Non-Gaussianity Generated by the Entropic Mechanism in Bouncing Cosmologies Made Simple

Abstract

Non-gaussianity in the microwave background radiation is bound to play a key role in giving us clues about the physics of the very early universe. However, the associated calculations, at second and even third order in perturbation theory, tend to be complicated to the point of obscuring simple underlying physical processes. In this note, we present a simple analytic procedure for approximating the non-linearity parameters f_{NL} and g_{NL} for cyclic models in which the cosmological perturbations are generated via the entropic mechanism. Our approach is quick, physically transparent and agrees well with the results of numerical calculations.

Figures (1)

• Figure 1: After the ekpyrotic phase, the trajectory in scalar field space enters the kinetic phase and bends - this bending is described by the existence of an effective repulsive potential (the potentials are indicated by their contour lines). A trajectory adjacent to the background evolution can be characterized by the entropy perturbation $\delta s(t_{ek-end})$ at the end of the ekpyrotic phase, leading to a corresponding off-set $\delta s(t_{bend}),$ or equivalently $\delta V(t_{bend}),$ at the time of bending.