

δ(G[Vi,Vi+1])≥δifor every i∈[k]\delta(G[V_i,V_{i+1}])\geq\delta_i\quad\text{for every }i\in[k]

and

1k∑i∈[k]δi≥(1+1k+ε)n2,\frac{1}{k}\sum_{i\in[k]}\delta_i\geq\left(1+\frac{1}{k}+\varepsilon\right)\frac{n}{2},

then GG has a transversal CkC_k-factor.

This conjecture strengthens the paper's asymptotic theorem by replacing a uniform degree condition with an average condition across the consecutive pairs. The preceding example shows that the corresponding threshold is close to best possible.

References

Primary source

Beka Ergemlidze and Theodore Molla, “Transversal C_k-factors in subgraphs of the balanced blow-up of C_k”, arXiv:2103.09745 (2021).

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