A minimal model of inflation and dark radiation

Kristjan Kannike,Aleksei Kubarski,Luca Marzola,Antonio Racioppi

doi:10.1016/j.physletb.2019.03.025

Kristjan Kannike, Aleksei Kubarski + Show 2 more

Open Access

https://doi.org/10.1016/j.physletb.2019.03.025

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Abstract

We show that a minimal extension of the Standard Model including a new complex scalar field can explain inflation and the observed effective number of neutrinos. The real part of the singlet plays the rôle of the inflaton field, while the Goldstone boson emerging from the spontaneous symmetry breaking of a global U(1) symmetry contributes to dark radiation and increases the effective number of neutrino species by 0.3 over the Standard Model value. After detailing the phenomenology of the model, we find that the predicted inflationary observables are in agreement with the current bounds, once the dark radiation component is allowed, both within the metric and Palatini formulation of non-minimally coupled gravity.

Highlights

According to contemporary understanding, the earliest stage of our Universe presents a period of exponential expansion known as cosmic inflation
We show that a minimal extension of the Standard Model including a new complex scalar field can explain inflation and the observed effective number of neutrinos
The real part of the singlet plays the role of the inflaton field, while the Goldstone boson emerging from the spontaneous symmetry breaking of a global U (1) symmetry contributes to dark radiation and increases the effective number of neutrino species by 0.3 over the Standard Model value

Summary

Introduction

The earliest stage of our Universe presents a period of exponential expansion known as cosmic inflation. Its contribution to the effective number of neutrino species depends on the temperature at which the Goldstone leaves thermal equilibrium with the SM plasma, which is reheated by particle annihilations several times during the evolution of the Universe Fascinated by this possibility, we study a minimal scenario where the dynamics of inflation are entwined with the properties of dark radiation. We introduce a non-minimal coupling between S and the curvature scalar R, which flattens the potential at large field values and generally leads our inflationary solutions towards those of the Starobinsky model [1] In this way we show that the proposed framework can fit the observed effective number of neutrino species.

Goldstone bosons and the effective number of neutrino species

Inflationary Observables

Results