String Cosmology: The Pre-Big Bang Scenario
G. Veneziano
TL;DR
The paper surveys the pre-big bang scenario in string cosmology, arguing that string-theory features such as a minimal length and duality-induced inflation can yield a long, asymptotically trivial past that evolves into a high-curvature, non-perturbative phase. It analyzes the theoretical foundations (frames, symmetries, and initial data) and the phenomenological predictions, including spectra of tensor, dilaton, axion, and gauge-field perturbations, as well as heating and entropy considerations. A central challenge is the graceful exit from the pre-big bang phase to standard FRW cosmology, with multiple proposed mechanisms—ranging from higher-derivative corrections to quantum tunnelling and non-local potentials—though a definitive solution remains elusive. The work emphasizes the potential of PBB to test string cosmology through observable relics while acknowledging the need for data-driven validation and further theoretical development, particularly regarding exit dynamics and perturbation evolution.
Abstract
A review is attempted of physical motivations, theoretical and phenomenological aspects, as well as outstanding problems, of the pre-big bang scenario in string cosmology.