## Strong Interactions for Cosmology

Who: Jakob Jark Jørgensen (CP3-Origins)
When: Wednesday, April 15, 2015

Jakob Jark Jørgensen‘s advisor was Francesco Sannino.

Abstract:

In this work we analyze single field slow-roll models of inflation with an explicit non-minimal coupling to gravity. We will introduce the non-minimal coupling by doing large field inflation on a quartic potential and find that it leads to a lowering of the tensor-to-scalar ratio as compared to the minimally coupled case. It may also alleviate the problem of tiny values of the inflaton self-coupling. However, this comes at the cost of a very large non-minimal coupling $$\xi \sim 10^4$$. We will use this example as template for models of composite inflation. We consider models where the inflaton emerges as a composite scalar field in a low-energy effective field theory description of an underlying gauge dynamics, which is free from fundamental scalars. We will find that inflation may be realizes in a pure Yang-Mills theory, where the inflaton emerges as a glueball, as well as in technicolor-like models, where the inflaton emerges in a manner similar to the composite Higgs of Minimal Walking Technicolor. Also, we will describe corrections on top of a quartic potential with non-minimal coupling, and find that even small quantum correction may shift the tensor-to-scalar ratio significantly towards higher values. We compare this discussion with $$f(R)$$-theories of inflation, in particular the Starobinsky model. We argue that corrections stemming from integrating out matter fields embedded in the gravitational theory, may be probed in the $$(r,n_s)$$-plane if inflation is driven by a $$f(R)$$-theory of gravity.

We start the thesis by providing a careful review of the inflationary paradigm. First we consider the perfectly homogeneous and isotropic universe and introduce inflation as a resolution to concerns about the initial conditions necessary for Big Bang cosmology. Next we consider perturbations on top of the homogeneous background and explain that inflation may also serve as a theory for the origin of structure in the universe.

The PhD thesis is available as a PDF file.