On the Irreducibility of Perron Representations of Degrees 4 and 5

Abstract

We consider the graph $E_{n+1,1}$ with (n+1) generators ${\sigma }_1,...,{\sigma }_n$, and $\delta$, where ${\sigma }_i$ has an edge with ${\sigma }_{i+1}$ for $i=1,...,n+1$, and ${\sigma }_1$ has an edge with $\delta$. We then define the Artin group of the graph $E_{n+1,1}$ for $n=3$ and $n=4$ and consider its reduced Perron's representation of degrees
four and five respectively. After we specialize the indeterminates used in defining the representation to non-zero complex numbers, we obtain necessary and sufficient
conditions that guarantee the irreducibility of the representations for $n=3$ and $4$ .