ETD

• climbing phenomenon
• cosmological perturbations
• non-gaussianity
• superstrings
• supersymmetry breaking

Broken supersymmetry in String theory offers promising avenues for non-standard single-field slow-roll. In the climbing phenomenon a scalar, forced to emerge from the initial singularity while climbing up a steep exponential potential up to a turning point, can drive the onset of inflation. The pre–inflationary fast-roll dynamics then cuts the low-k primordial spectrum of curvature perturbations, in a way that resonates with the lack of power in the first few CMB multipoles. This work explores the possible non-Gaussian imprints of this scenario. In Chapter 1 we review the fundamentals of string theory, with emphasis on supersymmetry breaking and the emergence of steep exponential potentials, while in Chapter 2 we illustrate the climbing phenomenon. In chapter 3 we show how a scale Δ can capture the low-k suppression induced by the climbing phenomenon and derive Maldacena’s cubic action. In Chapter 4, we develop an approximate framework for computing the resulting non-Gaussian signatures, within a bouncing Cosmology that resonates with old work of Gasperini and Veneziano. We identify two types of contributions. The first is very small and oscillates around Maldacena’s result with a frequency dictated by the bounce cutoff. However, the second, which originates from the turning point, depends on the number N of inflationary e-folds, and for 63 < N < 65 can lie within current observational bounds on fNL while being potentially detectable.