On Densities for Solutions to Stochastic Fixed Point Equations

We consider systems of stochastic fixed-point equations that arise in the asymptotic analysis of random recursive structures and algorithms such as Quicksort, generalized P\'olya urn processes and path lengths of random recursive trees and split trees. Based on an approach of Fill and Janson for the analysis of the Quicksort-limit, the main result of this paper is the existence of bounded, smooth, rapidly decreasing density functions for limits given by these kinds of limit equations.