No-Scale Inflation

Abstract

Supersymmetry is the most natural framework for physics above the TeV scale, and the corresponding framework for early-Universe cosmology, including inflation, is supergravity. No-scale supergravity emerges from generic string compactifications and yields a non-negative potential, and is therefore a plausible framework for constructing models of inflation. No-scale inflation yields naturally predictions similar to those of the Starobinsky model based on $R + R^2$ gravity, with a tilted spectrum of scalar perturbations: $n_s∼0.96$, and small values of the tensor-to-scalar perturbation ratio $r < 0.1$, as favored by Planck and other data on the cosmic microwave background (CMB). In this thesis we introduce a novel no-scale inflationary model that averts the stabilization problem of supergravity models; to study it we develop a multi-field formalism applicable to supergravity models. We discuss the low-energy phenomenology of generic no-scale models and its connection to the lifetime of the inflaton. We use our results to analyze the constraints on these models imposed by CMB measurements, which through the calculation of the number of e-folds $N_*$ , we relate to constraints on the inflaton decay rate and other parameters of specific no-scale inflationary models. Finally, we revisit gravitino production following inflation, including thermal and non-thermal effects, and discuss the potential implications of upper limits on the gravitino abundance for no-scale models of inflation. Our results may provide insights into the embedding of inflation within string theory as well as its links to collider physics.