Postponement of Hopf bifurcations by multiplicative colored noise

Problems related to the definition of a Hopf bifurcation in the presence of noise are discussed in terms of three physical observables: the correlation functions, the power spectra, and the statistical densities. Of these, only the statistical density exhibits a distinct noise-induced transition. For a specific definition, only postponements are observed in analog simulator experiments with a Brusselator subject to white and colored noise on the control parameter. A recent prediction due to Lefever and Turner [Phys. Rev. Lett. 56, 1631 (1986)] is qualitatively tested.