Ramanujan Cayley graphs on sporadic groups

Let \Gamma be a k-regular graph with the second maximum  eigenvalue \lambda. Then  \Gamma is said o be Ramanujan graph if \lambda\leq 2\sqrt{k-1}. Let G be a finite group  and \Gamma=Cay(G,S) be a Cayley graph related to G.  The aim of this paper is to investigate the Ramanujan Cayley graphs of sporadic groups.

Ramanujan Cayley graphs on sporadic groups Keywords:

sporadic group , character table , Cayley graph , eigenvalue