English

Star-critical Gallai-Ramsey numbers of graphs

Combinatorics 2021-03-03 v1

Abstract

The Gallai-Ramsey number grk(K3:H1,H2,,Hk)gr_{k}(K_{3}: H_{1}, H_{2}, \cdots, H_{k}) is the smallest integer nn such that every kk-edge-colored KnK_{n} contains either a rainbow K3K_3 or a monochromatic HiH_{i} in color ii for some i[k]i\in [k]. We find the largest star that can be removed from KnK_n such that the underlying graph is still forced to have a rainbow K3K_3 or a monochromatic HiH_{i} in color ii for some i[k]i\in [k]. Thus, we define the star-critical Gallai-Ramsey number grk(K3:H1,H2,,Hk)gr_{k}^{*}(K_3: H_{1}, H_{2}, \cdots, H_{k}) as the smallest integer ss such that every kk-edge-colored KnK1,n1sK_{n}-K_{1, n-1-s} contains either a rainbow K3K_3 or a monochromatic HiH_{i} in color ii for some i[k]i\in [k]. When H=H1==HkH=H_{1}=\cdots=H_{k}, we simply denote grk(K3:H1,H2,,Hk)gr_{k}^{*}(K_{3}: H_{1}, H_{2}, \cdots, H_{k}) by grk(K3:H)gr_{k}^{*}(K_{3}: H). We determine the star-critical Gallai-Ramsey numbers for complete graphs and some small graphs. Furthermore, we show that grk(K3:H)gr_{k}^{*}(K_3: H) is exponential in kk if HH is not bipartite, linear in kk if HH is bipartite but not a star and constant (not depending on kk) if HH is a star.

Keywords

Cite

@article{arxiv.2103.01508,
  title  = {Star-critical Gallai-Ramsey numbers of graphs},
  author = {Xueli Su and Yan Liu},
  journal= {arXiv preprint arXiv:2103.01508},
  year   = {2021}
}

Comments

19 pages, 1 figure