Stochastic fluctuations and structure formation in the Universe

It is shown that the evolution of the density perturbations during certain eras of substantial entropy generation in the universe can be described in the scheme of the KPZ equation. Therefore, the influence on cosmological structure formation by stochastic forces arising from various dissipations can be studied through the universal characteristics of surface growth in $d=3+1$ dimensions. We identify eras of strong stochastic fluctuations and describe dynamically how these other dissipative sources of noise, besides initial (inflationary) quantum fluctuations, generate seeds of density perturbation with power law spectrum, including the Harrison-Zeldovich spectrum.