Transregio Collaboration TRR33

Cosmological inflation, or inflation for short, is the idea that the early universe underwent an epoch of extremely rapid accelerated expansion of space. During this area the volume of the universe grew by a factor of ∼10⁷⁸ within ~^-32 sec. This extreme rapid expansion of the universe ended when the potential energy, driving the rapid exponential expansion, was transferred into radiation. This process is called reheating.

When inflation was introduced in 1980, its main motivation was to solve the magnetic-monopole problem in the big bang theory, i.e. the question of why we do not see any magnetic monopoles today although they should have been produced at a relatively high rate in the very early universe. One might argue that the monopole problem exists only if there is a grand unified theory, inflation provides also a solution to two other classical problems of the big bang scenario: the horizon problem and the flatness problem. The first one is the question of why the CMB is almost isotropic although (without inflation) the horizon is composed out of causally disconnected patches. The second one is a fine-tuning issue, i.e. one would need an extremely accurate adjustment of matter density and kinetic energy in the standard expansion after the big band model to arrive at this hardly measurable space curvature as we observe it today. All these problems are solved by inflation to the extent that due to the huge expansion factor our observable universe today is made out of a very small fraction of space-time after the big bang.

While the predictions of inflation on the initial conditions of the universe are quite robust and model independent, it remains unclear how a concrete model of inflation might be realized. In some of our recent works we approach these and related questions: Fluctuations along supersymmetric flat directions during Inflation, Cosmon Inflation, Fluxbrane Inflation I, and Fluxbrane Inflation II. Our recent discussions also include aspects of reheating, cf. Charge separation in Reheating after Cosmological Inflation.