Scale-invariance as the origin of dark radiation?

TL;DR

This paper proposes that scale invariance in high-energy physics can naturally produce dark radiation and explain cosmological observations, linking inflation, reheating, and particle physics scales.

Contribution

It introduces a scale-invariant framework that accounts for dark radiation via dilaton production during reheating, connecting inflationary models with particle physics.

Findings

Dilatons produced at reheating match primordial element abundances.

A lower reheating temperature limit is established for scale-invariant inflation.

The model links inflationary dynamics with dark radiation origins.

Abstract

Recent cosmological data favour R^2-inflation and some amount of non-standard dark radiation in the Universe. We show that a framework of high energy scale invariance can explain these data. The spontaneous breaking of this symmetry provides gravity with the Planck mass and particle physics with the electroweak scale. We found that the corresponding massless Nambu--Goldstone bosons -- dilatons -- are produced at reheating by the inflaton decay right at the amount needed to explain primordial abundances of light chemical elements and anisotropy of the cosmic microwave background. Then we extended the discussion on the interplay with Higgs-inflation and on general class of inflationary models where dilatons are allowed and may form the dark radiation. As a result we put a lower limit on the reheating temperature in a general scale invariant model of inflation.