Talks

Cosmology and quantum gravity have not always had the smoothest of interactions. As a case in point I'll summarize the calculation behind the prediction of tensor modes in inflationary universes and discuss the difficulties found in recasting this calculation in terms of Ashtekar-Barbero-Immirzi variables. Contrary to the belief that ``inflation is shielded from quantum gravity'', novelties are found, leading to the interesting prediction of a chiral signature in the gravitational wave background, proportional to the imaginary part of the Immirzi parameter. This would leave a distinctive imprint in the polarization of the cosmic microwave background. On a more theoretical level, our remarks shed light on matters permeating quantum gravity, such as the inner product, the ground state (which we prove is NOT the Kodama state) and ordering issues.

In recent years there has been a lot of interest in F-Theory GUTs, mostly considering local models. In this talk I first consider an SU(5) GUT locally at the "point of E_8". The requirements of proton stability and reasonable flavour structure single out exactly two models. However, both models cannot be embedded in a semilocal construction (via the spectral cover approach). This casts doubts on the predictivity of local models.

I will discuss the phenomenologically interesting scenario of matter inflation in supersymmetric hybrid inflation models. The inflaton resides in a gauge non-singlet matter multiplet and the eta-problem is solved by a "Heisenberg" symmetry. This symmetry relates the inflaton with a modulus field and we stabilize this modulus via corrections to the Kähler potential. The Heisenberg symmetry arises naturally for the untwisted matter fields in heterotic orbifolds. A way to embed matter inflation into heterotic orbifold compactifications is suggested and moduli stabilization in the extended setup is discussed. I argue that the corrections from moduli stabilization may not spoil the flatness of the inflaton potential at large radius.