Accelerated expansion: Theory and observations

The present paradigm, in cosmology is the usual Big-Bang Cosmology in which two stages of accelerated expansion are incorporated: the inflationary pha se in the very early universe which produces the classical inhomogeneities observed in the universe, and a second stage of acceleration at thc, presen t time as the latest Supernovae observations seem to imply. Both stages cou ld be produced by a scalar field and observations will strongly constrain t he microscopic lagrangian, of any proposed model.