CONSTRAINING INFLATION THROUGH JOINT OBSERVATIONS OF THE PRIMORDIAL GRAVITATIONAL WAVE BACKGROUND

The standard cosmological model leaves many questions unanswered. An early period of accelerated expansion of the Universe, referred to as inflation, resolves these issues. It provides a means to generate perturbations in matter and density that lead to the formation of structure as well as in gravitational waves. Inflation preserves fluctuations by driving them beyond the causal horizon. Their wavelengths trace the time they exit and their amplitude reveals the expansion rate and inflationary potential energy at exit. Measurements of these fluctuations is therefore a powerful probe of the inflationary Universe. After providing the necessary overview of background cosmology and inflation, I explore our ability to constrain viable models using joint measurements at vastly separated length scales and frequencies. Particular attention is paid to observations of the tensor power spectrum at large scales through measurements of the B-mode polarization of the cosmic microwave background and at small scales by direct detection using interferometric gravitational wave detectors. First, I consider a simple test of the inflationary consistency relation and discuss a simple means to constrain the running of the tensor spectral index. Secondly, I investigate more generally how joint observations can restrict viable models and reveal a highly constrained class of likely expansion histories and potential energies driving the expansion. Within these remaining classes of models, subsets are revealed by their spectral tilts at small scales. Thus, the addition of a measure of the tensor spectral tilt at solar system scales amplifies the restrictive power to identify valid inflationary models. I conclude with a discussion of the possible addition of constraints of both the tensor and scalar power spectrum at intermediate scales and some for the challenges that future experiments will need to overcome