  A multicanonical formalism is applied to the problem of statistical
equilibrium in a complex system with a hierarchy of dynamical structures. At
the small scales the system is in quasi-equilibrium and follows a
Maxwell-Boltzmann distribution with a slowly fluctuating temperature. The
probability distribution for the temperature is determined using Bayesian
analysis and it is then used to average the Maxwell-Boltzmann distribution. The
resulting energy distribution law is written in terms of generalized
hypergeometric functions, which display power-law tails.
