The $d$-chromatic Ramsey number for stars

TL;DR

This paper investigates the $d$-chromatic Ramsey numbers for stars, providing exact values for certain cases and extending the understanding of these generalized Ramsey numbers in multi-color settings.

Contribution

The paper determines all values of $r^{d,c}(K_{1,n})$, $r_{*}^{d,c}(K_{1,n})$, and partially for $r^{d,c}(K_{1,n_1}, \

Findings

Exact values for $r^{d,c}(K_{1,n})$ and $r_{*}^{d,c}(K_{1,n})$ are established.

Partial results are obtained for the $d$-chromatic Ramsey number of multiple stars.

The work extends classical Ramsey theory to the context of $d$-chromatic and star graphs.

Abstract

In 1978, Chung and Liu generalized the definition of the Ramsey number. They introduced the $d$-chromatic Ramsey number as follows. Let $1\leq d< c$ be integers and let $A_{1}, \dots, A_{t}$ be subsets with size $d$ of $[c]$, where $t= {c\choose d}$. For given graphs $G_{1}, \dots, G_{t}$, {\it the $d$-chromatic Ramsey number}, $r^{d, c}(G_{1}, \dots, G_{t})$, is the minimum positive integer $N$ such that every $c$-coloring of $E(K_{N})$ yields a copy of $G_{i}$ whose edges are colored by colors in the color set $A_{i}$ for some $i\in [t]$. The {\it star-critical $d$-chromatic Ramsey number}, $r_{*}^{d, c}(G_{1}, \dots, G_{t})$, is the minimum positive integer $k$ such that every $c$-coloring of $E(K_{N}- K_{1, N- 1- k})$ yields a copy of $G_{i}$ whose edges are colored by colors in the color set $A_{i}$ for some $i\in [t]$, where $N= r^{d, c}(G_{1}, \dots, G_{t})$. If $G_{1}, \dots, G_{t}= G$, then we simplify them as $r^{d, c}(G)$ (it also call {\it the weakened Ramsey number}) and $r^{d, c}_{*}(G)$, respectively. In this paper, we determine all the value of $r^{d, c}(K_{1, n})$, $r_{*}^{d, c}(K_{1, n})$ and part of the value of $r^{d, c}(K_{1, n_{1}}, \dots, K_{1, n_{t}})$.