Licentiate thesis: Effective Field Theory and the Early Universe

by Stefan E. Sjörs (Stockholm University, Department of Physics)

Monday 14 Sept 2009, 15:30 → 17:00 Europe/Stockholm

FB54

In this thesis I discuss two aspects of the physics of the early universe within the language of effective field theory. The first part is devoted to dark matter and we study thermal neutralino dark matter in an effective field theory extension of the MSSM, called "Beyond the MSSM" (BMSSM) in Dine, Seiberg and Thomas (2007). In this class of effective field theories, the field content of the MSSM is unchanged, but the little hierarchy problem is alleviated by allowing small corrections to the Higgs/higgsino part of the Lagrangian. We perform parameter scans and compute the dark matter relic density. The light higgsino LSP scenario is modified the most; we find new regions of parameter space compared to the standard MSSM. This involves interesting interplay between the WMAP dark matter bounds and the LEP chargino bound. We also find some changes for gaugino LSPs, partly due to annihilation through a Higgs resonance, and partly due to coannihilation with light top squarks in models that are ruled in by the new effective terms. The second part is devoted to the inflationary idea of the early universe and it is pointed out that in the string model of inflationary cosmology known as axion monodromy, inflation naturally generalizes to a two-field model with a specific "spiral Staircase" potential. In this generalization, it appears that we can generate measurable gravitational waves in the cosmic microwave background even for small (sub-Planckian) vacuum expectation values, unlike all previously known models of inflation. The slow-roll conditions for axion monodromy also appear in a different light in the multi-field framework.