Cosmology is a precision discipline with a large amount of data of ever increasing accuracy becoming available. These data are remarkably well fit by the ¤CDM cosmology, a relatively simple model with a few adjustable parameters. The biggest drawback of ¤CDM is that it is unknown what is ¤, and what is CDM. Indeed, the cosmological constant problem and the nature of dark matter are considered by many to be the greatest mysteries of modern physics.
Another mystery is the very mechanism by which a flat and homogeneous Universe filled with matter was created a short instant after the Big Bang. The currently most widely accepted explanation is that the Universe underwent a very rapid phase of expansion before matter had cooled enough for atomic nuclei to form. This phase of expansion has been called "inflation" and has been successful also to explain other observations, such as the typical sizes of structures that we see in the Universe. Inflation also predicts the generation of small ripples in space that originate from quantum fluctuations in the very early universe and that later, after the Universe has cooled down, leave marks in the cosmic microwave background radiation. However, there isn't presently one model of inflation, but several. Concrete realizations of inflation rely on input from Quantum Field Theory and particle physics. Possible scenarios that range from very economic that do not require any new physics, where inflation is driven by the Higgs field of the Standard Model, to constructions motivated or directly implied by String Theory, where the physics of the early Universe is ultimately governed by Quantum Gravity. To really understand what happened in the early Universe we have to find a way to distinguish which model is correct. This can only be done by working out the predictions of these models and by contrasting them with data.
The Nordita Cosmology group works on inflationary models, and in particular on their predictions for primordial non-Gaussianities in the cosmic microwave background, on String Cosmology, and on the physics of Dark Matter, with focus on the axion dark matter, including the role axions play in Astrophysics.
