Axion dark matter with high-scale inflation

Eung Jin Chun

doi:10.1016/j.physletb.2014.06.017

Abstract

We show that supersymmetric axion models breaking the PQ symmetry by the interplay of non-renormalizable supersymmetric terms and soft supersymmetry breaking terms provide a natural framework not only for generating the axion scale from soft supersymmetry breaking scale m3/2 but also for enhancing it during inflation by factor of order HI/m3/2 where HI≃1014 GeV according to the recent BICEP2 result. In this scheme, the PQ symmetry can stay broken throughout the whole history of the Universe if the reheat temperature is below 1010 GeV, or m3/2 when the PQ fields couple strongly to thermal (Standard Model) particles. It is also shown that parametric resonance during preheating is not effective enough to induce non-thermal PQ symmetry restoration. As a consequence, axion models with the QCD anomaly NDW>1 can be made free from the domain wall problem while the axion isocurvature perturbation is suppressed sufficiently for the axion scale during inflation larger than about MP(Ωah2/0.12)1/2(Fa/1012 GeV)0.6 GeV.

Highlights

The recent measurement of CMB B-mode polarizations by BICEP2 points to large primordial tensor perturbations with the tensor-to-scalar ratio r = O(0.1) [1]
We present a natural framework where the PQ symmetry is never restored throughout the whole history of the Universe, and the PQ symmetry breaking scale during inflation is much larger than the present one so that the domain wall problem occurring in axion models with the QCD anomaly NDW > 1 can be avoided, and the axion isocurvature density perturbation can be sufficiently suppressed
If the PQ symmetry is broken after inflation, there appear three sources of axion production: coherent oscillation from initial misalignment by θi, axionic string formation upon the PQ symmetry breaking, and domain wall production during the QCD phase transition

Summary

Introduction

The recent measurement of CMB B-mode polarizations by BICEP2 points to large primordial tensor perturbations with the tensor-to-scalar ratio r = O(0.1) [1]. This reveals a high-scale inflation with the Hubble parameter, HI. We present a natural framework where the PQ symmetry is never restored throughout the whole history of the Universe, and the PQ symmetry breaking scale during inflation is much larger than the present one so that the domain wall problem occurring in axion models with the QCD anomaly NDW > 1 can be avoided, and the axion isocurvature density perturbation can be sufficiently suppressed. Being a pseudo-Goldstone boson of a QCD-anomalous U (1) symmetry (PQ symmetry) the axion couples to the CP-odd QCD field strength term; LQCD

Fa is the axion decay constant and

VS U S Y

Conclusion