Thermal non-Gaussianity in holographic cosmology

TL;DR

This paper investigates the non-Gaussian features of thermal holographic fluctuations in cosmology, revealing that certain matter conditions can produce significant non-Gaussianity, with potential observational implications.

Contribution

It calculates the non-Gaussianity of holographic cosmological fluctuations and explores how matter properties influence its magnitude and sign.

Findings

Non-Gaussianity can reach or exceed order 1 for phantom-like matter.

In the limit ω→ -5/3, non-Gaussianity becomes very large and negative.

Non-Gaussianity depends linearly on wavenumber k when temperature variation is neglected.

Abstract

Recently it has been shown that the thermal holographic fluctuations can give rise to an almost scale invariant spectrum of metric perturbations since in this scenario the energy is proportional to the area of the boundary rather than the volume. Here we calculate the non-Gaussianity of the spectrum of cosmological fluctuations in holographic phase, which can imprint on the radiation dominated universe by an abrupt transition. We find that if the matter is phantom-like, the non-Gaussianity $f_{NL}^{equil}$ can reach ${\cal O}(1)$ or even be larger than ${\cal O}(1)$. Especially in the limit $\omega\to -5/3$, the non-Gaussianity is very large and negative. Furthermore, since the energy is proportional to the area, the thermal holographic non-Gaussianity depends linearly on $k$ if we neglect the variation in $T$ during the transition (fixed temperature).