Renormalization-group approach to a Bose system

The renormalization-group approach is extended to a Bose system within the framework of perturbation theory. Recursion relations are obtained for the parameters of the Hamiltonian and the correlation length index $\nu$ is evaluated. The values of $\nu$ and of the critical exponent $\eta$ (evaluated in an earlier paper) agree with those derived for a classical system characterized by a two-component (real) order parameter. The agreement suggests that the universality hypothesis holds irrespective of the quantum or classical nature of a phase transition.