Dynamics of the Inflationary Era

We live in a very large, very old, and nearly (perhaps exactly) spatially flat universe. The universe we observe is, at least on large scales, remarkably homogeneous and isotropic. These attributes of our universe can be ascribed to a period of very rapid expansion, or inflation, at some time during the very early history of the universe [1]. A sufficiently long epoch of primordial inflation leads to a homogeneous/isotropic universe that is old and flat. The really good news is that very many reasonable models have been proposed for inflation. In some ways, inflation is generic. That is also the really bad news, since we would like to use the early universe to learn something about physics at energy scales we can’t produce in terrestrial laboratories. We want to know more than just that inflation occurred, we want to learn something of the dynamics of the expansion of the universe during inflation. That may tell us something about physics at very high energies. It would also allow us to restrict the number of inflation models. If we can differentiate between various inflation models, then inflation can be used as a phenomenological guide for understanding physics at very high energies. Oldness, flatness, and homogeneity/isotropy only tell us the minimum length of the inflationary era. They are not very useful instruments to probe the dynamics of inflation. If that is our goal, we must find another tool. In this lecture I will discuss two things associated with inflation that allow us to probe the dynamics of inflation: perturbations and preheating/reheating. While the universe is homogeneous and isotropic on large scales, it is inhomogeneous on small scales. The inhomogeneity in the distribution of galaxies, clusters, and other