Natural inflation with hidden scale invariance

Neil D Barrie,Shelley Liang,Archil Kobakhidze

doi:10.1016/j.physletb.2016.03.056

Neil D Barrie, Shelley Liang + Show 1 more

Open Access

https://doi.org/10.1016/j.physletb.2016.03.056

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Abstract

We propose a new class of natural inflation models based on a hidden scale invariance. In a very generic Wilsonian effective field theory with an arbitrary number of scalar fields, which exhibits scale invariance via the dilaton, the potential necessarily contains a flat direction in the classical limit. This flat direction is lifted by small quantum corrections and inflation is realised without need for an unnatural fine-tuning. In the conformal limit, the effective potential becomes linear in the inflaton field, yielding to specific predictions for the spectral index and the tensor-to-scalar ratio, being respectively: $n_s-1\approx -0.025\left(\frac{N_{\star}}{60}\right)^{-1}$ and $r\approx 0.0667\left(\frac{N_{\star}}{60}\right)^{-1}$, where $N_{\star}\approx 30-65$ is a number of efolds during observable inflation. This predictions are in reasonable agreement with cosmological measurements. Further improvement of the accuracy of these measurements may turn out to be critical in falsifying our scenario.

Highlights

Cosmic inflation is an attractive paradigm for the very early universe that resolves some outstanding puzzles of the standard hot Big Bang cosmology, such as the horizon and flatness problems [1, 2, 3]
It provides a natural mechanism for generation of nearly scaleinvariant inhomogeneities through the quatum fluctuations of the inflaton field, that at later stages result in the observed large scale structure of the universe [7]
Our key observation is that in a very generic scale-invariant model, with an arbitrary number of scalar fields and non-renormalizable operators in the scalar potential, there always exists a direction in field space which is absolutely flat in the classical limit

Summary

Introduction

Cosmic inflation is an attractive paradigm for the very early universe that resolves some outstanding puzzles of the standard hot Big Bang cosmology, such as the horizon and flatness problems [1, 2, 3] (for important precursor works see [4, 5, 6]). The basic theory of inflation involves a scalar field, the inflaton (φ), which slowly rolls down the potential hill. In this paper we would like to propose a new class of natural inflation models based on a hidden scale invariance, realised through the pseudo-Goldstone boson of a spontaneously broken anomalous scaling symmetry, the dilaton.

Results

Conclusion