13 - Structure Formation in the Early Universe

Summary

Structure formation in the early universe is a key problem in modern cosmology. In this chapter we discuss stochastic gravity as an alternative framework for studying the generation of primordial inhomogeneities in inflationary models, which can easily incorporate effects that go beyond the linear perturbations of the inflaton field. We show that the correlation functions that follow from the Einstein–Langevin equation, which emerge in the framework of stochastic gravity, coincide with that obtained with the usual quantization procedures when both the metric perturbations and the inflaton fluctuations are linear. Stochastic gravity, however, can also deal very naturally with the fluctuations of the inflaton field beyond the linear approximation. Here, we illustrate the stochastic approach with one of the simplest chaotic inflationary models in which the background spacetime is a quasi de Sitter universe, and prove the equivalence of the stochastic and quantum correlations to the linear order.