Primitive Monodromy Groups of Rational Functions with One Multiple Pole

Abstract

Primitive monodromy groups of rational functions P/Q, where Q is a polynomial with no multiple roots and deg P > deg Q+1 are classified. There are 17 families of such functions which are not Belyi functions. Only one family from the list contains functions that have five critical values. All the remaining families consist of functions with at most four critical values and constitute one-dimensional strata in the Hurwitz space. The action of the braid group on generators of their monodromy groups is computed and the corresponding megamaps are drawn. The result extends the classification of primitive edge rotation groups of weighted trees obtained by the author and Zvonkin and is also a generalization of the classification of primitive monodromy groups of polynomials obtained by P. Muller.