Let $G$ be a finite group and $\text{ cd}(G)$ denote the character degree set for $G$. The prime graph $\Delta(G)$ is a simple graph whose vertex set consists of prime divisors of elements in $\text{ cd}(G)$, denoted $\rho(G)$. Two primes $p,q\in \rho(G)$ are adjacent in $\Delta(G)$ if and only if $pq|a$ for some $a\in \text{ cd}(G)$. We determine which simple 4-regular graphs occur as prime graphs for some finite nonsolvable group.
Categories: math.RT math.GR