From Planck data to Planck era: Observational tests of Holographic Cosmology

TL;DR

This paper tests holographic models of the early universe against cosmological data, finding they fit well and are competitive with the standard model, especially at large scales, with some models being observationally viable.

Contribution

It introduces and evaluates holographic cosmological models based on 3D QFT, comparing their fit to data with the standard $b1$CDM model, and constrains the dual QFT theories using observations.

Findings

Holographic models fit large-scale CMB data well.

Standard $b1$CDM has a better overall Bayesian evidence.

Some QFT models are ruled out by observations, others remain viable.

Abstract

We test a class of holographic models for the very early universe against cosmological observations and find that they are competitive to the standard $\Lambda$CDM model of cosmology. These models are based on three dimensional perturbative super-renormalizable Quantum Field Theory (QFT), and while they predict a different power spectrum from the standard power-law used in $\Lambda$CDM, they still provide an excellent fit to data (within their regime of validity). By comparing the Bayesian evidence for the models, we find that $\Lambda$CDM does a better job globally, while the holographic models provide a (marginally) better fit to data without very low multipoles (i.e. $l\lesssim 30$), where the dual QFT becomes non-perturbative. Observations can be used to exclude some QFT models, while we also find models satisfying all phenomenological constraints: the data rules out the dual theory being Yang-Mills theory coupled to fermions only, but allows for Yang-Mills theory coupled to non-minimal scalars with quartic interactions. Lattice simulations of 3d QFT's can provide non-perturbative predictions for large-angle statistics of the cosmic microwave background, and potentially explain its apparent anomalies.