Primordial Non-Gaussianity from a String-Inspired Cosmology

The interplay between string theory and early-universe cosmology offers promising avenues to explore high-energy regimes where the standard single-field slow-roll model may no longer provide an accurate description. One intriguing scenario emerges from certain non-supersymmetric string models, where supersymmetry breaking induces a non-trivial vacuum energy, or more precisely an exponential potential for scalar fields, and primarily for the dilaton. This setup gives rise to the so-called "climbing scalar" phenomenon, whereby the scalar is forced to emerge from the initial singularity while climbing up the potential, if sufficiently steep. This phase precedes a turning point, and the subsequent descent can support inflation. The resulting pre-inflationary dynamics can leave imprints in cosmological observables. To begin with, it induces a low-frequency cut in the primordial power spectrum that resonates with the lack of power present in the first few CMB multipoles. The main theme of this work is to clarify its possible effect on non-Gaussianities.