Fingerprints of a Non-Inflationary Universe from Massive Fields

TL;DR

This paper demonstrates that massive fields in a slowly contracting ekpyrotic universe produce unique oscillatory signals in the primordial power spectrum, serving as model-independent fingerprints to distinguish early universe scenarios from inflation.

Contribution

The study constructs explicit classical primordial standard clock models in a non-inflationary ekpyrotic universe and analyzes their distinctive observational signatures.

Findings

Oscillatory features differ from inflation predictions

Clock signals can discriminate early universe models

Numerical results confirm analytical estimates

Abstract

We construct explicit models of classical primordial standard clocks in an alternative to inflation, namely the slowly contracting ekpyrotic scenario. We study the phenomenology of massive spectator fields added to a state-of-the-art ekpyrotic model, with coupling functions that allow for these heavy fields to be classically excited while the background is slowly contracting. We perform numerical computations of the corrections to the scalar primordial power spectrum and compare with analytical estimates. Our full numerical results reveal so-called clock signals, sharp feature signals, as well as signals that link the two together. The models are found to predict oscillatory features that are resolutely different from what is calculated in inflation, and thus, such features represent unique fingerprints of a slowly contracting universe. This confirms the capability of primordial standard clocks to model-independently discriminate among very early universe scenarios.