Multiple-copy Ramsey numbers for loose and tight hypergraph paths and cycles

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Let R(F,G)R(\mathcal{F},\mathcal{G}) denote the Ramsey number for hypergraphs, and let mFm\mathcal{F} denote the disjoint union of mm copies of F\mathcal{F}. For kk-uniform hypergraphs, write Prk\mathcal{P}_r^k, Crk\mathcal{C}_r^k, and P^rk\hat{\mathcal{P}}_r^k for the relevant path and cycle hypergraphs.

Multiple-copy path and cycle conjecture. For every k≥3k\geq 3, m≥nm\geq n and r≥s≥3r\geq s\geq 3,

R(mPrk,nPsk)=R(mPrk,nCsk)=((k−1)r+1)m+⌊s+12⌋n−1,R(m\mathcal{P}_r^k,n\mathcal{P}_s^k)=R(m\mathcal{P}_r^k,n\mathcal{C}_s^k)=((k-1)r+1)m+\Big\lfloor\frac{s+1}{2}\Big\rfloor n-1, R(mP^rk,nP^sk)=(r+k−1)m+(1+⌊s−1k⌋)n−1,R(m\hat{\mathcal{P}}_r^k,n\hat{\mathcal{P}}_s^k)=(r+k-1)m+(1+\lfloor\frac{s-1}{k}\rfloor)n-1, R(mCrk,nCsk)=(k−1)rm+⌊s+12⌋n−1,R(m\mathcal{C}_r^k,n\mathcal{C}_s^k)=(k-1)rm+\Big\lfloor\frac{s+1}{2}\Big\rfloor n-1,

and, if r>sr>s,

R(mCrk,nPsk)=(k−1)rm+⌊s+12⌋n−1.R(m\mathcal{C}_r^k,n\mathcal{P}_s^k)=(k-1)rm+\Big\lfloor\frac{s+1}{2}\Big\rfloor n-1.

The first and third formulas extend the established k=3k=3 results and the lower bound for multiple loose cycles; determining whether the natural lower bound is always exact remains open in general, with analogous questions for loose paths, tight paths, and tight cycles.

References

Primary source

Gholam Reza Omidi and Ghaffar raeisi, “Ramsey numbers for multiple copies of hypergraphs”, arXiv:1303.0474 (2013).

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