##### Department of Mathematics,

University of California San Diego

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### Math 269 - Seminar in Combinatorics

## Zhifei Yan

#### IMPA, Rio de Janeiro (zhifei.yan@impa.br)

## The chromatic number of very dense random graphs

##### Abstract:

The chromatic number of a very dense random graph $G(n,p)$, with $p \ge 1 - n^{-c}$ for some constant $c > 0$, was first studied by Surya and Warnke, who conjectured that the typical deviation of $\chi(G(n,p))$ from its mean is of order $\sqrt{\mu_r}$, where $\mu_r$ is the expected number of independent sets of size $r$, and $r$ is maximal such that $\mu_r > 1$, except when $\mu_r = O(\log n)$. They moreover proved their conjecture in the case $n^{-2} \ll 1 - p = O(n^{-1})$.

In this talk, we study $\chi(G(n,p))$ in the range $n^{-1}\log n \ll 1 - p \ll n^{-2/3}$, that is, when the largest independent set of $G(n,p)$ is typically of size 3. We prove in this case that $\chi(G(n,p))$ is concentrated on some interval of length $O(\sqrt{\mu_3})$, and for sufficiently `smooth' functions $p = p(n)$, that there are infinitely many values of $n$ such that $\chi(G(n,p))$ is not concentrated on any interval of size $o(\sqrt{\mu_3})$. We also show that $\chi(G(n,p))$ satisfies a central limit theorem in the range $n^{-1} \log n \ll 1 - p \ll n^{-7/9}$.

This talk is based on arXiv:2405.13914

### October 15, 2024

### 2:00 PM

AP&M 7321 (**Zoom-Talk**: **Meeting ID**: 941 1988 0012, **Password**: 634921)

Research Areas

Combinatorics Probability Theory****************************