Schwinger Boson Formulation and Solution of the Crow-Kimura and Eigen   Models of Quasispecies Theory
  We express the Crow-Kimura and Eigen models of quasispecies theory in a functional integral representation. We formulate the spin coherent state functional integrals using the Schwinger Boson method. In this formulation, we are able to deduce the long-time behavior of these models for arbitrary replication and degradation functions.   We discuss the phase transitions that occur in these models as a function of mutation rate. We derive for these models the leading order corrections to the infinite genome length limit. 
Jeong-Man Park and Michael W. Deem