Gravitational Fluctuations as an Alternative to Inflation III. Numerical Results

TL;DR

This paper refines a quantum gravity-based model for cosmological power spectra using advanced numerical tools, aiming to distinguish it from inflationary models despite current observational limitations.

Contribution

It introduces an updated numerical analysis of a quantum gravity model for cosmological spectra, removing previous approximations and providing detailed predictions for observational tests.

Findings

Predictions for matter power spectrum P(k)

Predictions for CMB angular spectra (TT, TE, EE, BB)

Potential to distinguish quantum gravity vacuum condensate from inflation models

Abstract

Power spectra play an important role in the theory of inflation, and their ability to reproduce current observational data to high accuracy is often considered a triumph of inflation, largely because of a lack of credible alternatives. In previous work we introduced an alternative picture for the cosmological power spectra based on the nonperturbative features of the quantum version of Einstein's gravity, instead of currently popular inflation models based on scalar fields. The key ingredients in this new picture are the appearance of a nontrivial gravitational vacuum condensate (directly related to the observed cosmological constant), and a calculable renormalization group running of Newton's G on cosmological scales. Results obtained previously were largely based on a semi-analytical treatment, and often suffered from the limitations of various approximations and simplifying assumptions. In this work, we extend and refine our previous calculations by laying out an updated and extended analysis, which now utilizes a set of suitably modified state-of-the-art numerical programs (ISiTGR, MGCAMB and MGCLASS) developed for observational cosmology. As a result, we are able to remove some of the approximations employed in our previous studies, leading to a number of novel and detailed physical predictions. These should help in potentially distinguish the vacuum condensate picture of quantum gravity from that of other models such as scalar field inflation. Here, besides the matter power spectrum P(k), we work out in detail predictions for what are referred to as the TT, TE, EE, BB angular spectra, as well as their closely related lensing spectra. However, the current limited precision of observational data today (especially on large angular scales) does not allow us yet to clearly prove or disprove either set of ideas.