Checkerboard Julia sets for rational maps

Abstract

In this paper, we consider the family of rational maps

F-lambda(z) = z(n) + lambda/z(d),

where n >= 2, d >= 1, and lambda is an element of C. We consider the case where lambda lies in the main cardioid of one of the n - 1 principal Mandelbrot sets in these families. We show that the Julia sets of these maps are always homeomorphic. However, two such maps F-lambda and F-mu are conjugate on these Julia sets only if the parameters at the centers of the given cardioids satisfy mu = nu(j(d+1))lambda or mu = nu(j(d+1))(lambda) over bar where j is an element of Z and nu is an (n - 1)th root of unity. We define a dynamical invariant, which we call the minimal rotation number. It determines which of these maps are conjugate on their Julia sets, and we obtain an exact count of the number of distinct conjugacy classes of maps drawn from these main cardioids.