One of major advances of string theory in recent years was an understanding that vacuum solutions with potentially viable four-dimensional cosmology come in a plethora of an incredibly large and rich 'landscape' of string theory vacua. The number of possible vacua and, in turn, types of Universes, may exceed 10 to the power 1000.
This progress was enabled by finding ways to give mass to ('stabilize') the moduli. The moduli are the typically 100 to 1000 massless scalar fields which are associated with deformations of extra dimensions required by string theory. Moduli stabilization also gave rise to the first well-controlled string theory constructions of cosmological inflation, a very early burst of exponential expansion of the universe needed to produce its large scale and spatial flatness.
Inflation seeds density perturbations, which are the source of all visible structure in our universe, as well as gravitational wave fluctuations. If the gravitational wave fluctuations are seen (e.g. by the PLANCK satellite), this would tell us that inflation took place at an energy scale only 100 times below Planck scale of quantum gravity and maybe string theory itself. We may then hope for leftover imprints from the fundamental theory in high-scale inflation.
Dr. Westphal will show how string theory has been recently found to push towards deviations from quantum field theory results for high-scale models of inflation which produce detectable gravitational wave fluctuations. He will describe how the next step is understanding the distribution of the energy scale of inflation across the 'landscape' of string theory vacua. This will decide if the peculiarities of high-scale inflation in string theory have any predictive power.