Average minimum-degree conjecture for transversal cycle-factors

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 k3k\geq3 and ε>0\varepsilon>0, there exists n0=n0(k,ε)n_0=n_0(k,\varepsilon) such that for every nn0n\geq n_0, if there are numbers δ1,,δkn/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

1ki[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.

Sources & referencesView supporting material

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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