The Pseudo-Conformal Universe: Scale Invariance from Spontaneous Breaking of Conformal Symmetry

TL;DR

This paper introduces a new early universe model based on conformal symmetry breaking that naturally produces a scale-invariant spectrum of perturbations without requiring inflation, predicting distinctive observational signatures.

Contribution

The authors propose a conformal field theory-based scenario that explains scale invariance through symmetry breaking, offering an alternative to inflation with unique observational predictions.

Findings

Predicts a scale-invariant spectrum of perturbations without inflation

Results in significant non-Gaussianities in the cosmic microwave background

Forecasts the absence of primordial gravitational waves

Abstract

We present a novel theory of the very early universe which addresses the traditional horizon and flatness problems of big bang cosmology and predicts a scale invariant spectrum of perturbations. Unlike inflation, this scenario requires no exponential accelerated expansion of space-time. Instead, the early universe is described by a conformal field theory minimally coupled to gravity. The conformal fields develop a time-dependent expectation value which breaks the flat space so(4,2) conformal symmetry down to so(4,1), the symmetries of de Sitter, giving perturbations a scale invariant spectrum. The solution is an attractor, at least in the case of a single time-dependent field. Meanwhile, the metric background remains approximately flat but slowly contracts, which makes the universe increasingly flat, homogeneous and isotropic, akin to the smoothing mechanism of ekpyrotic cosmology. Our scenario is very general, requiring only a conformal field theory capable of developing the appropriate time-dependent expectation values, and encompasses existing incarnations of this idea, specifically the U(1) model of Rubakov and the Galileon Genesis scenario. Its essential features depend only on the symmetry breaking pattern and not on the details of the underlying lagrangian. It makes generic observational predictions that make it potentially distinguishable from standard inflation, in particular significant non-gaussianities and the absence of primordial gravitational waves.